Res. Chem. Intermed.
, Vol. 34, Nos 5–7, pp. 551–564 (2008)
Koninklijke Brill NV, Leiden, 2008.
Also available online - www.brill.nl/rci
Charge separation in mesoporous aluminosilicates
, MICHAEL N. PADDON-ROW
RUSSELL F. HOWE
School of Chemistry, University of New South Wales, Sydney NSW 2052, Australia
Chemistry Department, University of Aberdeen, Aberdeen AB24 3UE, UK
Received 30 November 2006; accepted 11 February 2007
Abstract—EPR spectroscopy has been used to investigate spontaneous and/or photo-induced elec-
tron transfer between adsorbed organic molecules and the mesoporous aluminosilicate MCM-41
host. Spontaneous electron transfer occurs from the host to electron acceptor molecules with suf-
ﬁciently favourable reduction potentials (TCNE, TCNQ, 1,4-benzoquinone, 1,4-naphthaquinone and
1,4-anthraquinone), provided the MCM-41 contains aluminium and the radical anion yield correlates
with the aluminium content of the host. The semiquinone radical anions are interacting strongly with
sites, whereas the TCNE and TCNQ radical anions are loosely bound and can be washed
from the host. Radical cation formation is observed when electron donor molecules with favourable
oxidation potentials are adsorbed in MCM-41 containing aluminium, and the radical cations formed
interact with exposed Al
sites. This work shows that aluminium-containing MCM-41 contains
both electron donating and electron accepting sites which may intervene in intra-molecular charge
separation processes in adsorbed organic molecules.
Keywords: EPR; MCM-41; electron transfer; radical cation; radical anion.
The design of chemical systems for artiﬁcial photosynthesis, the conversion of
photon energy into useful redox potentials, has attracted considerable attention
for more than 20 years [1– 9]. One of the central issues for the efﬁciency of
photocatalysis and solar photovoltaic cells to utilize solar energy is to achieve
efﬁcient hole–electron charge separation with long life time. One approach taken
to solve this problem has been the design of donor–acceptor dyad molecules in
which an electron produced at the electron donor chromophore end of the molecule
travels rapidly to the electron acceptor end. A charge separated state is then achieved
provided the back electron transfer processes can be inhibited [5, 9].
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