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–coumar...