Synthesis, crystal structure and INDO calculation of the molecular hyperpolarizability of a highly polarizable merocyanine dye
Abstract
A zwitterionic cyanine dye of formula HOCH2CH2(NC5H4)CHCH(C6H4)O (M2) is reported with its crystal structure. Crystal data: monoclinic (P21), a=15.038, b=5.385, c=17.301 Å, β=111.68, Z=2. The nonlinear optical properties are investigated through solvatochromism and found to be very similar to those of a related cyanine dye (M1) having an extremely high molecular hyperpolarizability (β). INDO calculations performed on both crystal structures indicate small modifications in the electronic properties, but which result in a large modification of the hyperpolarizability in the solid: β(M2)=2.5×β(M1). 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 macroscopic levels with such systems.