Theoretical studies on second hyperpolarizabilities for cation radical states of tetrathiafulvalene and tetrathiapentalene

The static longitudinal second hyperpolarizabilities (gamma) for cation radical states of symmetric alternant and condensed-ring conjugated systems involving sulfur atoms, i.e., tetrathiafulvalene (TTF) and tetrathiapentalene (TTP), are calculated by using a density functional (B3LYP) method with extended basis sets. The spatial contributions of electrons to the gamma are investigated by using the hyperpolarizability density analysis. These molecules are found to provide unique third-order optical non-linearity, i.e., negative gamma. We also discuss a possibility of multi-property aggregate systems combining the unique third-order optical non-linearity and high electrical conductivity. (C) 1999 Elsevier Science B.V. All rights reserved.