Photo-Gated Intervalence Charge Transfer of Ethynylferrocene Functionalized Titanium Dioxide Nanoparticles

Abstract Ethynylferrocene-functionalized titanium dioxide nanoparticles (TiO 2 -eFc) were synthesized, for the first time ever, by a modified two-phase hydrothermal method. Transmission electron microscopic measurements showed that the nanoparticles were rather uniform in size, with an average diameter of 4.0 ± 0.5 nm and well-defined lattice fringes that were consistent with those of anatase TiO 2 . 1 H NMR, FTIR and XPS measurements confirmed the attachment of the ferrocenyl ligands onto the nanoparticle surface, most likely forming Ti−C C−Fc interfacial bonds. The resulting nanoparticles exhibited a bandgap of ca. 3.3 eV, and two emission bands in photoluminescence measurements at 351 and 460 nm, with the former due to the TiO 2 cores whereas the latter from intraparticle charge delocalization between the nanoparticle-bound acetylene moieties under UV photoirradiation. In electrochemical measurements, only one pair of voltammetric peaks were observed in the dark, due to the redox reactions of the nanoparticle-bound ferrocenyl groups. However, when subject to photoirradiation with UV lights (254 and 365 nm), two pairs of voltammetric peaks appeared, with a respective peak spacing of 174 and 198 mV, suggesting intervalence charge transfer (IVCT) between the ferrocenyl moieties bound on the nanoparticle surface. This arose from photo-enhanced electrical conductivity of the TiO 2 cores that served as part of the chemical linkage bridging the ferrocenyl moieties. Significantly, such photo-gated IVCT varied with the photoexcitation energy that dictated the intraparticle charge transfer pathways.