The nonlinear optical (NLO) properties of carbazole–coumarin-based chalcones and their OBO complexes of D−π–A and D−π–A−π–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 (α), hyperpolarizability (β), and second-order hyperpolarizability (γ) 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 ζ 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 (χ(3)) of the dyes. The structure–property relationship has been well established in the studied dyes, which can act as better organic NLOphores.

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To investigate the effect of substituents in azo dyes on their nonlinear optical properties, four azo dyes were synthesized using ethyl‐3‐hydroxy‐2‐naphthoate as a coupler and characterized. The polarizability (α) and hyperpolarizability (β and γ) constants were determined by using solvatochromic and computational method. A group of global hybrid and range seperated hybrid functionals having different Hartree‐Fock exchange percentage were used to evaluate the NLO properties. The functional ωB97 and ωB97XD performed better in the determination of polarizability (α) and hyperpolarizability (β and γ), respectively. The observed results for polarizability and hyperpolarizability parameters were supported by highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) energy gap, Hammett‐coefficient (σ), excited‐state coefficients (σex), and hyper‐hardness (Γ) values. Third‐order NLO properties were analyzed by using Z‐scan technique. The –OCH3 substituted dye 4d shows higher value of molecular susceptibility (χ(3)), polarizability (α), and hyperpolarizability (β and γ) parameters among the studied azo dyes. They are likely to have the potential applications in optoelectronics and photonics.

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