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.