Res. Chem. Intermed.
, Vol. 27, No. 1,2, pp. 177–187 (2001)
Direct observation of interfacial hole transfer from
a photoexcited TiO
particle to an adsorbed molecule
by femtosecond diffuse re ectance spectroscopy
, TSUYOSHI ASAHI
, HIROSHI MASUHARA
and MASAKAZU ANPO
Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture,
Gakuen-cho 1-1, Sakai, Osaka 599-8531, Japan
Received 17 March 2000; accepted 13 July 2000
Abstract—On the basis of transient absorption spectral measurements in the whole visible region
using femtosecond diffuse re ectance spectroscopy, a hole transfer process from photoexcited TiO
to an adsorbed molecule SCN
was elucidated. In a TiO
aqueous suspension with KSCN, absorption
rise of dimer radical anion (SCN)
was observed indicating hole transfer. Interestingly, there were
two rise components with <1 ps and several 100 ps, which were shorter in lower pH of the solution.
Ultrafast hole transfer and subsequent intermolecular geometrical change of a dimmer radical anion
are also discussed.
is attracting much interest as a high reactive, stable and safe photocatalyst,
and its mechanism has been investigated widely by using of various methods such
as photochemical product analysis, electrochemical voltammetry, IR spectroscopy,
scanning probe microscopy, and time-resolved uorescence or absorption spec-
troscopy [1 –5]. To investigate the ultrafast primary events, time-resolved spec-
troscopy is very powerful, which has a time resolution of femtosecond nowadays.
As for UV-visible transient absorption measurements, transmittance-mode spec-
troscopy has been in general but only applicable to transparent samples like so-
lutions and lms, which are generally easy to measure due to a simple optical
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