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Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing carbazole unit

Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing... Int J Ind Chem (2017) 8:329–343 DOI 10.1007/s40090-017-0112-5 RESEARCH Synthesis, characterization and electrochemical properties of poly (phenoxy-imine)s containing carbazole unit 1 1 1,2 İsmet Kaya Sebra Çöpür Hatice Karaer · · Received: 29 June 2016 / Accepted: 11 January 2017 / Published online: 27 January 2017 © The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Several new Schiff base polymers were synthe- Keywords Carbazole · Fluorescence · Thermal analysis · sized via oxidative polymerization method in an aqueous Poly(phenoxy-imine) · Band gaps alkaline medium in the presence of NaOCl as an oxidant 1 13 and were confirmed by FT-IR, H-NMR, C-NMR and UV–Vis spectroscopic techniques. Furthermore, cyclic Introduction voltammetry measurements were carried out and the HOMO–LUMO energy levels and electrochemical band Poly(imine)s, known as Schiff base polymers or poly gaps (E ′) were calculated. Additionally, the optical band (azomethine)s or also named polyazines (when hydrazine gaps (E ) were determined using their UV–Vis spectra of is used as diamine compound) [1] which are of great the materials. The morphologic properties of the polymers interest to researchers because of to their potential appli- were investigated by scanning electron microscopy. In cations and advantageous properties. Recently, addition, the number average molecular weight (M ), polyazomethines have attracted much attention of both weight average molecular weight (M ) and polydispersity industries and academia and they have been widely index values of the polymers were determined by gel investigated for their electrochemical properties, thermal permeation chromatography technique. Electrical conduc- stability, fluorescence, intrinsic conductivity [2]. tivity measurements of the doped (with iodine) and Polyimines conjugated polymers have claimed the undoped polymer related to doping time were carried out attention of researchers because of their potentially advan- by four-point probe technique using a Keithley 2400 tageous electronic applications, such as their electrical electrometer. Their thermal behaviors were determined by properties and environmentally stability, with accept- TG–DTA and DSC measurements. The synthesized com- able mechanical strength [3]. Polyazomethines are pounds were soluble in common solvents such as DMF, conducting polymers [4] that usually show an optical THF and DMSO. Photoluminescence properties of the absorption band in the visible region owing to their extended polymers were determined in different concentrations of delocalization of the π electrons along the polymer back- DMF solvent. bone. Upon doping with suitable dopants, charge carriers, namely bipolaron and polaron, are formed in the conjugated backbone. This class of polymers was primarily found to be electroactive as well as semiconductive materials [5, 6], and their conductivity could be increased by doping with a & Ismet Kaya dopant like iodine [2]. Furthermore, Schiff base polymers kayaismet@hotmail.com have been become increasingly interesting in the field of optical materials since they possess great potential for device Polymer Synthesis and Analysis Laboratory, Department applications like light-emitting diodes, photovoltaic cells of Chemistry, C¸ anakkale Onsekiz Mart University, 17020 C¸ anakkale, Turkey and thin film transistors [7]. Poly(azomethine)s including conjugated bonding and Department of Chemistry, Faculty of Sciences, active hydroxyl group have been studied for more than Dicle University, 21280 Diyarbakır, Turkey 123 330 Int J Ind Chem (2017) 8:329–343 60 years, and used in several fields [8]. The oxidative and C-NMR measurements. Thermal stabilities of all polymerization method is simply the reaction of com- compounds were determined by TG–DTA and DSC mea- pounds including –OH groups and active functional groups surements. Also, the conductivity and photoluminescence (–CHO, –NH , –COOH) in their structure with the oxidants (PL) properties of polymers were determined from four- like air oxygen NaOCl, H O an in the aqueous alkaline point probe technique and spectrofluorophotometer mea- 2 2 medium [9]. surements, respectively. Carbazole-containing polymers are of great interest owing to their several potential for applications in organic electronics, such as organic solar cells, organic field effect Experimental transistors (OFET) and organic light-emitting devices (OLED), etc. [10]. Materials In this study, new Schiff bases were synthesized by condensation reaction of 4-diethylaminosalicylaldehyde, 3-Amino-9-ethyl-carbazole, ethyl alcohol, ethyl acetate, 3,4-dihydroxybenzaldehyde and 2,4-dihydroxybenzalde- chloroform, N,N-dimethylacetamide, N,N-dimethylfor- hyde compounds with 3-amino-9-ethyl-carbazole. Then, mamide, dimethyl sulfoxide, acetonitrile and sodium these products were polymerized via oxidative polycon- hypochlorite (NaOCl, 37%) were supplied from Merck densation method in an aqueous alkaline medium in the Chemical Co. (Germany). 4-Diethylamino salicylaldehyde presence of NaOCl as an oxidant. The structures of all (Alfa Aesar), 3,4-dihydroxybenzaldehyde (Fluka) and 2,4- compounds were confirmed by FT-IR, UV–Vis, H-NMR dihydroxybenzaldehyde were supplied from Acros. Scheme 1 Syntheses of Schiff bases and their polymers 123 Int J Ind Chem (2017) 8:329–343 331 Synthesis of the monomers (DEACIMP, ACIMB Characterization techniques and ACIBM) A PerkinElmer spectrum one FT-IR system was used to The synthesis of 5-(diethylamino)-2-[(3-amino-9-ethyl- determine the chemical structure of the monomers and poly- carbazole) imino methyl] phenol (DEACIMP) was syn- mers. Measurements were performed in solid powder form at thesized according to the literature [11] (Scheme 1)as room temperature using universal ATR sampling accessory −1 follows: 4-diethylamino salicylaldehyde (1.77 g) and within the wavelengths of 4000–650 cm .UV–Visspec- 3-amino-9-ethyl-carbazole (1.95 g) were dissolved in troscopy, was used to study the electronic transition in the 20 mL absolute ethanol in two separate beakers, which were then mixed. This mixture was refluxed for 5 h in a two-necked flask and cooled to room temperature. The precipitate formed was filtered, washed with ethanol and then dried under reduced pressure. The same procedure was used to obtain 4-[(3-amino-9-ethyl-carbazole) imino methyl] benzene-1,2-diol (ACIMB) and 4-[(3-amino-9- ethyl-carbazolyl) benzene imine methyl]-1,3-diol (ACIBM) the 3,4-dihydroxybenzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) and 2,4-dihydroxy- benzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) were used for synthesis the ACIMB and ACIBM, respec- tively. The yields of DEACIMP, ACIMB and ACIBM compounds were found to be 80, 85, 89, respectively. General synthesis procedure of P-DEACIMP, P-ACIMB and P-ACIBM polymers P-DEACIMP, P-ACIMB and P-ACIBM were synthe- sized through the oxidative polycondensation of DEACIMP, ACIMB and ACIBM with aqueous solution of NaOCl (10%). P-DEACIMP was synthesized through oxidative polycondensation of 5-(diethylamino)-2-[(3- amino-9-ethyl-carbazole) imino methyl] phenol using aqueous solution of NaOCl (10%). The 5-(diethy- lamino)-2-[(3-amino-9-ethyl-carbazole) imino methyl] phenol (0.385 g) was dissolved in an aqueous solution of 25 mL KOH (1.0 M) placed into a 100-mL three-necked round-bottom flask, which was fitted with a condenser, thermometer. Furthermore, a funnel containing NaOCl, which was added dropwise over about 30 min, was equipped. The reaction mixture was stirred at 100 °Cfor 24 h, cooled to room temperature and then 25 mL HCl (1.0 M) was added to solution. The P-DEACIMP was washed with water for the separation from mineral salt. The polymers were dried at 60 °Cinanovenfor 24 h [8, 12, 13]. The same procedure was used to obtain the P-ACIMB and P-ACIBM but the 4-[(3-amino-9-ethyl-carbazole) iminemethylbenzene]-1,2-diol (ACIMB) (0.33 g) and 4-[(3-amino-9-ethyl-carbazole) iminomethylbenzene]-1,3- diol (ACIBM) (0.33 g) were used for synthesis the P-ACIMB and P-ACIBM, respectively (Scheme 1). The yields of P-DEACIMP, P-ACIMB and P-ACIBM com- Fig. 1 FT-IR spectra of the monomers and polymers pounds were found to be 70, 72, 76, respectively. 