Theoretical Study of Surface Complexes between TiO2 and HeteroTCNQs Showing Interfacial Charge-Transfer Transitions Designed Based on Redox Potential

TiO2-heteroTCNQ surface complexes between TiO2 and 2,5-bis(dicyanomethylene)-2,5-dihydrofuran, 2,5-bis(dicyanomethylene)-2,5-dihydrothiophene, and 2,5-bis(dicyanomethylene)-2,5-dihydroselenophene (furanTCNQ, thiopheneTCNQ, and selenopheneTCNQ, respectively) were designed using the redox potential of heteroTCNQ molecules. The tendency of the calculated redox potentials was in good agreement with the experimental results. We assumed the chemical adsorption structure of the TiO2-heteroTCNQ surface complexes that formed an O-C bond as well as that of previously reported TiO2-TCNQ surface complex. These surface complexes showed light absorption in the visible to near-IR region via interfacial charge-transfer transitions at longer wavelengths, as assessed using a TD-DFT calculation. This indicates that these surface complexes, as well as the TiO2-TCNQ surface complex, are applicable to the development of solar cells.