Theoretical study on the surface complex between TiO2 and hetero-TCNQ

Interfacial charge transfer transitions between organic and inorganic materials are expected to be a potential photoinduced charge separation mechanism for photoenergy conversions. Recently, we have reported that the hybrid material formed from TiO$_2$ nanoparticles and an organic electron acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), shows strong interfacial charge transfer absorption in the visible region [1-3]. In the present work, we have investigated the molecular and optical properties of the surface complexes of TiO$_2$ and hetero-TCNQ: furan-TCNQ, thiophene-TCNQ, and selenophene-TCNQ, which are considered to promote light absorption in the near-IR region more efficiently than TiO$_2$-TCNQ. The redox potentials of these hetero-TCNQ are calculated to be lower than that of TCNQ. We calculated these hetero-TCNQ and the surface complexes between those and a TiO$_2$ nano cluster, using the density functional theory (DFT) and time-dependent DFT methods. [1] R. Jono, J. Fujisawa, H. Segawa, and K. Yamashita, J. Phys. Chem. Lett., 2, 1167-1170 (2011). [2] S. Manzhos, R. Jono, K. Yamashita, J. Fujisawa, M. Nagata, and H. Segawa, J. Phys. Chem. C, 115, 21487-21493 (2011). [3] R. Jono, J. Fujisawa, H. Segawa, and K. Yamashita, Phys. Chem. Chem. Phys., 15, 18584-18588 (2013).