123 332 Int J Ind Chem (2017) 8:329–343 Table 1 FT-IR spectral data of −1 Compounds Wave number (cm ) monomers and polymers –OH C–H (aromatic) C–H (aliphatic) –C=N C=C (aromatic) C–O DEACIMP 3300 2973 2936 1600 1587, 1522 – P-DEACIMP – 2978 2927 1604 1532, 1486 1227 ACIMB 3665 2976 2905 1615 1495, 1473 – P-ACIMB – 2979 2895 1602 1489, 1460 1223 ACIBM 3393 2983 2911 1608 1492, 1476 – P-ACIBM – 2976 2908 1608 1544, 1463 1217 UV–Vis region of the all compounds. Measurements were of the monomers and polymers are shown in Fig. 1. performed by an AnalytikJena Specord 210 Plus with wave- According to these spectra, the characteristic peaks such as length range of 190–900 nm by ethyl alcohol solvent at 25 °C. etheric groups, aromatic and aliphatic C–H stretching 1 13 Hand C NMR spectra (Bruker AV400 FT-NMR spec- peaks are observed, as expected. The peaks related to Ar–O −1 trometer operating at 400.1 and 100.6 MHz, respectively) bonds are in the range of 1217–1235 cm [14], indicating were also recorded in DMSO-d at 25 °C. The tetramethyl- that the polymerization was achieved. The bands due to silane was used as internal standard. Thermal data were hydroxyl groups (–OH) are observed at around 3300– −1 obtained by using a PerkinElmer diamond thermal analysis 3670 cm (Fig. 1)[15]. system. TGA–DTA measurements were performed between Aromatic –CH peaks were observed at around −1 −1 20 and 1000 °C(in N ,rate 10 °Cmin ). DSC analyses of 2980 cm for all the compounds. Furthermore, peaks at −1 polymers were carried out by a PerkinElmer Pyris sapphire 1450–1650 cm were assigned to benzene ring and (C=C) −1 DSC. DSC measurements were conducted between 25 and moiety and those at 1522–1590 cm were attributed to (C– −1 450 °C(in N ,rate 10 °Cmin ). The number average O) stretching [16] while peaks for aliphatic group were −1 molecular weight (M ), weight average molecular weight seen at 2900–2940 cm . −1 (M ) and polydispersity index (PDI) were determined by gel The peak at 1600–1620 cm corresponds to –CH=N permeation chromatography-light scattering (GPC-LS) stretching vibration of imine moiety. The peaks of vibra- device by Malvern Viscotek GPC Dual 270 max. For GPC tion bonding are also shown in Table 1. As seen in Fig. 1, investigations a medium 300 9 8.00 mm dual column light peaks of polymers were broader than that of monomers scattering detector (LS) and a refractive index detector (RID) after the polycondensation reaction owing to their poly- were used to analyze the products at 55 °C. LiBr (40 mM) was conjugated structures. Other characteristic absorption added to the DMF mobile phase to dissociate molecular bands are also presented in Table 1. aggregates of polymer during GPC analysis. Surface mor- Furthermore, the edged peaks of P-DEACIMP, phology of the polymers was determined by scanning electron P-ACIMB and P-ACIBM were broader and decreased microscope (SEM) (JEOL, JSM-7100 model). Cyclic numerically due to the increase in molecular weight after voltammetry (CV) measurements were carried out with a CH polymerization reactions [17], confirming polymerization 660 C Electrochemical Analyzer (CH Instruments, Texas, of DEACIMP, ACIMB and ACIBM. 1 13 USA) at a potential scan rate of 20 mV/s. A Shimadzu RF- H NMR and C NMR spectra of the monomers and 5301PC spectrofluorophotometer was used in fluorescence polymers were recorded in DMSO-d . Hdataof the measurements. Emission spectra of the synthesized polymers monomers and polymers are listed in Table 2 and the were obtained in different concentration of DMF solvent. spectrum of a representative polymer P-DEACIMP and 1 13 Also, to obtain maximal emission intensity values of polymers DEACIMP are shown in Fig. 2.The Hand CNMR were investigated in different concentrations of DMF spectra of DEACIMP and P-DEACIMP data are given in 1 13 solutions. Figs. 2 and 3. Hand C NMR data results of the synthe- sized compounds are listed in Table 2 except for DEACIMP and P-DEACIMP. When phenol-based Schiff bases were Results and discussion polymerized by oxidative polycondensation, they were combined by C–C binding at ortho and/or para position of Structural characterization of the monomers the ring or alternatively C–O–C binding through oxygen and polymers atom of –OH moiety (Scheme 1)[2, 18]. H-NMR spectra of the polymers contained three types of signals assigned as The structures of the monomers and polymers were con- follows: the singlet at 8.05–8.98 ppm, –CH=N–; the multiple 1 13 firmed by FT-IR, H and C-NMR spectra. FT-IR spectra at 6.40–8.50 ppm, aromatic protons. The proton resonances 123 Int J Ind Chem (2017) 8:329–343 333 Table 2 NMR spectra data of the monomers and polymers Compounds NMR spectra data H NMR (DMSO-d , ppm, δ): 10.25 and 14.08 (s, –OH), 1.30 (t, Ar–He), 4.43 (m, Ar–Hd), 6.48–8.20 (m, Ar–H), 8.25 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 118 (C1-H), 121 (C2-H and C3-H), 126 (C4-ipso), 133 (C5-ipso), 109 (C6-H), 107 (C7-ipso), 138 (C8-ipso), 38 (C9-H), 14 (C10- H), 112 (C11-H), 160 (C12-ipso), 162 (C13-H), 139 (C14-ipso), 156 (C15-H), 140 (C16-H), 161 (C17-ipso), 129 (C18-H), 115 (C19-H), 122 (C20-H and C21- H) H NMR (DMSO-d , ppm, δ): 11.02 and 13.20 (s, –OH), 1.27 (t, Ar–He), 4.38 (q, Ar–Hd), 7.40–8.03 (m, Ar–H), 8.05 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 133 (C1-H), 110 (C2-H), 121 (C3-H), 118 (C4-H), 120 (C5-H), 126 (C6-ipso), 105 (C7-ipso), 135 (C8-ipso), 36 (C9-H), 14 (C10- H), 111 (C11-H), 160 (C12-ipso), 165 (C13-H), 118 (C14-ipso), 107 (C15-H), 126 (C16-ipso), 161 (C17-ipso), 123 (C18-ipso), 139 (C19-ipso), 125 (C20-H), 112 (C23-H) H NMR (DMSO-d , ppm, δ): 10.24 and 14.07 (s, –OH), 1.31 (t, Ar–He), 4.45 (m, Ar–Hd), 6.48–8.20 (m, Ar–H), 8.96 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 121 (C1-H), 119 (C2-H), 122 (C3-H and C4-H), 126 (C5-ipso), 109 (C6-H), 102 (C7-ipso), 133 (C8-ipso), 39 (C9-H), 15 (C10- H), 112 (C11-H), 140 (C12-ipso), 160 (C13-H), 118 (C14-ipso), 162 (C15-ipso and C18-ipso), 107 (C16-H), 118 (C17-H), 109 (C19-H), 121 (C20-H) H NMR (DMSO-d , ppm,) δ): 11.00 and 13.00 (s, –OH), 7.22–8.33 (m, Aromatic protons), 8.87 (s, –CH=N), 1.30 (t, Ar–He), 4.43 (m, Ar–Hd). C NMR (DMSO-d , ppm, δ): 126 (C1-ipso), 107 (C2-H), 120 (C3-H), 116 (C4-H), 120 (C5-H), 125 (C6-ipso), 103 (C7-ipso), 127 (C8-ipso), 40 (C9-H), 14 (C10-ipso), 112 (C11-H), 140 (C12-ipso), 160 (C13-H), 110 (C14-ipso), 129 (C15-H), 116 (C16-ipso), 164 (C17-ipso), 126 (C18-ipso), 156 (C19-ipso), 112 (C20-H), 125 (C21-H) of hydroxyl (–OH) groups were observed at 12.01, 10.25 The azomethine protons are observed in 8.84, 8.25 and and 14.08, 10.24 and 14.07 ppm for DEACIMP, ACIMB 8.96 ppm for DEACIMP, ACIMB and ACIBM monomers, and ACIBM, respectively. The proton signal of hydroxyl (– 8.90, 8.05 and 8.87 ppm for P-DEACIMP, P-ACIMB and OH) groups were observed at 12.85, 11.02 and 13.20, 11.00 P-ACIBM polymers, respectively. The H NMR spectra of and 13.00 ppm for P-DEACIMP, P-ACIMB and P-ACIBM, polymers shows broad signals for aromatic protons which respectively. Meanwhile, the FT-IR spectra of polymers confirm the participation of aromatic ring in polymeriza- −1 show bands in 1217, 1223 and 1227 cm is assignable to tion [2, 19]. New signals were observed in the region of the phenolic C–O stretching vibration [2]. 169, 162 and 168 ppm in the C NMR spectra of 123 334 Int J Ind Chem (2017) 8:329–343 Fig. 2 H NMR spectra of DEACIMP and P-DEACIMP P-DEACIMP, P-ACIMB and P-ACIBM, respectively, due according to a polystyrene standard calibration curve. The to –C–O–C– coupling, confirming polymerization occurred weight average molecular weight (M ) and polydispersity via –OH moiety [20]. index (PDI, M /M ) values of P-DEACIMP, P-ACIBM and w n Appearance of the new short resonances at 109,148 and P-ACIMB were found to be 8350, 6400, and 9200 and 1.25, 135,139 ppm obviously indicate polymerization of DEA- 1.22 and 1.27, respectively. These results also agree with the CIMP, ACIMB and ACIBM, respectively, i.e., –C–C solubility tests. P-ACIBM had lower molecular weight than binding occurs at ortho or para position of phenol by distri- P-DEACIMP and P-ACIMB polymers. So it was a fine-soluble bution of the phenoxy radical to the ring. The azomethine and polymer in common organic solvents and the others had lower aromatic carbon signals were observed at 159 and 97–163, solubilities owing to their high-molecular weighted structures. 