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

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2022-04, Vol.426, p.113725, Article 113725
• Main Authors: Riga-Rocha, Beatriz A., Machado, Antonio E.H., Neumann, Miguel G., Cavalheiro, Carla C.S.
• Format: Article
• Language: English
• Subjects: Chalcones; Dual fluorescence; Iminochalcones; Substituent effect
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2021.113725

[Display omitted] •Iminochalcones with different substituents were synthesized and characterized.•Spectral properties of these compounds are highly sensitive to solvent polarity.•Dual fluorescence due to change in polarity is found for one of the compounds.•DFT calculations confirm the energies of the LE and ICT polar emissive states. 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.