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

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: pi ->pi & lowast; (300-320 nm) and n ->pi & lowast; (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 omega B97X-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 (similar to-0.47). Frontier molecular orbital analysis showed delocalized HOMO -> LUMO transitions with strong pi-pi & lowast; and intramolecular charge-transfer character. Theoretical lambda(max) values (approximate to 290-340, 375-540 nm) matched experiments, with a bathochromic shift for DIT (similar to 537-539 nm). Photovoltaic parameters including light harvesting efficiency (LHE), excited-state oxidation potential (E-dye & lowast;), injection driving force (Delta G(inj)), regeneration energy (Delta G(reg)), open-circuit voltage (V-OC), fill factor (FF), and power conversion efficiency (eta) were calculated. DIT displayed higher LHE, while MIT exhibited slightly higher eta due to its greater V-OC. These results highlight the potential of indol-2,3-dione Schiff bases for optoelectronic and photovoltaic applications.