162 and 107–161, 160 and 102–162 ppm in the CNMR spectra of DEACIMP, ACIMB and ACIBM, respectively. Optical properties of compounds Thus, we can easily conclude that the NMR data confirming the structures of the aimed products. UV–Vis spectra of the compounds recorded in ethyl alco- hol at room temperature are given in Fig. 4. Their optical GPC analysis of polymers band gaps (E ) were calculated as in the literature [21] and results are shown in Table 3. Gel permeation chromatography (GPC) analyses of com- E ¼ 1242=k ; ð1Þ g onset pounds (P-DEACIMP, P-ACIBM and P-ACIMB) were where λ is the onset wavelength which may be deter- performed at 55 °C by DMF as eluent at a flow rate of onset −1 mined by intersection of two tangents on the absorption 1.0 mL min . The number average molecular weight (M ), edges. λ also indicates the electronic transition start weight average molecular weight (M ) and polydispersity onset wavelength. According to results, one can easily conclude index (PDI, M /M ) values of compounds were calculated w n 123 Int J Ind Chem (2017) 8:329–343 335 Fig. 3 C NMR spectra of DEACIMP and P-DEACIMP −1 Fig. 4 Absorption spectra of the monomers and polymers (conc.: 100 mg L in ethyl alcohol solvent) that the polymers have low optical band gaps. Because of It is known that the solubility behavior is very advan- monomers and polymers compounds to be having the same tageous for the processing of these materials for functional groups, some UV–Vis absorption bands of their technological applications [4]. Thus, the solubility prop- were observed as similar. erties of the polymers and monomers were tested in 123 336 Int J Ind Chem (2017) 8:329–343 Table 3 Optical electronic a b c d e f Compound E (eV) λ (nm) E (eV) E (eV) HOMO (eV) LUMO (eV) E ′ (eV) g onset ox red g structure parameters of the monomers and polymers DEACIMP 2.43 510 1.44 −1.73 −5.83 −2.66 3.17 P-DEACIMP 2.41 515 1.28 −1.30 −5.67 −3.09 2.58 ACIMB 2.60 478 1.32 −1.29 −5.71 −3.10 2.60 P-ACIMB 3.13 396 1.29 −1.23 −5.68 −3.16 2.51 ACIBM 3.05 406 0.92 −1.33 −5.31 −3.06 2.25 P-ACIBM 3.01 412 0.80 −0.74 −5.19 −3.65 1.54 Optical band gap Oxidation peak potential Reduced peak potential Highest occupied molecular orbital Lowest unoccupied molecular orbital Electrochemical band gap Table 4 Solubility Solvent DEACIMP ACIMB ACIBM P-DEACIMP P-ACIMB P-ACIBM characteristics of the monomers −1 and polymers (1 mg mL )at DMF ++ + + + + 25 °C DMA ++ + + + + DMSO ++ + + + + THF ++ + + + + Ethyl acetate ++ + ⊥ −− Chloroform ++ + ⊥⊥ ⊥ Acetone ++ + ⊥⊥ ⊥ Ethanol ++ + ⊥⊥ ⊥ Acetonitrile ++ + ⊥⊥ + (+), soluble; (⊥), partially soluble; (−), insoluble different solvents by using 1 mg of compound in 1 mL significant conformational differences between ground solvent and shown in Table 4. state (S ) and the first excited state (S ). If the Δλ value is 0 1 ST Fluorescence properties of the synthesized compounds too small, the emission and excitation spectra will overlap are determined using DMF solutions at different concen- more. So the emitted light will be self-absorbed and the trations [22]. Also, the optimization of the concentrations photoluminescence efficiency will decrease. Δλ values ST to obtain maximal emission intensity is investigated in are listed in Table 5. Δλ values of P-DEACIMP, ST DMF. Concentration effects on the fluorescence properties P-ACIMB and P-ACIBM are calculated as 48, 31 and 61, are shown in Fig. 5. Maximum emission intensity values of respectively. According to Δλ values, the synthesized ST the compounds are also given in Table 5. When concen- P-ACIBM can be used for the production of fluorescence tration of DEACIMP, P-DEACIMP, ACIMB were sensor owing to high Δλ value [23]. It can be seen from ST decreased, they showed bathochromic shift in the range Fig. 5 that with increase in the concentrations of the 14–35 nm. On the other hand, a significant change in the solutions, the absorption spectra of the compounds were emission wavelength of these polymers was not observed. observed to shift to the visible region. As seen in Table 5, these results showed that P-ACIMB polymer has higher emission intensity values at Thermal properties of the polymers −6 −5 −1 9.76 9 10 and 1.95 9 10 gmL than the other syn- thesized polymers and monomers. But P-DEACIMP and Thermal degradation data (TGA–DTA and DTG) are listed ACIBM have the lowest emission intensity as polymer and in Table 6. TGA curves of the synthesized monomers and monomer, respectively. polymers are also shown in Fig. 6. According to the TGA Stokes shift (Δλ ) is the difference between positions of results, the initial degradation temperatures (T ) of the ST on the band maxima of emission and excitation spectra of the monomers are higher than their polymers, expect for same electronic transition. This knowledge offers P-ACIBM. This could be explained by the formation of C– 123 Int J Ind Chem (2017) 8:329–343 337 Fig. 5 Emission spectra of the synthesized monomers and polymers in different concentrations (PL intensity photoluminescence intensity, slit width: 3 nm, in DMF solvent) O etheric bond during polymerization. This weak bond is were 23, 16; 21 and 35% at these steps, respectively. easily broken at mild temperatures and makes the polymer P-DEACIMP, P-ACIMB and P-ACIBM polymers were thermally unstable [21, 22]. Furthermore, when % char degraded in two steps: between 230–370, 209–380 and amounts are compared, % char of ACIMB was higher than 201–620 for the first step; 370–570, 380–600 and 620– other compounds at 1000 °C. In addition, Table 6 exhibits 1000 °C for the second step and their weight losses were listed temperatures corresponding to 5, 10, 20 and 50% 53, 37, 50; 25, 22 and 14% at these steps, respectively. weight losses of the all compounds. T values of mono- According to DSC measurements of polymers, the T on g mers and polymers were found between 219–320 and 201– and C values of P-DEACIMP, P-ACIMB, and P-ACIBM 230 °C, respectively. According to TG curves of ACIMB, were found to be 123, 105 and 104 °C and 2.083, 0.086, −1 −1 ACIBM, P-DEACIMP, P-ACIMB, and P-ACIBM, the and 0.075 J g K , respectively. The results indicated that losses of absorbed water were found to be 2, 1.7, 2.7, 5.1 P-DEACIMP has the highest T . and 3.9%, respectively, between 20 and 150 °C. DEACIMP monomer was degraded at the one step between 320 and Morphologic properties 540 °C and its weight loss was 86.5% at this step. ACIMB and ACIBM monomers were degraded in two steps: Morphological properties of the polymers are obtained by between 220–385 and 219–308 for the first step; 385–690 SEM technique. SEM images of compounds were recorded and 308–665 °C for the second step and their weight losses using a Jeol JSM-7100F Schottky instrument in a powder 123 338 Int J Ind Chem (2017) 8:329–343 Table 5 The maximum emission intensity values that obtained from fluorescence spectra of the monomers and polymers as a function of concentration −1 a b c d e f g Compounds Concentration (mg mL ) ƛ (nm) ƛ (nm) ƛ (nm) ƛ (nm) Ι Ι Δƛ ex em max(ex) max(em) ex em ST −5 DEACIMP 6.250 9 10 460 496 450 495 305 260 35 −5 3.125 9 10 460 496 467 495 378 332 35 −5 1.563 9 10 460 496 473 495 412 140 35 −3 P-DEACIMP 1.250 9 10 513 555 498 561 272 200 48 −4 6.250 9 10 513 555 512 561 264 258 48 −4 3.125 9 10 513 555 532 561 247 34 48 −4 ACIMB 6.250 9 10 475 514 460 515 243 117 60 −4 3.125 9 10 475 514 474 515 237 241 60 −4 1.563 9 10 475 514 484 515 233 204 60 −5 P-ACIMB 3.90 9 10 416 478 385 447 574 302 31 −5 1.95 9 10 416 478 380 447 [1000 338 31 −6 9.75 9 10 416 478 375 447 [1000 317 31 −3 ACIBM 2.250 9 10 528 568 526 561 233 204 33 −3 1.125 9 10 528 568 519 561 237 117 33 −4 5.625 9 10 528 568 518 561 243 241 33 −4 P-ACIBM 7.80 9 10 384 449 381 445 224 589 61 −4 3.90 9 10 384 449 380 445 602 586 61 −4 1.95 9 10 384 449 379 445 572 558 61 Excitation wavelength for emission Emission wavelength for excitation Maximum emission wavelength Maximum excitation wavelength Maximum excitation intensity Maximum emission intensity Stokes shift