SYNTHESIS, CRYSTAL-STRUCTURE AND INDO CALCULATION OF THE MOLECULAR HYPERPOLARIZABILITY OF A HIGHLY POLARIZABLE MEROCYANINE DYE

A zwitterionic cyanine dye of formula HOCH2CH2(NC5H4)CHCH(C6H4)O (M-2) is reported with its crystal structure. Crystal data: monoclinic (P2( 1)), a = 15.038, b = 5.385, c = 17.301 Angstrom, beta = 111.68, Z = 2. The nonlinear optical properties are investigated through solvatochro mism and found to be very similar to those of a related cyanine dye (M -1) having an extremely high molecular hyperpolarizability (beta). IND O calculations performed on both crystal structures indicate small mod ifications in the electronic properties, but which result in a large m odification of the hyperpolarizability in the solid: beta(M-2) = 2.5 x beta(M-1). In addition, the hydroxyethyl substituent can be employed for engineering the chromophore into acentric environments. Therefore, increasing NLO responses may be expected at both the molecular and ma croscopic levels with such systems.