UNDERSTANDING THE ROLE OF WATER IN PROMOTING E-ISOMER PRODUCTION AND PHOTOCHROMISM OF SOLID SCHIFF BASE: A DFT AND TD-DFT STUDY

The formation mechanism and photochromic property of a novel solid state Schiff base compound (E-isomer, C 21 H 18 I 2 N 3 O 2) derived from 4-aminoantipyrine and 3,5-diiodosalicylaldehyde is investigated in this work using density functional theory at the B3LYP/6-31l++G** level with and without solvent water presence. Our computational results show that the conversion in the gas phase is unlikely to occur and the solvent water is involved in the reaction to decrease the barrier height. We considered one to three water molecule participations in the water-catalyzed mechanism to produce the E-isomer. Time-dependent density functional theory (B3LYP/6-311+G*) is employed to examine the photochromic property of the molecule. A large Stokes shift between absorption and emission has been attributed to the intramolecular H-transfer ( O – H ⋯ N to O ⋯ H – N ) following photoexcitation of the enol species, suggesting that the keto form of the photoproduct structure plays the key role, in agreement with the experimental finding of stereoselectivity. Conceptual DFT reactivity indices are employed to rationalize the findings from the present study.