Enhancement of NLO Properties in OBO Fluorophores Derived from Carbazole-Coumarin Chalcones Containing Carboxylic Acid at the N-Alykl Terminal End

The nonlinear optical (NLO) properties of carbazole-coumarin-based chalcones and their OBO complexes of D-pi-A and D-pi-A-pi-D types with carbazole as donor substituted with N-alykl chain at the 9 position with carboxylic acid end group are studied in detail. These dyes exhibit good emission solvatochromism. The NLO properties of dyes 5-8 were studied by two methods, namely, solvatochromic and computational method. The linear polarizability (alpha), hyperpolarizability (beta), and second-order hyperpolarizability (gamma) of dyes 5-8 were studied by time-dependent density-functional theory computational method using five different range-separated functionals, namely, CAM-B3LYP, HISSbPBE, HSEH1PBE, wB97, and wB97X, with triple zeta basis set 6-311++G(d,p). The correlation between the NLO properties is well established with the geometry of the dyes by understanding the enhancement of hyperpolarizability, second-order hyperpolarizability, and two-photon absorption (TPA) properties of complexed and uncomplexed carbazole-coumarin chalcones experimentally and theoretically. The dye 8 showed maximum enhancement in the NLO properties like 167 GM two-photon absorption cross section in toluene, which is due to the effective charge transfer in the molecule owing to the presence of extra donor and rigidized planar conformation of the dye due to OBO complexation of the chalcone. Z-scan technique was used to study the third-order nonlinearity (chi((3))) of the dyes. The structure-property relationship has been well established in the studied dyes, which can act as better organic NLOphores.