10.1021/acsomega.8b02761.s001 Reem H. Alzard Reem H. Alzard Muna S. Bufaroosha Muna S. Bufaroosha Noura Al-Shamsi Noura Al-Shamsi Amir Sohail Amir Sohail Naji Al-Dubaili Naji Al-Dubaili Alaa A. Salem Alaa A. Salem Ibrahim M. Abdou Ibrahim M. Abdou Na’il Saleh Na’il Saleh Solubilization of Pyridone-Based Fluorescent Tag by Complexation in Cucurbit[7]uril American Chemical Society 2019 UV enol form Time-resolved fluorescence results CB 7 host time-resolved fluorescence spectra keto form CB 7 complexes TFP 2019-01-10 19:36:07 Journal contribution https://acs.figshare.com/articles/journal_contribution/Solubilization_of_Pyridone-Based_Fluorescent_Tag_by_Complexation_in_Cucurbit_7_uril/7575338 Aimed at further exploring the hosting properties of cucurbit[7]­uril (CB7), we have exploited the spectroscopic and photophysical properties of a known fluorescent label as the guest molecule, namely, 3-cyano-6-(2-thienyl)-4-trifluoromethyl pyridine (TFP), in neat solvents. The formation of an inclusion host–guest complex with CB7 was checked by UV–vis absorption spectroscopy, and the value of binding constant (9.7 × 10<sup>5</sup> M<sup>–1</sup>) was extracted from the spectrophotometric data. The modulation of keto–enol equilibrium in TFP by the local environment is governed by the interplay between dimerization through intermolecular hydrogen bonding between individual solute molecules, favoring the enol form, and intermolecular hydrogen bonding between TFP and the surrounding solvents, favoring the keto form. Time-resolved fluorescence results established that the macromolecular CB7 host stabilizes preferentially the neutral enol form over the keto form of TFP. Unprecedentedly, our results reveal a linear dependence of the amplitudes of the extracted decay-associated spectra from the time-resolved fluorescence spectra of TFP on the sum of polarity/polarizability and hydrogen bonding parameters of the local environment, confirming that TFP at micromolar concentration in the CB7 complexes is experiencing a methanol-like environment. The results rationalized the 42-fold enhancement in the solubility of TFP in water media by complexation in CB7.