Interfacial Electron Transfer into Functionalized Crystalline Polyoxotitanate Nanoclusters

Interfacial electron transfer (IET) between a chromophore
and a
semiconductor nanoparticle is one of the key processes in a dye-sensitized
solar cell. Theoretical simulations of the electron transfer in polyoxotitanate
nanoclusters Ti17O24(OPri)20 (Ti17) functionalized with
four p-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established
by X-ray diffraction measurements, are presented. Complementary experimental
information showing IET has been obtained by EPR spectroscopy. Evolution
of the time-dependent photoexcited electron during the initial 5 fs
after instantaneous excitation to the NPA LUMO + 1 has
been evaluated. Evidence for delocalization of the excitation over
multiple chromophores after excitation to the NPA LUMO
+ 2 state on a 15 fs time scale is also obtained. While chromophores
are generally considered electronically isolated with respect to neighboring
sensitizers, our calculations show that this is not necessarily the
case. The present work is the most comprehensive study to date of
a sensitized semiconductor nanoparticle in which the structure of
the surface and the mode of molecular adsorption are precisely defined.