The absolute proton affinity and the second order hyperpolarizability of some catacondensed linear polyacenes and pericondensed zethrenes

Abstract

Simple relationships between the absolute proton affinities APAs and second order hyperpolarizabilities γ is found for a class of condensed aromatic molecules with the conjugated π-electron network. Results are presented for “open” acenes and zethrenes in comparison with “closed” systems (coronene and kekulene). They indicate a strong dependence of the APA–γ relation on the molecular shape. Since γ is intimately related to a nonlinear response of the system, it follows that APA could serve as a useful probe for testing the nonlinear polarizability at the molecular level, thus selecting possible candidates for materials with nonlinear optical (NLO) properties. It also appears that zethrenes represent very useful building blocks for NLO materials. An interesting byproduct of this study is that zethrenes could be strongly basic compounds, if appended by a judicious selection of the electron releasing substituents placed at the strategic positions on the molecular perimeter.