Excited-state charge coupled proton transfer reaction via the dipolar functionality of salicylideneaniline

Based on design and synthesis of salicylideneaniline derivatives (1a–1d), we demonstrate a prototypical system to investigate the excited-state intramolecular charge transfer (ESICT) coupled excited-state intramolecular proton transfer (ESIPT) reaction via the dipolar functionality of the molecular framework. In solid and aprotic solvents 1a–1d exist mainly as E conformers that possess an intramolecular six-membered-ring hydrogen bond. Compounds 1a–1c exhibit a unique proton-transfer tautomer emission, while compound 1d exhibits remarkable dual emission due to the different solvent-polarity environment between ESICT and ESIPT states. Time-dependent density functional theory (TDDFT) calculations are reported on these Schiff bases in order to rationalize their electronic structure and absorption spectra.

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