Effect of Solvent on Donor and Acceptor Schiff Base of (E)-5-(diethylamino)-2-(4-nitrophenyl)methyl Phenol: Photophysical, Theoretical, Molecular Docking Studies, and Biological Applications

The photophysical properties of the donor N,N-diethylamino (-NEt₂) and acceptor nitro (-NO₂) group substituted salicylideneaniline derivative (E)-5-(diethylamino)-2-(4-nitrophenyl)methylphenol (DSAN), were investigated using steady-state and time-resolved fluorescence spectroscopy. Different solvents showed intramolecular charge transfer (ICT) and excited-state intramolecular proton transfer (ESIPT) states. The pH effect on DSAN revealed enol, ICT, ESIPT states, and anionic forms. Solute–solvent interactions, like hydrogen bonding, influenced longer wavelength emissions in high-polarity solvents, indicating the ICT state. DFT studies optimized the DSAN molecule in various solvents, and electrostatic potential analysis identified electrophilic and nucleophilic areas and the HOMO–LUMO band energy gap was around 3.0 eV. Also the molecular docking studies showed DSAN's hydrophobic and hydrogen bond interactions with thymidylate synthase (TS). Biological studies indicated DSAN has minimal antioxidant and antimicrobial activity.