Nanoparticle-Mediated Intervalence Charge Transfer: Core-Size Effects.

Two types of platinum nanoparticles (NPs) functionalized with ethynylferrocene were prepared. The subnanometer-sized NPs (Pt10eFc) showed semiconductor-like characteristics with a bandgap of about 1.0 eV, and the other was metal-like with a core size of about 2 nm (Pt314eFc) and no significant bandgap. IR spectroscopic measurements showed a clear red-shift of the C≡C and ferrocenyl ring =C-H vibrational energies with increasing particle core size owing to enhanced intraparticle charge delocalization between the particle-bound ferrocenyl moieties. Electrochemical measurements showed two pairs of voltammetric peaks owing to intervalence charge transfer between the ferrocenyl groups on the nanoparticle surface, which was apparently weaker with Pt10 eFc than with Pt314 eFc. Significantly, the former might be markedly enhanced with UV photoirradiation owing to enhanced nanoparticle electronic conductivity, whereas no apparent effects were observed with the latter.