Table 6 Thermal stabilities of TGA/DTG DTA the monomers and polymers a b c d e f g Compounds T T T (°C) T (°C) T (°C) T (°C) % char Endo (°C) on max 5 10 20 50 DEACIMP 320 367 330 348 359 376 9.5 127, 373 P-DEACIMP 230 270, 425 236 248 269 345 20.0 129 ACIMB 220 302, 478 235 263 351 – 54.0 – P-ACIMB 209 316, 432 216 247 298 424 23.0 – ACIBM 219 244, 419 232 248 315 534 43.0 223 P-ACIBM 201 412, 862 234 298 380 542 35.0 – The onset temperature Temperature of the peak maxima Temperature corresponding to 5% weight loss Temperature corresponding to 10% weight loss Temperature corresponding to 20% weight loss Temperature corresponding to 50% weight loss % char at 1000 °C form. Polymers were prepared by sprinkling on double- SEM photographs of P-DEACIMP, P-ACIBM and sided adhesive tape mounted on a carbon stub and then P-ACIMB are given in Fig. 7. According to the SEM they coated with a thin gold/palladium film by a sputter images, P-ACIBM consists of different, nano-sized parti- coater. cles, while P-ACIMB has sharp edges with the form of 123 Int J Ind Chem (2017) 8:329–343 339 −1 Fig. 6 TGA–DTA–DTG curves of the monomers and polymers (heating rate: 10 C min ;N atmosphere) rods. Surface of P-DEACIMP has the folds in the form of potential. The calculations were performed by using the brain. following equations [24]: E ¼ðÞ 4:39 þ E ð2Þ HOMO ox Electrochemical and conductivity properties E ¼ðÞ 4:39 þ E ð3Þ LUMO red The voltammetric measurements were performed in ace- E ¼ E E : ð4Þ LUMO HOMO tonitrile. All the experiments were performed in a dry box To understand the electronic structure of conjugated filled with Ar at room temperature. The electrochemical polymers it is essential to establish the relative positions of potential of Ag was calibrated with respect to the fer- the characteristic electronic energy levels such as the rocene/ferrocenium (Fc/Fc ) couple. The half-wave 1/2 + highest occupied molecular orbital (HOMO or п level), the potential (E ) of (Fc/Fc ) measured in 0.1 M tetrabuty- lowest unoccupied molecular orbital (LUMO or п), and the lammoniumhexafluorophosphate (TBAPF ) acetonitrile associated energy parameters [25, 26]. solution is 0.39 V with respect to Ag wire or 0.38 V with The oxidation peaks in cyclic voltammograms probably respect to saturated calomel electrolyte (SCE). The correspond to the oxidation of hydroxyl groups to form voltammetric measurements were carried out for all phenoxy radicals. The reduction peaks were presumably monomer compounds by acetonitrile and added to extra due to the reduction of the azomethine linkages via pro- 1 mL DMF for polymers. tonation of azomethine nitrogen [23]. The values of electrochemical band gaps (E ′) are given According to the Table 3, the order of the electro- in Table 3. These data were estimated by using the oxi- chemical band gap values of the polymer changes are as dation onset (E ) and reduction onset (E ) values, as ox red follows: P-ACIBM[P-ACIMB[P-DEACIMP. This was given in Fig. 8 for the compounds where E is the oxi- ox a result of the polyconjugated structures of the polymers, dation peak potential and E is the reduction peak red 123 340 Int J Ind Chem (2017) 8:329–343 Fig. 7 SEM images of polymers which increase HOMO and decrease LUMO energy levels, in a desiccator, and the change in their conductivities resulting in lower electrochemical band gaps [23]. depending on time was measured at specific time intervals Conductivity was measured by a Keithley 2400 Elec- by doping. In the doping process, electron emitting amine trometer (Keithley, Ohio, USA). The pellets were pressed nitrogen and electron pulling iodine coordinate, and the on hydraulic press at 1687.2 kg/cm . Iodine doping was formation of radical cation (polaron) structure in polymer carried out by exposing the pellets to iodine vapor at chain (on amine nitrogen) is enabled [27]. atmospheric pressure and room temperature in a desiccator. Electrical conductivities of the polymers and the chan- Solid-state conductivities of the polymers measured under ges of these values as a function of doping time with iodine air atmosphere were shown in a graph plotted versus time. were determined and shown in Fig. 9. Diaz et al. [28] The measurements for the polymers were carried out in suggested the doping mechanism of Schiff base polymers. pure form and then polymers were exposed to iodine vapor According to doping mechanism, nitrogen, being a very 123 Int J Ind Chem (2017) 8:329–343 341 Fig. 8 Cyclic voltammograms of the monomers and polymers electronegative element, is capable of coordinating with an Conclusions iodine molecule (Scheme 2). Consequently, a charge- transfer complex between imine compound and dopant Schiff base with different position of –OH group was iodine forms and thus conductivity increases [29]. oxidatively polymerized in aqueous alkaline medium by The conductivity values of the undoped P-DEACIMP, NaOCl as oxidant. The structures of the monomers and −8 1 13 P-ACIBM, P-ACIMB polymers were about 4.35 10 , polymers were confirmed by UV–Vis, FT-IR, H, and C −7 −7 −1 1 4.2 9 10 and 5.3 9 10 Scm , respectively. After NMR spectroscopic techniques. According to H-NMR and 120 h doping, the conductivity of P-DEACIMP, P-ACIBM, C-NMR spectra, Schiff bases were polymerized by C–O– −5 P-ACIMB polymers were found to be around 1.78 9 10 , C or C–C binding. Iodine vapor-doped polymer P-DEA- −5 −5 −1 5.13 9 10 and 2.65 9 10 Scm , respectively. CIMP gave the maximum electrical conductivity. The According to these results, increasing of the conductivity synthesized polymers have lower band gaps than the values of polymers were observed as connected iodine monomers because of polyconjugated structures. Accord- doping time. ing to char % at 1000 °C, the thermal stability of the 123 342 Int J Ind Chem (2017) 8:329–343 2. Dineshkumar S, Muthusamy A (2016) Synthesis and spectral characterization of cross linked rigid structured Schiff base polymers: effect of substituent position changes on optical, electrical, and thermal properties. Polym-Plast Technol Eng 55:368–3788 3. El-Shekeil A, Al-Aghbari S (2004) DC electrical conductivity of some oligoazomethines. Polym Int 53:777–788 4. EI-Shekeil A, Hamid S, Ali DA (1997) Synthesis and charac- terization of some polyazomethine conducting polymers and oligomers. Polym Bull 39:1–7 5. Kaya I, Bilici A (2006) Synthesis, characterization and thermal degradation of oligo-2-[(4-hydroxyphenyl) imino-methyl]-1- naphtol and oligomer-metal complexes. J Macromol Sci Part A 43:719–733 6. Kaya I, Bilici A (2007) Synthesis, characterization, thermal analysis, and band gap of oligo-2-methoxy-6-[(4-methylphenyl) imino] methyl phenol. J Appl Polym Sci 104:3417–3426 Fig. 9 Electrical conductivity changes of the polymers I -doped at 2 7. Yao Y, Zhang QT, Tour JM (1998) Synthesis of imine ridged 25 °C planar poly(pyridinethiophene). Combination of planarization and intramolecular charge transfer in conjugated polymers. Macromolecules 31:8600–8606 8. Kaya I, Koc¸a S (2004) Synthesis, characterization and optimum reaction conditions of oligo-2-amino-3-hydroxypyridine and its Schiff base oligomer. Polymer 45:1743–1753 ˘ ˘ 9. Mart H, Yu¨ru¨k H, Sac¸ak M, Muradoglu V, Vilayetoglu AR (2004) The synthesis, characterization and thermal stability of oligo-4-hydroxybenzaldehyde. Polym Degrad Stab 83:395–398 ´ ´ 10. Cimrova V, Ulbricht C, Dzhabarov V, Vyprachticky D, Egbe DM (2014) New electroluminescent carbazole-containing conjugated O polymer: synthesis, photophysics, and electroluminescence. Polymer 55:6220–6226 11. Nishat N, Khan SA, Rasool R, Parveen S (2011) Synthesis, spectral characterization and biocidal activity of thermally stable polymeric Schiff base and its polymer metal complexes. P-ACIBM J Inorg Organomet Polym 21:673–681 12. Ozbu¨lbu¨l A, Mart H, Tunc¸el M, Serin S (2006) A new soluble Scheme 2 The nitrogen atom coordination of iodine to the P-ACIBM Schiff base polymer with a double azomethine group synthesized by oxidative polycondensation. Des Monomers Polym 9:169–179 13. Kaya I, Vilayetoglu AR, Mart H (2001) The synthesis and polymers was in the order P-ACIBM [ P-ACIMB [ P- properties of oligosalicylaldehyde and its Schiff base oligomers. Polymer 42:4859–4865 DEACIMP. The synthesized compounds were