1-H-indol-2,3-dione-based schiff base derivatives: Synthesis, optoelectronic properties, and DFT-theoretical insights for photovoltaic applications

Abstract

Two novel 1-H-indol-2,3-dione–based Schiff base derivatives, MIT and DIT, were synthesized via condensation of indolinone with selected aldehydes. UV–Vis spectra in various solvents showed two absorption bands: π→π∗ (300–320 nm) and n→π∗ (400–500 nm), with maxima at 307 nm for MIT (toluene) and 321 nm for DIT (acetonitrile). Steady-state fluorescence exhibited emission peaks at 497 nm for MIT (CHCl₃) and 443 nm for DIT (MeCN). Cyclic voltammetry revealed oxidation onset potentials of 1.43 V (MIT) and 1.10 V (DIT) vs. Fc/Fc⁺, corresponding to HOMO energies of −6.09 eV and −5.66 eV, and electrochemical gaps of 2.31 and 2.25 eV. Ground-state geometry optimizations were performed at the B3LYP/6-31+G(d,p) level, and TD-DFT calculations employing B3LYP, CAM-B3LYP, and ωB97X-D functionals with the 6–311++G(d,p) basis set and IEFPCM solvent effects demonstrated consistency with the experimental trends. NBO and ESP analyses indicated nucleophilic carbonyl oxygens (−0.587 to −0.643) and electrophilic imine nitrogens (∼−0.47). Frontier molecular orbital analysis showed delocalized HOMO→LUMO transitions with strong π–π∗ and intramolecular charge-transfer character. Theoretical λ_max values (≈290–340, 375–540 nm) matched experiments, with a bathochromic shift for DIT (∼537–539 nm). Photovoltaic parameters including light harvesting efficiency (LHE), excited-state oxidation potential (E^dye∗), injection driving force (ΔG_inj), regeneration energy (ΔG_reg), open-circuit voltage (V_OC), fill factor (FF), and power conversion efficiency (η) were calculated. DIT displayed higher LHE, while MIT exhibited slightly higher η due to its greater V_OC. These results highlight the potential of indol-2,3-dione Schiff bases for optoelectronic and photovoltaic applications.