Theoretically, 2 can function as an ESIPT fluorophore when an -OH group is installed at the 2' position to give 3 (Scheme 1). In methanol, 3 displays an enol emission at 450 nm (Fig. , blue trace). Alternatively, a red-shifted keto emission at 520 nm appears in the nonpolar solvent dichloromethane (Fig. , green trace). This red-shift in emission in nonpolar solvents is characteristic of the ESIPT process. A small positive solvatochromism can be observed in the enol emission wavelength between methanol and phosphate buffer-likely due to differences in the protic state of the carboxylic acid in 3 between these two solvents (Fig. , purple trace). (2) Analysis of the binding interaction of 2 and WT TTR in Fig. , reveals that the -OH group at the 2'-position in 3 would clash with the A108 residue. This steric clash would prevent binding, but also indicates the necessary mutation that needs to be made to WT TTR□ in order to allow binding of an ESIPT fluorophore based on 3. Therefore, we hypothesized that an A108G mutation would remove the steric imposition of the A108 side chain to create room for the -OH group in 3.