A TD‐DFT/DFT study on the ESIPT and photophysical properties of symmetrical 2‐hydroxybenzilidene1,3‐diamines derivatives

Abstract

AbstractDensity functional theory (DFT) and Time dependent density functional theory (TD‐DFT) methods are used to simulate the photoexcitation and emission of the symmetrical 2‐hydroxybenzilidene1,3‐diamine (HBDA) Schiff base and some of its derivatives in the gas phase and solution. Our aim here is to explore the details of Excited‐State Intramolecular Proton Transfer (ESIPT) which underlies the activity of HBDA molecules as fluorescent probes. The structures of HBDA in S0 and the S1 states are optimized utilizing the DFT and TD‐DFT methods, respectively. Geometric configurations, electronic spectra, frontier molecular orbitals, and potential energy surfaces have all been computed and analyzed for the purpose of interpreting the mechanism of ESIPT. The geometries and relative stabilities of 15 tautomeric forms and the corresponding isomers of the studied molecules have been identified and their relative stabilities are investigated. The potential energy profiles and intrinsic reaction coordinates (IRC) calculations along the proton transfer coordinates both in the ground and in the excited state are monitored as well. The impact of the donating (OMe) and withdrawing (NO2) groups on the single and double proton transfers are investigated both in the gas phase and solution.