all soluble 14. Zhang Y, Shibatomi K, Yamamoto H (2005) Lewis acid cat- in common solvents such as DMF, THF and DMSO. alyzed highly selective halogenation of aromatic compounds. Because of carbazole units in the structures of these Synlett 18:2837–2842 polymers, both conductivity and thermal properties were 15. Kaya I, Aydın A (2012) A new approach for synthesis of elec- troactive phenol based polymer: 4-(2,5-di(thiophen-2-yl)-1H- better than that of other imine polymers in literature. pyrrol-1-yl)phenol and its oxidative polymer. Prog Org Coat Electrochemical band gap values of P-DEACIMP, 73:239–249 P-ACIBM and P-ACIMB were found to be 2.58, 1.54 and 16. Erdik E (2008) Spectroscopic methods in organic chemistry, 5th 2.51 eV, respectively. edn. Gazi Press, Ankara, p 531 17. Ozbu¨lbu¨l A (2006) Synthesis and characterization of new type oligomer Schiff bases with based oligophenol. Master theses, Open Access This article is distributed under the terms of the Institute of Science and Technology, C¸ ukurova University, Creative Commons Attribution 4.0 International License (http://crea Adana, p 108 tivecommons.org/licenses/by/4.0/), which permits unrestricted use, 18. Kaya I, Aydın A (2011) Synthesis and characterization of the distribution, and reproduction in any medium, provided you give poly (amino phenol) derivatives containing thiophene in side appropriate credit to the original author(s) and the source, provide a chain: thermal degradation, electrical conductivity, optical-elec- link to the Creative Commons license, and indicate if changes were trochemical, and fluorescent properties. J Appl Polym Sci made. 121:3028–3040 19. Kaya I, Yıldırım M, Avcı A (2010) Synthesis and characteriza- tion of fluorescent polyphenol species derived from methyl References substituted amino pyridine based Schiff bases: the effect of substituent position on optical, electrical, electrochemical, and 1. Grigoras M, Antonoaia NC (2005) Synthesis and characterization fluorescence properties. Synth Met 160:911–920 of some carbazole-based imine polymers. Eur Polym J 41:1079– 20. Karakaplan M, Demetgu¨l C, Serin S (2008) Synthesis and ther- mal properties of a novel Schiff base oligomer with a double 123 Int J Ind Chem (2017) 8:329–343 343 azomethine group and its Co(II) and Mn(II) complexes. 25. Yang C, Jenekhe S (1995) Conjugated aromatic polyimines. 2. J Macromol Sci Part A 45:406–414 Synthesis, structure, and properties of new aromatic polya- 21. Colladet K, Nicolas M, Goris L, Lutsen L, Vanderzande D (2004) zomethines. Macromolecules 28:1180–1196 Low-band gap polymers for photovoltaic applications. Thin Solid 26. 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Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing carbazole unit

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Abstract

Int J Ind Chem (2017) 8:329–343 DOI 10.1007/s40090-017-0112-5 RESEARCH Synthesis, characterization and electrochemical properties of poly (phenoxy-imine)s containing carbazole unit 1 1 1,2 İsmet Kaya Sebra Çöpür Hatice Karaer · · Received: 29 June 2016 / Accepted: 11 January 2017 / Published online: 27 January 2017 © The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Several new Schiff base polymers were synthe- Keywords Carbazole · Fluorescence · Thermal analysis · sized via oxidative polymerization method in an aqueous Poly(phenoxy-imine) · Band gaps alkaline medium in the presence of NaOCl as an oxidant 1 13 and were confirmed by FT-IR, H-NMR, C-NMR and UV–Vis spectroscopic techniques. Furthermore, cyclic Introduction voltammetry measurements were carried out and the HOMO–LUMO energy levels and electrochemical band Poly(imine)s, known as Schiff base polymers or poly gaps (E ′) were calculated. Additionally, the optical band (azomethine)s or also named polyazines (when hydrazine gaps (E ) were determined using their UV–Vis spectra of is used as diamine compound) [1] which are of great the materials. The morphologic properties of the polymers interest to researchers because of to their potential appli- were investigated by scanning electron microscopy. In cations and advantageous properties. Recently, addition, the number average molecular weight (M ), polyazomethines have attracted much attention of both weight average molecular weight (M ) and polydispersity industries and academia and they have been widely index values of the polymers were determined by gel investigated for their electrochemical properties, thermal permeation chromatography technique. Electrical conduc- stability, fluorescence, intrinsic conductivity [2]. tivity measurements of the doped (with iodine) and Polyimines conjugated polymers have claimed the undoped polymer related to doping time were carried out attention of researchers because of their potentially advan- by four-point probe technique using a Keithley 2400 tageous electronic applications, such as their electrical electrometer. Their thermal behaviors were determined by properties and environmentally stability, with accept- TG–DTA and DSC measurements. The synthesized com- able mechanical strength [3]. Polyazomethines are pounds were soluble in common solvents such as DMF, conducting polymers [4] that usually show an optical THF and DMSO. Photoluminescence properties of the absorption band in the visible region owing to their extended polymers were determined in different concentrations of delocalization of the π electrons along the polymer back- DMF solvent. bone. Upon doping with suitable dopants, charge carriers, namely bipolaron and polaron, are formed in the conjugated backbone. This class of polymers was primarily found to be electroactive as well as semiconductive materials [5, 6], and their conductivity could be increased by doping with a & Ismet Kaya dopant like iodine [2]. Furthermore, Schiff base polymers kayaismet@hotmail.com have been become increasingly interesting in the field of optical materials since they possess great potential for device Polymer Synthesis and Analysis Laboratory, Department applications like light-emitting diodes, photovoltaic cells of Chemistry, C¸ anakkale Onsekiz Mart University, 17020 C¸ anakkale, Turkey and thin film transistors [7]. Poly(azomethine)s including conjugated bonding and Department of Chemistry, Faculty of Sciences, active hydroxyl group have been studied for more than Dicle University, 21280 Diyarbakır, Turkey 123 330 Int J Ind Chem (2017) 8:329–343 60 years, and used in several fields [8]. The oxidative and C-NMR measurements. Thermal stabilities of all polymerization method is simply the reaction of com- compounds were determined by TG–DTA and DSC mea- pounds including –OH groups and active functional groups surements. Also, the conductivity and photoluminescence (–CHO, –NH , –COOH) in their structure with the oxidants (PL) properties of polymers were determined from four- like air oxygen NaOCl, H O an in the aqueous alkaline point probe technique and spectrofluorophotometer mea- 2 2 medium [9]. surements, respectively. Carbazole-containing polymers are of great interest owing to their several potential for applications in organic electronics, such as organic solar cells, organic field effect Experimental transistors (OFET) and organic light-emitting devices (OLED), etc. [10]. Materials In this study, new Schiff bases were synthesized by condensation reaction of 4-diethylaminosalicylaldehyde, 3-Amino-9-ethyl-carbazole, ethyl alcohol, ethyl acetate, 3,4-dihydroxybenzaldehyde and 2,4-dihydroxybenzalde- chloroform, N,N-dimethylacetamide, N,N-dimethylfor- hyde compounds with 3-amino-9-ethyl-carbazole. Then, mamide, dimethyl sulfoxide, acetonitrile and sodium these products were polymerized via oxidative polycon- hypochlorite (NaOCl, 37%) were supplied from Merck densation method in an aqueous alkaline medium in the Chemical Co. (Germany). 