Thioflavin T Inspirations: On the Photophysical and Aggregation Properties of Fluorescent Difluoroborates Based on the Benzothiazole Core

In this work, we investigated a novel series of fluorescent dyes based on benzothiazole core substituted with a palette of donor groups that differ in size, shape, and character (alkyl vs aromatic). These dyes exhibit an intramolecular charge transfer state in their electronic structure. The photophysical properties of the newly synthesized dyes were studied with an eye toward aggregation effects in solvents and mixtures of solvents differing in polarity. Moreover, multiphoton absorption studies were performed to determine the potential of the dyes in two-photon microscopy. The results of spectroscopic measurements were supported by electronic structure calculations using coupled-cluster theory. Overall, the results provide an indication regarding the optimal substituents to achieve bright emission in various media and how these properties are related to aggregation effects.