The effect of group-substitution on the sensitization properties of alkynylrhenium(I) tricarbonyl diimine complexes adsorbed to TiO 2 (101) film surface: a theoretical study

A series of dyes are designed by adding the different electron-donating (–CH3, –NH2, –OH) and electron-withdrawing groups (–Br, –Cl, –NO2) to the different ancillary ligands in the alkynylrhenium(I) tricarbonyl diimine complexes [Re(CO)3(N^N){C≡C–C6H4–CH=C(CN)(COOH)}], where N^N = 1,10-phenanthroline (phen)(1) and then investigated the sensitization properties of dyes linked to the TiO2(101) surface. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the electronic structure, frontier molecular orbitals, and absorption spectral properties. The effect of group-substitution on sensitization properties is obvious. When the dye molecules are combined with TiO2(101) surface, not only the absorptions of some sensitizers containing –CH3 or –OH groups have red shift but also the electrons can be directly injected into the TiO2 conduction band from the dye molecules compared with the parent molecular 1. The results indicate that the designed dyes containing electron-donating groups have smaller energy gaps, better light-harvesting efficiency, sufficient driving force, and higher charge transfer efficiency as appropriate dye sensitizers. We hope it can provide valuable hints so that we can design more efficient dye sensitizers in DSSCs.