Spin polarization mechanisms in early stages of photoinduced charge separation in surface-modified TiO2 nanoparticles

Steady-state and time-resolved electron paramagnetic resonance (EPR) experi ments reveal that photoinduced charge separation in surface-modified nanopa rticles yields interacting electron-hole radical pairs with spectral featur es indicative of a range of dynamic properties (Radical Pair Model and emis sive Triplet Model CIDEP). Fast exchange in the radical pair is indicated b y the presence of a central line at the midpoint, (g(ave) = (g(h) + g(e))/2 ), of electron and hole g-factors. Excess emission is consistent with the t riplet character of the exciton precursor. A subset of electron-hole radica l pairs exhibits the spin feature characteristic of correlated radical pair polarization (CRPP) reflecting a weak interaction between photogenerated h oles and electrons. (C) 2001 Published by Elsevier Science B.V.