<p>Organic solar cells (OSCs) require low-cost, solution-processable materials with tunable optical properties to enhance light-harvesting efficiency. Schiff bases, a class of <i>π</i>-conjugated small molecules containing the imine (C=N) linkage, offer structural versatility that enables direct control over their HOMO/LUMO levels and charge-transfer behavior. In this study, a new Schiff base, SH3, was synthesized via the condensation of benzidine with vanillin at a 90% yield and structurally confirmed by FTIR, ¹H-NMR and ¹³C-NMR analyses. Thin films of SH3 were prepared from three solvents—dichloromethane (DCM), methanol (MOH), and dimethylformamide (DMF)—spin-coated and annealed at 50°C, 100°C and 150°C to investigate the influence of processing conditions on their optical characteristics. Annealing markedly altered the absorption profiles of the SH3 thin films, inducing a distinct visible peak near 680 nm. The optimal optical performance was obtained for SH3/DCM films annealed at 100 °C, while SH3/MOH and SH3/DMF films showed maximum absorption at 50 °C. UV-Vis spectroscopy revealed a strong <i>π</i> → <i>π</i>* absorption band at 359 nm with a high molar absorptivity (<i>ε</i> = 67,992 M⁻¹&#xa0;cm⁻¹), an emission maximum at 532 nm and a large Stokes shift (8752 cm⁻¹), indicating substantial excited-state reorganization. Electrochemical studies showed an oxidation onset (<i>E</i>_ox) of 1.31 V, corresponding to HOMO and LUMO levels of − 5.71 eV and − 2.74 eV, respectively, yielding an energy gap of 2.9 eV. These results demonstrate that both solvent and annealing temperature significantly influence the optical absorption and energy-level alignment of SH3. The favorable electronic configuration and strong visible absorption of annealed SH3/DCM films suggest their potential as efficient donors or interfacial materials for enhancing light harvesting and photoelectric conversion efficiency in organic solar cells.</p>