STRONG ENHANCEMENT OF NONLINEAR-OPTICAL PROPERTIES THROUGH SUPRAMOLECULAR CHIRALITY

A new approach to second-order nonlinear optical (NLO) materials is re ported, in which chirality and supramolecular organization play key ro les. Langmuir-Blodgett films of a chiral helicene are composed of supr amolecular arrays of the molecules. The chiral supramolecular organiza tion makes the second-order NLO susceptibility about 30 times larger f or the nonracemic material than for the racemic material with the same chemical structure. The susceptibility of the nonracemic films is a r espectable 50 picometers per volt, even though the helicene structure lacks features commonly associated with high nonlinearity. Susceptibil ity components that are allowed only by chirality dominate the second- order NLO response.