Ground and excited-state properties of 1,3-benzoselenazole derivatives: A combined theoretical and experimental photophysical investigation

A series of 1,3-benzoselenazole derivatives were prepared with different substituents by complementary methodologies starting from aldehydes or carboxylic acids, using sodium metabisulfite and tributylphosphine, respectively, according to the substituent pattern. The photophysical behaviour in solution of the benzoselenazoles was studied using UV–Vis absorption and steady-state fluorescence emission spectroscopies. These compounds present absorption maxima located in the UV region due to spin and symmetry, which allowed electronic transitions 1ππ*. The absorption maxima location, as well as the evidence of intramolecular charge transfer (ICT), was shown to be tailored by the position and electronic character of the substituents. Quantum chemical calculations using DFT and TDDFT were performed in order to investigate the electronic and photophysical features of the molecules. The calculations confirmed the presence of ICT in the molecules which contained nitro group in their structure and in all compounds where the allowed electronic transitions 1ππ* were taking place. In addition, the compounds showed significantly different fluorescence emissions depending on the solvent and their chemical structures, where structured and non-structured spectra in the range of 300–600 nm, with ICT character, were obtained.