4-Diethylamino salicylaldehyde presence of NaOCl as an oxidant. The structures of all (Alfa Aesar), 3,4-dihydroxybenzaldehyde (Fluka) and 2,4- compounds were confirmed by FT-IR, UV–Vis, H-NMR dihydroxybenzaldehyde were supplied from Acros. Scheme 1 Syntheses of Schiff bases and their polymers 123 Int J Ind Chem (2017) 8:329–343 331 Synthesis of the monomers (DEACIMP, ACIMB Characterization techniques and ACIBM) A PerkinElmer spectrum one FT-IR system was used to The synthesis of 5-(diethylamino)-2-[(3-amino-9-ethyl- determine the chemical structure of the monomers and poly- carbazole) imino methyl] phenol (DEACIMP) was syn- mers. Measurements were performed in solid powder form at thesized according to the literature [11] (Scheme 1)as room temperature using universal ATR sampling accessory −1 follows: 4-diethylamino salicylaldehyde (1.77 g) and within the wavelengths of 4000–650 cm .UV–Visspec- 3-amino-9-ethyl-carbazole (1.95 g) were dissolved in troscopy, was used to study the electronic transition in the 20 mL absolute ethanol in two separate beakers, which were then mixed. This mixture was refluxed for 5 h in a two-necked flask and cooled to room temperature. The precipitate formed was filtered, washed with ethanol and then dried under reduced pressure. The same procedure was used to obtain 4-[(3-amino-9-ethyl-carbazole) imino methyl] benzene-1,2-diol (ACIMB) and 4-[(3-amino-9- ethyl-carbazolyl) benzene imine methyl]-1,3-diol (ACIBM) the 3,4-dihydroxybenzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) and 2,4-dihydroxy- benzaldehyde (1.38 g), 3-amino-9-ethyl-carbazole (1.95 g) were used for synthesis the ACIMB and ACIBM, respec- tively. The yields of DEACIMP, ACIMB and ACIBM compounds were found to be 80, 85, 89, respectively. General synthesis procedure of P-DEACIMP, P-ACIMB and P-ACIBM polymers P-DEACIMP, P-ACIMB and P-ACIBM were synthe- sized through the oxidative polycondensation of DEACIMP, ACIMB and ACIBM with aqueous solution of NaOCl (10%). P-DEACIMP was synthesized through oxidative polycondensation of 5-(diethylamino)-2-[(3- amino-9-ethyl-carbazole) imino methyl] phenol using aqueous solution of NaOCl (10%). The 5-(diethy- lamino)-2-[(3-amino-9-ethyl-carbazole) imino methyl] phenol (0.385 g) was dissolved in an aqueous solution of 25 mL KOH (1.0 M) placed into a 100-mL three-necked round-bottom flask, which was fitted with a condenser, thermometer. Furthermore, a funnel containing NaOCl, which was added dropwise over about 30 min, was equipped. The reaction mixture was stirred at 100 °Cfor 24 h, cooled to room temperature and then 25 mL HCl (1.0 M) was added to solution. The P-DEACIMP was washed with water for the separation from mineral salt. The polymers were dried at 60 °Cinanovenfor 24 h [8, 12, 13]. The same procedure was used to obtain the P-ACIMB and P-ACIBM but the 4-[(3-amino-9-ethyl-carbazole) iminemethylbenzene]-1,2-diol (ACIMB) (0.33 g) and 4-[(3-amino-9-ethyl-carbazole) iminomethylbenzene]-1,3- diol (ACIBM) (0.33 g) were used for synthesis the P-ACIMB and P-ACIBM, respectively (Scheme 1). The yields of P-DEACIMP, P-ACIMB and P-ACIBM com- Fig. 1 FT-IR spectra of the monomers and polymers pounds were found to be 70, 72, 76, respectively. 123 332 Int J Ind Chem (2017) 8:329–343 Table 1 FT-IR spectral data of −1 Compounds Wave number (cm ) monomers and polymers –OH C–H (aromatic) C–H (aliphatic) –C=N C=C (aromatic) C–O DEACIMP 3300 2973 2936 1600 1587, 1522 – P-DEACIMP – 2978 2927 1604 1532, 1486 1227 ACIMB 3665 2976 2905 1615 1495, 1473 – P-ACIMB – 2979 2895 1602 1489, 1460 1223 ACIBM 3393 2983 2911 1608 1492, 1476 – P-ACIBM – 2976 2908 1608 1544, 1463 1217 UV–Vis region of the all compounds. Measurements were of the monomers and polymers are shown in Fig. 1. performed by an AnalytikJena Specord 210 Plus with wave- According to these spectra, the characteristic peaks such as length range of 190–900 nm by ethyl alcohol solvent at 25 °C. etheric groups, aromatic and aliphatic C–H stretching 1 13 Hand C NMR spectra (Bruker AV400 FT-NMR spec- peaks are observed, as expected. The peaks related to Ar–O −1 trometer operating at 400.1 and 100.6 MHz, respectively) bonds are in the range of 1217–1235 cm [14], indicating were also recorded in DMSO-d at 25 °C. The tetramethyl- that the polymerization was achieved. The bands due to silane was used as internal standard. Thermal data were hydroxyl groups (–OH) are observed at around 3300– −1 obtained by using a PerkinElmer diamond thermal analysis 3670 cm (Fig. 1)[15]. system. TGA–DTA measurements were performed between Aromatic –CH peaks were observed at around −1 −1 20 and 1000 °C(in N ,rate 10 °Cmin ). DSC analyses of 2980 cm for all the compounds. Furthermore, peaks at −1 polymers were carried out by a PerkinElmer Pyris sapphire 1450–1650 cm were assigned to benzene ring and (C=C) −1 DSC. DSC measurements were conducted between 25 and moiety and those at 1522–1590 cm were attributed to (C– −1 450 °C(in N ,rate 10 °Cmin ). The number average O) stretching [16] while peaks for aliphatic group were −1 molecular weight (M ), weight average molecular weight seen at 2900–2940 cm . −1 (M ) and polydispersity index (PDI) were determined by gel The peak at 1600–1620 cm corresponds to –CH=N permeation chromatography-light scattering (GPC-LS) stretching vibration of imine moiety. The peaks of vibra- device by Malvern Viscotek GPC Dual 270 max. For GPC tion bonding are also shown in Table 1. As seen in Fig. 1, investigations a medium 300 9 8.00 mm dual column light peaks of polymers were broader than that of monomers scattering detector (LS) and a refractive index detector (RID) after the polycondensation reaction owing to their poly- were used to analyze the products at 55 °C. LiBr (40 mM) was conjugated structures. Other characteristic absorption added to the DMF mobile phase to dissociate molecular bands are also presented in Table 1. aggregates of polymer during GPC analysis. Surface mor- Furthermore, the edged peaks of P-DEACIMP, phology of the polymers was determined by scanning electron P-ACIMB and P-ACIBM were broader and decreased microscope (SEM) (JEOL, JSM-7100 model). Cyclic numerically due to the increase in molecular weight after voltammetry (CV) measurements were carried out with a CH polymerization reactions [17], confirming polymerization 660 C Electrochemical Analyzer (CH Instruments, Texas, of DEACIMP, ACIMB and ACIBM. 1 13 USA) at a potential scan rate of 20 mV/s. A Shimadzu RF- H NMR and C NMR spectra of the monomers and 5301PC spectrofluorophotometer was used in fluorescence polymers were recorded in DMSO-d . Hdataof the measurements. Emission spectra of the synthesized polymers monomers and polymers are listed in Table 2 and the were obtained in different concentration of DMF solvent. spectrum of a representative polymer P-DEACIMP and 1 13 Also, to obtain maximal emission intensity values of polymers DEACIMP are shown in Fig. 2.The Hand CNMR were investigated in different concentrations of DMF spectra of DEACIMP and P-DEACIMP data are given in 1 13 solutions. Figs. 2 and 3. Hand C NMR data results of the synthe- sized compounds are listed in Table 2 except for DEACIMP and P-DEACIMP. When phenol-based Schiff bases were Results and discussion polymerized by oxidative polycondensation, they were combined by C–C binding at ortho and/or para position of Structural characterization of the monomers the ring or alternatively C–O–C binding through oxygen and polymers atom of –OH moiety (Scheme 1)[2, 18]. H-NMR spectra of the polymers contained three types of signals assigned as The structures of the monomers and polymers were con- follows: the singlet at 8.05–8.98 ppm, –CH=N–; the multiple 1 13 firmed by FT-IR, H and C-NMR spectra. FT-IR spectra at 6.40–8.50 ppm, aromatic protons. The proton resonances 123 Int J Ind Chem (2017) 8:329–343 333 Table 2 NMR spectra data of the monomers and polymers Compounds NMR spectra data H NMR (DMSO-d , ppm, δ): 10.25 and 14.08 (s, –OH), 1.30 (t, Ar–He), 4.43 (m, Ar–Hd), 6.48–8.20 (m, Ar–H), 8.25 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 118 (C1-H), 121 (C2-H and C3-H), 126 (C4-ipso), 133 (C5-ipso), 109 (C6-H), 107 (C7-ipso), 138 (C8-ipso), 38 (C9-H), 14 (C10- H), 112 (C11-H), 160 (C12-ipso), 162 (C13-H), 139 (C14-ipso), 156 (C15-H), 140 (C16-H), 161 (C17-ipso), 129 (C18-H), 115 (C19-H), 122 (C20-H and C21- H) H NMR (DMSO-d , ppm, δ): 11.02 and 13.20 (s, –OH), 1.27 (t, Ar–He), 4.38 (q, Ar–Hd), 7.40–8.03 (m, Ar–H), 8.05 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 133 (C1-H), 110 (C2-H), 121 (C3-H), 118 (C4-H), 120 (C5-H), 126 (C6-ipso), 105 (C7-ipso), 135 (C8-ipso), 36 (C9-H), 14 (C10- H), 111 (C11-H), 160 (C12-ipso), 165 (C13-H), 118 (C14-ipso), 107 (C15-H), 