Photophysics and excited-state proton transfer of 2′-hydroxy-2-trans-styrylquinoline

2-StQ-2OH possessing a proton donor group (hydroxy) and a proton acceptor group (quinoline) was synthesized in order to study the influence of structural effects on the excited-state proton transfer (ESPT) and tautomerization. PT were observed for ground-state hydrogen-bonding complex between 2-StQ-2OH and 2,2,2-trifluoroethanol (TFE) or with triethylamine. In aqueous solution, ESPT can only be observed in α-cyclodextrin (α-CD) inclusion complex. The dielectric constant values of the α-CD cavities probed by 2-StQ-2OH and 2-StQ-2OMe are 8.5 and 6.3, respectively, because of the difference in size of the probe molecule inside the cavity.