Molecular Recognition Indicators of Modified Cyclodextrins Using Twisted Intramolecular Charge Transfer Fluorescence

Modified α, β, and γ-cyclodextrins that bear one p-(dimethylamino)benzoyl (DMAB) moiety (DMAB-αCyD, DMAB-βCyD, and DMAB-γCyD, respectively) were synthesized as fluometric molecular recognition indicators. These three modified cyclodextrins show dual fluorescence arising from normal planar and twisted intramolecular charge transfer (TICT) excited states. Among them, the TICT emission was particularly great in the case of DMAB-βCyD. The TICT fluorescence intensity increased for DMAB-αCyD and DMAB-γCyD, and decreased for DMAB-βCyD when the hosts form inclusion complexes with guest molecules, and the variation of the TICT emission intensity was used as a sensitivity parameter. DMAB-αCyD was effective to detect chain compounds while DMAB-γCyD showed high sensitivities to bulky compounds including several steroids. Various guest compounds were detected by DMAB-βCyD, The orders of the sensitivities of the hosts were parallel with those of the binding constants except for the case of DMAB-γCyD. The results demonstrate that these fluorescent CyDs are useful as fluorescent indicators of molecular recognition.