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

Steady-state and time-resolved electron paramagnetic resonance (EPR) experiments reveal that photoinduced charge separation in surface-modified nanoparticles yields interacting electron–hole radical pairs with spectral features indicative of a range of dynamic properties (Radical Pair Model and emissive Triplet Model CIDEP). Fast exchange in the radical pair is indicated by the presence of a central line at the midpoint, (gave=(gh+ge)/2) , of electron and hole g-factors. Excess emission is consistent with the triplet character of the exciton precursor. A subset of electron–hole radical pairs exhibits the spin feature characteristic of correlated radical pair polarization (CRPP) reflecting a weak interaction between photogenerated holes and electrons.