CHROMOPHORE ENVIRONMENTAL-EFFECTS IN SALTLIKE NONLINEAR-OPTICAL MATERIALS - A COMPUTATIONAL STUDY OF ARCHITECTURE ANION 2ND-ORDER RESPONSE RELATIONSHIPS IN HIGH-BETA STILBAZOLIUM SELF-ASSEMBLED FILMS

The very large cation-anion environmental effects on second-order nonl inear optical response observed in self-assembled stilbazolium monolay er ion-exchange experiments are investigated theoretically using the Z INDO/SOS quantum chemical formalism. Ion pairs consisting of the 4'-(d imethylamino)-N-methyl-4-stilbazolium cation with chloride, iodide, an d p-aminobenzenesulfonate counteranions in differing mutual orientatio ns, are examined as models to relate calculated ion pair hyperpolariza bilities to anion-exchange-induced changes in macroscopic linear optic al and nonlinear optical response. Calculated hyperpolarizabilities de pend strongly on the relative cation-anion packing configuration. In a ccord with anion exchange experiments, enhancements of the second-orde r nonlinear optical response on passing from Cl- to I- and p-aminobenz enesulfonate can be related to likely displacement of the bulkier I- a nd p-aminobenzenesulfonate anions from more closely packed structural arrangements originally produced as a consequence of the self-assembly process.