Design, synthesis and photophysical properties of novel 2,4-disubstituted quinazolines

A series of 2,4-diarylquinazolines bearing a 4-(trifluoromethyl)phenyl, 4-cyanophenyl, or 4-(formyl)phenyl group at position 4 and an electron-donating substituent at position 2 were synthesized via Pd-catalyzed cross-coupling of 4-bromo derivatives with arylboronic acids. A counterpart with a cyano group directly attached to the quinazoline core was also prepared. The UV–Vis absorption and photoluminescence properties of dilute solutions of these compounds were investigated, revealing that 2-(3,4-dimethoxyphenyl)quinazolines and 2-(9-ethyl-9H-carbazol-3-yl)quinazolines exhibited emission in toluene with quantum yields of up to 26 %. Furthermore, 9-ethyl-9H-carbazol-3-yl-substituted derivatives demonstrated emission in the solid state with efficiencies up to 15 %. The absorption and emission behavior in solvents with different polarities were examined for selected fluorophores, and their solvatochromism was assessed using the Lippert-Mataga, Bakhshiev, and Ravi equations. While the absorption spectra were solvent-independent, the emission spectra were significantly dependent on solvent polarity, confirming the formation of ICT states. Electrochemical studies and DFT calculations were performed to support the experimental observations. Notably, the synthesized formyl derivatives hold promise for use in the development of materials for dye-sensitized solar cells through condensation reactions with active methylene compounds.