Fluorescent Sensors of Molecular Recognition. Modified Cyclodextrins Capable of Exhibiting Guest-Responsive Twisted Intramolecular Charge Transfer Fluorescence

α-, β-, and γ-cyclodextrin derivatives bearing a p-(dimethylamino)benzoyl (DMAB) moiety (DMAB-αCyD, DMAB-βCyD, and DMAB-γCyD, respectively) have been synthesized as fluorescent sensors of molecular recognition. These compounds show dual fluorescence emission arising from normal planar (NP) and twisted intramolecular charge transfer (TICT) exited states, and among them strong TICT emission was observed for DMAB-βCyD. The induced circular dichroism spectra of the derivatives suggest that only DMAB-βCyD among other derivatives binds the DMAB moiety into its own cavity, forming an intramolecular inclusion complex. This conformation was confirmed by the analysis of its ¹H-NMR data and was related to its strong TICT emission. The intensity of the TICT emission of DMAB-βCyD decreased markedly with increasing the concentration of cyclic alchols, monoterpenes, or steroids. This observation was explained by the guest-induced location change of the DMAB moiety from inside to outside of the cavity. Since the TICT emission intensity depended on the size, shape, and polarity of the guest molecules, DMAB-βCyD was useful as a fluorescent chemosensor of molecular recognition.