Synthesis and Characterization of Fluorescent Molecular Rotors

Small molecule fluorescent probes provide a non-invasive way to obtain accurate microviscosity measurements for biological analyses, especially when bulk measurements are not feasible. A family of push-pull fluorescent dyes, inspired by the benzothiazole motif of Thioflavin T, are reported, along with preliminary data on their use for visualizing long-range bacterial signaling and binding affinities for amyloids. By altering the ?-wire through increased conjugation and heteroatom substitution, a red-shifted ThT analogue was successfully synthesized. Synthetic analogues of previously reported fluorescent probes were also synthesized. Increasing the ?-wire from phenyl to naphthyl induced a bathochromic shift. It was also observed that switching from an ester to an amide altered photophysical properties in both sets of analogues. There was a slight hypsochromic shift due to the amide, likely attributed to the slight decrease in electron-withdrawing character of the acceptor group. Moreover, the emission intensity of the FRET donor decreased in the amide ratiometric system as compared to that of its ester counterpart, potentially indicating an enhancement of energy transfer between the donor and acceptor pair. These studies point towards ways to optimize the chemical structures of various fluorescent probes for specific applications