Spacer length dependence of photoinduced electron transfer in heterosupramolecular assemblies of TiO2 nanoparticles and terthiophene

Heterosupramolecular assemblies of TiO2 nanoparticles ( <3 nm) and a fluorescent conjugated terthiophene oligomer, connected via saturated spacers of 5, 9, and 13 single bonds, have been prepared and used to investigate the distance dependence of photoinduced charge transfer in hybrid organic - inorganic systems. In chloroform, the rate for charge transfer in these oligomer - TiO2 conjugates decreases with increasing spacer length from 2.5 x 10(10) to 1.6 x 10(9) s(-1). Hence, charge transfer is relatively fast even for the longest linker. The rate constant does not follow a simple exponential decay with spacer length and the logarithmic attenuation per bond is relatively low (0.3 < beta < 0.6). This effect is discussed in terms of back folding or amplification of the electronic coupling by proximate alkyl chains on the surface of the nanoparticle.