Synthesis, photophysical properties and two-photon absorption of benzothiazole/benzoxazole π-expanded carbazole dyes

We report the synthesis and spectroscopic characterization (NMR, HRMS) of a series of benzazole derivatives with different carbazole substituents. The photophysical properties of these molecules were investigated in several solvents of different polarity by UV–vis absorption and fluorescence spectroscopy. These dyes show strong absorption bands in the near ultraviolet region, fluorescence emission with high quantum yields in the blue-green as well as large Stokes' shifts. Two-photon absorption properties were recorded and all of the dyes show moderate TPA cross sections in the 700–800 nm zone. Molecular modeling was also used to explain spectroscopic behavior of these dyes. Interestingly, they possess high thermal stability.