Lophine-benzazole molecular hybrids with dual emission and large Stokes shifts: Experimental and theoretical insights into ESIPT dynamics

Abstract

Lophine-benzazole molecular hybrids were synthesized through an efficient tetracomponent condensation reaction involving benzil, benzaldehyde, ammonium acetate, and aminobenzazoles. The resulting compounds were characterized by NMR, FTIR, melting point analysis, and X-ray crystallography. The structural framework combines two distinct classes of fluorophores, lophines and ESIPT-active benzazoles, yielding dyads with dual emission characteristics. Photophysical studies revealed that the hybrids exhibit excitation-dependent fluorescence and very large Stokes shifts, attributed to excited-state intramolecular proton transfer (ESIPT) processes. The presence of intramolecular hydrogen bonds and the influence of the local environment on emission behavior were confirmed through steady-state and time-resolved fluorescence spectroscopy, supported by calculations using the Density Functional Theory (DFT) and time-dependent DFT (TD-DFT), employing the ωB97X-D3/def2-TZVP methodology. The combined experimental and theoretical insights underscore the potential of these conjugated systems as responsive luminescent materials for optoelectronic and sensing applications.