126 (C16-ipso), 161 (C17-ipso), 123 (C18-ipso), 139 (C19-ipso), 125 (C20-H), 112 (C23-H) H NMR (DMSO-d , ppm, δ): 10.24 and 14.07 (s, –OH), 1.31 (t, Ar–He), 4.45 (m, Ar–Hd), 6.48–8.20 (m, Ar–H), 8.96 (s, –CH=N) C NMR (DMSO-d , ppm, δ): 121 (C1-H), 119 (C2-H), 122 (C3-H and C4-H), 126 (C5-ipso), 109 (C6-H), 102 (C7-ipso), 133 (C8-ipso), 39 (C9-H), 15 (C10- H), 112 (C11-H), 140 (C12-ipso), 160 (C13-H), 118 (C14-ipso), 162 (C15-ipso and C18-ipso), 107 (C16-H), 118 (C17-H), 109 (C19-H), 121 (C20-H) H NMR (DMSO-d , ppm,) δ): 11.00 and 13.00 (s, –OH), 7.22–8.33 (m, Aromatic protons), 8.87 (s, –CH=N), 1.30 (t, Ar–He), 4.43 (m, Ar–Hd). C NMR (DMSO-d , ppm, δ): 126 (C1-ipso), 107 (C2-H), 120 (C3-H), 116 (C4-H), 120 (C5-H), 125 (C6-ipso), 103 (C7-ipso), 127 (C8-ipso), 40 (C9-H), 14 (C10-ipso), 112 (C11-H), 140 (C12-ipso), 160 (C13-H), 110 (C14-ipso), 129 (C15-H), 116 (C16-ipso), 164 (C17-ipso), 126 (C18-ipso), 156 (C19-ipso), 112 (C20-H), 125 (C21-H) of hydroxyl (–OH) groups were observed at 12.01, 10.25 The azomethine protons are observed in 8.84, 8.25 and and 14.08, 10.24 and 14.07 ppm for DEACIMP, ACIMB 8.96 ppm for DEACIMP, ACIMB and ACIBM monomers, and ACIBM, respectively. The proton signal of hydroxyl (– 8.90, 8.05 and 8.87 ppm for P-DEACIMP, P-ACIMB and OH) groups were observed at 12.85, 11.02 and 13.20, 11.00 P-ACIBM polymers, respectively. The H NMR spectra of and 13.00 ppm for P-DEACIMP, P-ACIMB and P-ACIBM, polymers shows broad signals for aromatic protons which respectively. Meanwhile, the FT-IR spectra of polymers confirm the participation of aromatic ring in polymeriza- −1 show bands in 1217, 1223 and 1227 cm is assignable to tion [2, 19]. New signals were observed in the region of the phenolic C–O stretching vibration [2]. 169, 162 and 168 ppm in the C NMR spectra of 123 334 Int J Ind Chem (2017) 8:329–343 Fig. 2 H NMR spectra of DEACIMP and P-DEACIMP P-DEACIMP, P-ACIMB and P-ACIBM, respectively, due according to a polystyrene standard calibration curve. The to –C–O–C– coupling, confirming polymerization occurred weight average molecular weight (M ) and polydispersity via –OH moiety [20]. index (PDI, M /M ) values of P-DEACIMP, P-ACIBM and w n Appearance of the new short resonances at 109,148 and P-ACIMB were found to be 8350, 6400, and 9200 and 1.25, 135,139 ppm obviously indicate polymerization of DEA- 1.22 and 1.27, respectively. These results also agree with the CIMP, ACIMB and ACIBM, respectively, i.e., –C–C solubility tests. P-ACIBM had lower molecular weight than binding occurs at ortho or para position of phenol by distri- P-DEACIMP and P-ACIMB polymers. So it was a fine-soluble bution of the phenoxy radical to the ring. The azomethine and polymer in common organic solvents and the others had lower aromatic carbon signals were observed at 159 and 97–163, solubilities owing to their high-molecular weighted structures. 162 and 107–161, 160 and 102–162 ppm in the CNMR spectra of DEACIMP, ACIMB and ACIBM, respectively. Optical properties of compounds Thus, we can easily conclude that the NMR data confirming the structures of the aimed products. UV–Vis spectra of the compounds recorded in ethyl alco- hol at room temperature are given in Fig. 4. Their optical GPC analysis of polymers band gaps (E ) were calculated as in the literature [21] and results are shown in Table 3. Gel permeation chromatography (GPC) analyses of com- E ¼ 1242=k ; ð1Þ g onset pounds (P-DEACIMP, P-ACIBM and P-ACIMB) were where λ is the onset wavelength which may be deter- performed at 55 °C by DMF as eluent at a flow rate of onset −1 mined by intersection of two tangents on the absorption 1.0 mL min . The number average molecular weight (M ), edges. λ also indicates the electronic transition start weight average molecular weight (M ) and polydispersity onset wavelength. According to results, one can easily conclude index (PDI, M /M ) values of compounds were calculated w n 123 Int J Ind Chem (2017) 8:329–343 335 Fig. 3 C NMR spectra of DEACIMP and P-DEACIMP −1 Fig. 4 Absorption spectra of the monomers and polymers (conc.: 100 mg L in ethyl alcohol solvent) that the polymers have low optical band gaps. Because of It is known that the solubility behavior is very advan- monomers and polymers compounds to be having the same tageous for the processing of these materials for functional groups, some UV–Vis absorption bands of their technological applications [4]. Thus, the solubility prop- were observed as similar. erties of the polymers and monomers were tested in 123 336 Int J Ind Chem (2017) 8:329–343 Table 3 Optical electronic a b c d e f Compound E (eV) λ (nm) E (eV) E (eV) HOMO (eV) LUMO (eV) E ′ (eV) g onset ox red g structure parameters of the monomers and polymers DEACIMP 2.43 510 1.44 −1.73 −5.83 −2.66 3.17 P-DEACIMP 2.41 515 1.28 −1.30 −5.67 −3.09 2.58 ACIMB 2.60 478 1.32 −1.29 −5.71 −3.10 2.60 P-ACIMB 3.13 396 1.29 −1.23 −5.68 −3.16 2.51 ACIBM 3.05 406 0.92 −1.33 −5.31 −3.06 2.25 P-ACIBM 3.01 412 0.80 −0.74 −5.19 −3.65 1.54 Optical band gap Oxidation peak potential Reduced peak potential Highest occupied molecular orbital Lowest unoccupied molecular orbital Electrochemical band gap Table 4 Solubility Solvent DEACIMP ACIMB ACIBM P-DEACIMP P-ACIMB P-ACIBM characteristics of the monomers −1 and polymers (1 mg mL )at DMF ++ + + + + 25 °C DMA ++ + + + + DMSO ++ + + + + THF ++ + + + + Ethyl acetate ++ + ⊥ −− Chloroform ++ + ⊥⊥ ⊥ Acetone ++ + ⊥⊥ ⊥ Ethanol ++ + ⊥⊥ ⊥ Acetonitrile ++ + ⊥⊥ + (+), soluble; (⊥), partially soluble; (−), insoluble different solvents by using 1 mg of compound in 1 mL significant conformational differences between ground solvent and shown in Table 4. state (S ) and the first excited state (S ). If the Δλ value is 0 1 ST Fluorescence properties of the synthesized compounds too small, the emission and excitation spectra will overlap are determined using DMF solutions at different concen- more. So the emitted light will be self-absorbed and the trations [22]. Also, the optimization of the concentrations photoluminescence efficiency will decrease. Δλ values ST to obtain maximal emission intensity is investigated in are listed in Table 5. Δλ values of P-DEACIMP, ST DMF. Concentration effects on the fluorescence properties P-ACIMB and P-ACIBM are calculated as 48, 31 and 61, are shown in Fig. 5. Maximum emission intensity values of respectively. According to Δλ values, the synthesized ST the compounds are also given in Table 5. When concen- P-ACIBM can be used for the production of fluorescence tration of DEACIMP, P-DEACIMP, ACIMB were sensor owing to high Δλ value [23]. It can be seen from ST decreased, they showed bathochromic shift in the range Fig. 5 that with increase in the concentrations of the 14–35 nm. On the other hand, a significant change in the solutions, the absorption spectra of the compounds were emission wavelength of these polymers was not observed. observed to shift to the visible region. As seen in Table 5, these results showed that P-ACIMB polymer has higher emission intensity values at Thermal properties of the polymers −6 −5 −1 9.76 9 10 and 1.95 9 10 gmL than the other syn- thesized polymers and monomers. But P-DEACIMP and Thermal degradation data (TGA–DTA and DTG) are listed ACIBM have the lowest emission intensity as polymer and in Table 6. TGA curves of the synthesized monomers and monomer, respectively. polymers are also shown in Fig. 6. According to the TGA Stokes shift (Δλ ) is the difference between positions of results, the initial degradation temperatures (T ) of the ST on the band maxima of emission and excitation spectra of the monomers are higher than their polymers, expect for same electronic transition. This knowledge offers P-ACIBM. This could be explained by the formation of C– 123 Int J Ind Chem (2017) 8:329–343 337 Fig. 5 Emission spectra of the synthesized monomers and polymers in different concentrations (PL intensity photoluminescence intensity, slit width: 3 nm, in DMF solvent) O etheric bond during polymerization. This weak bond is were 23, 16; 21 and 35% at these steps, respectively. easily broken at mild temperatures and makes the polymer P-DEACIMP, P-ACIMB and P-ACIBM polymers were thermally unstable [21, 22]. Furthermore, when % char degraded in two steps: between 230–370, 209–380 and amounts are