Experimental and theoretical study of three newly-synthesized iminochalcones: An example of dual emission induced by polarity changes

Abstract

A series of iminochalcones derived from 3-(4-aminophenyl)-1-(4-hydroxyphenyl)prop-2-en-1-one, were synthesized using different p-substituted benzaldehydes (R = –N(CH3)2 (2a), –H (2b) and –NO2 (2c)). The melting points of these compounds depend on the substituent (2c > 2a > 2b) as a function of the intermolecular interactions. The absorption spectra of the iminochalcones present two bands and are very sensitive to solvent polarity due to the ICT character of the π → π* transition on the cinnamoyl group. The relative intensity between the two main absorption bands of 2c is induced by solvent polarity and depends on the character of the orbitals. Excitation and fluorescence experiments showed that iminochalcone 2a presents dual fluorescence. Together with DFT calculations, these results corroborate the polarity-induced change model in the energy order of the emissive states, indicating that both emission bands are derived from LE and ICT excited states.