MOLECULAR RECOGNITION INDICATORS OF MODIFIED CYCLODEXTRINS USING TWISTED INTRAMOLECULAR CHARGE-TRANSFER FLUORESCENCE

Modified alpha, beta, and gamma-cyclodextrins that bear one p-(dimethylamino)benzoyl (DMAB) moiety (DMAB-alphaCyD, DMAB-betaCyD, and DMAB-gammaCyD, 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-betaCyD. The TICT fluorescence intensity increased for DMAB-alphaCyD and DMAB-gammaCyD, and decreased for DMAB-betaCyD when the hosts form inclusion complexes with guest molecules, and the variation of the TICT emission intensity was used as a sensitivity parameter. DMAB-alphaCyD was effective to detect chain compounds while DMAB-gammaCyD showed high sensitivities to bulky compounds including several steroids. Various guest compounds were detected by DMAB-betaCyD, The orders of the sensitivities of the hosts were parallel with those of the binding constants except for the case of DMAB-gammaCyD. The results demonstrate that these fluorescent CyDs are useful as fluorescent indicators of molecular recognition.