THEORETICAL-STUDIES OF THE MOLECULAR 2ND-ORDER HYPERPOLARIZABILITIES OF POLYCYCLIC AROMATICS

Semiempirical-FF calculations were performed for the second-order hype rpolarizabilities [gamma] of a series of polycyclic aromatics to exami ne the structure-optical-property-relationship. First, [gamma] of the unsubstituted PAHs were presented. For linear polyacenes, [gamma] 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-m embered rings increased. For nonlinear PAHs, the chain topology should be taken into consideration. An empirical formula was given to relate the computed [gamma] and linear polarizabilities [alpha]. [gamma] of mono- and di-substituted PAHs were then presented to examine the subst ituent effects on [gamma].