Theoretical studies of the molecular second-order hyperpolarizabilities of polycyclic aromatics

Abstract

Semiempirical-FF calculations were performed for the second-order hyperpolarizabilities 〈γ〉 of a series of polycyclic aromatics to examine the structure–optical–propertyrelationship. First, 〈γ〉 of the unsubstituted PAHs were presented. For linear polyacenes, 〈γ〉 and total resonance energy were found to be increased while the HOMO-LUMO gap and resonance energy per electron decreased as the number of six-membered rings increased. For nonlinear PAHs, the chain topology should be taken into consideration. An empirical formula was given to relate the computed 〈γ〉 and linear polarizabilities 〈α〉. 〈γ〉 of mono- and di-substituted PAHs were then presented to examine the substituent effects on 〈γ〉. © 1995 John Wiley & Sons, Inc.