compared, % char of ACIMB was higher than 201–620 for the first step; 370–570, 380–600 and 620– other compounds at 1000 °C. In addition, Table 6 exhibits 1000 °C for the second step and their weight losses were listed temperatures corresponding to 5, 10, 20 and 50% 53, 37, 50; 25, 22 and 14% at these steps, respectively. weight losses of the all compounds. T values of mono- According to DSC measurements of polymers, the T on g mers and polymers were found between 219–320 and 201– and C values of P-DEACIMP, P-ACIMB, and P-ACIBM 230 °C, respectively. According to TG curves of ACIMB, were found to be 123, 105 and 104 °C and 2.083, 0.086, −1 −1 ACIBM, P-DEACIMP, P-ACIMB, and P-ACIBM, the and 0.075 J g K , respectively. The results indicated that losses of absorbed water were found to be 2, 1.7, 2.7, 5.1 P-DEACIMP has the highest T . and 3.9%, respectively, between 20 and 150 °C. DEACIMP monomer was degraded at the one step between 320 and Morphologic properties 540 °C and its weight loss was 86.5% at this step. ACIMB and ACIBM monomers were degraded in two steps: Morphological properties of the polymers are obtained by between 220–385 and 219–308 for the first step; 385–690 SEM technique. SEM images of compounds were recorded and 308–665 °C for the second step and their weight losses using a Jeol JSM-7100F Schottky instrument in a powder 123 338 Int J Ind Chem (2017) 8:329–343 Table 5 The maximum emission intensity values that obtained from fluorescence spectra of the monomers and polymers as a function of concentration −1 a b c d e f g Compounds Concentration (mg mL ) ƛ (nm) ƛ (nm) ƛ (nm) ƛ (nm) Ι Ι Δƛ ex em max(ex) max(em) ex em ST −5 DEACIMP 6.250 9 10 460 496 450 495 305 260 35 −5 3.125 9 10 460 496 467 495 378 332 35 −5 1.563 9 10 460 496 473 495 412 140 35 −3 P-DEACIMP 1.250 9 10 513 555 498 561 272 200 48 −4 6.250 9 10 513 555 512 561 264 258 48 −4 3.125 9 10 513 555 532 561 247 34 48 −4 ACIMB 6.250 9 10 475 514 460 515 243 117 60 −4 3.125 9 10 475 514 474 515 237 241 60 −4 1.563 9 10 475 514 484 515 233 204 60 −5 P-ACIMB 3.90 9 10 416 478 385 447 574 302 31 −5 1.95 9 10 416 478 380 447 [1000 338 31 −6 9.75 9 10 416 478 375 447 [1000 317 31 −3 ACIBM 2.250 9 10 528 568 526 561 233 204 33 −3 1.125 9 10 528 568 519 561 237 117 33 −4 5.625 9 10 528 568 518 561 243 241 33 −4 P-ACIBM 7.80 9 10 384 449 381 445 224 589 61 −4 3.90 9 10 384 449 380 445 602 586 61 −4 1.95 9 10 384 449 379 445 572 558 61 Excitation wavelength for emission Emission wavelength for excitation Maximum emission wavelength Maximum excitation wavelength Maximum excitation intensity Maximum emission intensity Stokes shift Table 6 Thermal stabilities of TGA/DTG DTA the monomers and polymers a b c d e f g Compounds T T T (°C) T (°C) T (°C) T (°C) % char Endo (°C) on max 5 10 20 50 DEACIMP 320 367 330 348 359 376 9.5 127, 373 P-DEACIMP 230 270, 425 236 248 269 345 20.0 129 ACIMB 220 302, 478 235 263 351 – 54.0 – P-ACIMB 209 316, 432 216 247 298 424 23.0 – ACIBM 219 244, 419 232 248 315 534 43.0 223 P-ACIBM 201 412, 862 234 298 380 542 35.0 – The onset temperature Temperature of the peak maxima Temperature corresponding to 5% weight loss Temperature corresponding to 10% weight loss Temperature corresponding to 20% weight loss Temperature corresponding to 50% weight loss % char at 1000 °C form. Polymers were prepared by sprinkling on double- SEM photographs of P-DEACIMP, P-ACIBM and sided adhesive tape mounted on a carbon stub and then P-ACIMB are given in Fig. 7. According to the SEM they coated with a thin gold/palladium film by a sputter images, P-ACIBM consists of different, nano-sized parti- coater. cles, while P-ACIMB has sharp edges with the form of 123 Int J Ind Chem (2017) 8:329–343 339 −1 Fig. 6 TGA–DTA–DTG curves of the monomers and polymers (heating rate: 10 C min ;N atmosphere) rods. Surface of P-DEACIMP has the folds in the form of potential. The calculations were performed by using the brain. following equations [24]: E ¼ðÞ 4:39 þ E ð2Þ HOMO ox Electrochemical and conductivity properties E ¼ðÞ 4:39 þ E ð3Þ LUMO red The voltammetric measurements were performed in ace- E ¼ E E : ð4Þ LUMO HOMO tonitrile. All the experiments were performed in a dry box To understand the electronic structure of conjugated filled with Ar at room temperature. The electrochemical polymers it is essential to establish the relative positions of potential of Ag was calibrated with respect to the fer- the characteristic electronic energy levels such as the rocene/ferrocenium (Fc/Fc ) couple. The half-wave 1/2 + highest occupied molecular orbital (HOMO or п level), the potential (E ) of (Fc/Fc ) measured in 0.1 M tetrabuty- lowest unoccupied molecular orbital (LUMO or п), and the lammoniumhexafluorophosphate (TBAPF ) acetonitrile associated energy parameters [25, 26]. solution is 0.39 V with respect to Ag wire or 0.38 V with The oxidation peaks in cyclic voltammograms probably respect to saturated calomel electrolyte (SCE). The correspond to the oxidation of hydroxyl groups to form voltammetric measurements were carried out for all phenoxy radicals. The reduction peaks were presumably monomer compounds by acetonitrile and added to extra due to the reduction of the azomethine linkages via pro- 1 mL DMF for polymers. tonation of azomethine nitrogen [23]. The values of electrochemical band gaps (E ′) are given According to the Table 3, the order of the electro- in Table 3. These data were estimated by using the oxi- chemical band gap values of the polymer changes are as dation onset (E ) and reduction onset (E ) values, as ox red follows: P-ACIBM[P-ACIMB[P-DEACIMP. This was given in Fig. 8 for the compounds where E is the oxi- ox a result of the polyconjugated structures of the polymers, dation peak potential and E is the reduction peak red 123 340 Int J Ind Chem (2017) 8:329–343 Fig. 7 SEM images of polymers which increase HOMO and decrease LUMO energy levels, in a desiccator, and the change in their conductivities resulting in lower electrochemical band gaps [23]. depending on time was measured at specific time intervals Conductivity was measured by a Keithley 2400 Elec- by doping. In the doping process, electron emitting amine trometer (Keithley, Ohio, USA). The pellets were pressed nitrogen and electron pulling iodine coordinate, and the on hydraulic press at 1687.2 kg/cm . Iodine doping was formation of radical cation (polaron) structure in polymer carried out by exposing the pellets to iodine vapor at chain (on amine nitrogen) is enabled [27]. atmospheric pressure and room temperature in a desiccator. Electrical conductivities of the polymers and the chan- Solid-state conductivities of the polymers measured under ges of these values as a function of doping time with iodine air atmosphere were shown in a graph plotted versus time. were determined and shown in Fig. 9. Diaz et al. [28] The measurements for the polymers were carried out in suggested the doping mechanism of Schiff base polymers. pure form and then polymers were exposed to iodine vapor According to doping mechanism, nitrogen, being a very 123 Int J Ind Chem (2017) 8:329–343 341 Fig. 8 Cyclic voltammograms of the monomers and polymers electronegative element, is capable of coordinating with an Conclusions iodine molecule (Scheme 2). Consequently, a charge- transfer complex between imine compound and dopant Schiff base with different position of –OH group was iodine forms and thus conductivity increases [29]. oxidatively polymerized in aqueous alkaline medium by The conductivity values of the undoped P-DEACIMP, NaOCl as oxidant. The structures of the monomers and −8 1 13 P-ACIBM, P-ACIMB polymers were about 4.35 10 , polymers were confirmed by UV–Vis, FT-IR, H, and C −7 −7 −1 1 4.2 9 10 and 5.3 9 10 Scm , respectively. After NMR spectroscopic techniques. According to H-NMR and 120 h doping, the conductivity of P-DEACIMP, P-ACIBM, C-NMR spectra, Schiff bases were polymerized by C–O– −5 P-ACIMB polymers were found to be around 1.78 9 10 , C or C–C binding. Iodine vapor-doped polymer P-DEA- −5 −5 −1 5.13 9 10 and 2.65 9 10 Scm , respectively. CIMP gave the maximum electrical conductivity. 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Journal

International Journal of Industrial ChemistrySpringer Journals

Published: Jan 27, 2017

References