Electronic and vibrational polarizability and first hyperpolarizability of charge transfer chromophores: Quantum chemistry investigation

Abstract

Static vibrational and electronic contributions to the longitudinal polarizability (α) and first hyperpolarizability (β) have been calculated, within the double harmonic oscillator approximation, at the HF/6-31G for a set of polyconjugated, D-linker-A, compounds. Effects due to the nature of the linker and of the D/A-pair type, on the geometrical structures and the electrical properties, are investigated. It turns out that, for a given linker, in almost all cases, the static ${\mathit{\beta }}_{\mathit{L}}^{\mathit{e}}$ (0) and ${\mathit{\beta }}_{\mathit{L}}^{\mathit{v}}$ (0) vary in the same order, with the type of the acceptor group A (A # NO₂, COH, CF₃). As well, the pair HO/NO₂ was associated the greatest ${\mathit{\beta }}_{\mathit{L}}^{\mathit{e}}\mathrm{(}0\mathrm{)}$ and ${\mathit{\beta }}_{\mathit{L}}^{\mathit{v}}\mathrm{(}0\mathrm{)}$ values. The analysis upon the SOM expressions, due to Bishop and Kirtman, demonstrates that, more than 50% of ${\mathit{\beta }}_{\mathit{L}}^{\mathit{v}}$ owes to three, two or even to only one vibrational normal mode contribution. Moreover, the vibrational modes with frequencies at, or more than, 3000 cm⁻¹ present a null individual vibrational first hyperpolarizability.