Cyclodextrins twisted intramolecular charge transfer

Kim YH, Cho DW, Yoon M, Kim D (1996) Observation of hydrogen-bonding effects on twisted intramolecular charge transfer of p-(N, N-diethylamino) benzoic acid in aqueous cyclodextrin solutions. J Phys Chem 100(39) 15670-15676... 

K. Hamasaki, H. Ikeda, A. Nakamura, A. Ueno, F. Toda, I. Suzuki, andT. Osa, Fluorescence sensors of molecular recognition. Modified cyclodextrins capable of exhibiting guest-responsive twisted intramolecular charge transfer fluorescence, /. Am. Chem. Soc. 775,5035-5040(1993). 

However, in the presence of a guest molecule (cyclic alcohols, monoterpenes, steroids) binding to the cyclodextrin cavity, the twisted intramolecular charge-transfer (TICT) emission of the host decreases significantly, indicating the process schematically shown in Figure 2. 

Figure 2 DMAB-/ -cyclodextrin for the detection of guest binding by twisted intramolecular charge-transfer (TICT) fluorescence [7,8]...

Since the dynamics of the twisted intramolecular charge transfer (TICT) process is very sensitive to the polarity of the medium, the local polarity of an organized medium may also be determined from the rate of the HCT process. For TNS, which is nearly nonfluorescent in water ((j)f = 10 and Xf = 60 ps), the emission quantum yield and lifetime increases nearly 50 times on binding to cyclodextrins and more than 500 times on binding to a neutral micelle, TX -100 [86]. Such a dramatic increase in the emission intensity and lifetime arises because of the marked reduction of the nonradiative HCT process inside the less polar microenvironment of the cyclodextrins and the micelle. Determination of the micropolarities of various organized assemblies using TICT probes has been surveyed quite extensively in several recent reviews [5b-d,f,86]. Therefore, in this chapter we will focus only on some selected works not covered in the earlier reviews. 

Nag, A. and Bhattacharyya, K., Twisted intramolecular charge-transfer emission of dimethylami-nobenzonitrile in a-cyclodextrin cavities, Chem. Phys. Lett., 151, 474,1998. 

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