Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies

Values of charge transfer integrals, spatial overlap integrals and site energies involved in transport of positive charges along columnar stacked triphenylene derivatives are provided. These parameters were calculated directly as the matrix elements of the Kohn-Sham Hamiltonian, defined in terms of the molecular orbitals on individual triphenylene molecules. This was realized by exploiting the unique feature of the Amsterdam density functional theory program that allows one to use molecular orbitals on individual molecules as a basis set in calculations on a system composed of two or more molecules. The charge transfer integrals obtained in this way differ significantly from values estimated from the energy splitting between the highest occupied molecular orbitals in a dimer. The difference is due to the nonzero spatial overlap between the molecular orbitals on adjacent molecules. Calculations were performed on unsubstituted and methoxy- or methylthio-substituted triphenylenes. Charge transfer integrals and site energies were computed as a function of the twist angle, stacking distance and lateral slide distance between adjacent molecules. The variation of the charge transfer integrals and site energies with these conformational degrees of freedom provide a qualitative explanation of the similarities and differences between the experimental charge carrier mobilities in different phases of alkoxy- and alkylthio-substituted triphenylenes. The data obtained from the present work can be used as input in quantitative studies of charge transport in columnar stacked triphenylene derivatives. (C) 2003 American Institute of Physics.