AN EXPERIMENTAL–THEORETICAL INSIGHT INTO SYNTHESIS AND OPTICAL PROPERTIES OF STRUCTURALLY TUNED Π-CONJUGATED SCHIFF BASES

Novel Schiff bases 3a, 3b, and 3c were synthesized, and their optical properties were investigated through experimental methods focusing on the determination of optical band gaps (Eg) derived from UV/Vis absorption spectra. These compounds are identified as N-(6-methylbenzo[d]thiazol-2-yl)-1-(pyren-1-yl)methanimine (3a), 1-(anthracen-9-yl)-N-(6-methylbenzo[d]thiazol-2-yl)methanimine (3b), and 1-(9H-fluoren-2-yl)-N-(6-methylbenzo[d]thiazol-2-yl)methanimine (3c). To reveal the key structural and optical characteristics of these molecules, theoretical calculations were performed using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) at the B3LYP/6–31G(d,p) level. Theoretical results were compared with experimental data to comprehensively evaluate molecular geometries, UV/Vis spectroscopic parameters, and frontier molecular orbital (FMO) energy levels. Nonlinear optical (NLO) properties were analyzed in relation to molecular structure, substitution patterns, conjugation length, and intramolecular charge transfer (ICT) characteristics. The calculated first-order hyperpolarizability (β) values for compounds 3a, 3b, and 3c in DMSO were found to be 4379.6, 7261.4, and 7434.4 a.u., respectively, approximately 110, 183, and 187 times higher than that of the standard reference compound urea. These findings indicate that the synthesized Schiff bases are promising candidates for future applications in photonics and optoelectronics.