Synthesis and Photophysical Studies of a Series of Quinazoline Chromophores

The synthesis of a series of push-pull arylvinyl (styryl), aryl, and arylethynyl quinazoline derivatives by means of different straightforward protocols is reported. The photophysical properties of the compounds are described. The preparation of arylvinylquinazolines was performed by aldol condensation of the appropriate methylquinazoline and functionalized benzaldehyde. Suzuki and Sonogashira cross-coupling reactions were used to prepare the aryl and arylethynyl compounds, respectively, starting from chloroquinazolines. Optical studies revealed that all of the compounds reported here behave in a way similar to that of their pyrimidine counterparts, with absorption bands in the UV or visible region and the emission of green light upon irradiation. Large red shifts were observed in the fluorescence emission maxima upon increasing the solvent polarity. This strong emission solvatochromism suggests the formation of an intramolecular charge-separated emitting state. The materials can be easily and reversibly protonated at the nitrogen atoms of the heterocyclic ring, and this causes dramatic color changes. This phenomenon opens up the possibility of developing colorimetric pH sensors that can be efficiently modified a posteriori for specific applications.