SPECTRAL AND PHOTOPHYSICAL STUDIES OF INCLUSION COMPLEXES OF SOME NEUTRAL 3H-INDOLES AND THEIR CATIONS AND ANIONS WITH BETA-CYCLODEXTRIN

Interactions between 3H-indole derivatives, their cations and anions, and microheterogeneous environments like micelles and vesicles have be en studied extensively in our laboratory recently. We report herein th e interactions of 2-(p-aminophenyl)-3,3-dimethyl-5-cyano-3H-indole (1) and methylamino)phenyl]-3,3-dimethyl-5-cyano-3H-indole (2) with aqueo us solutions of beta-cyclodextrin (beta B-CD), studied by absorption a nd fluorescence steady-state and time-resolved measurements. The stoic hiometries of the cyclodextrin:guest inclusion complexes have been det ermined by steady-state fluorescence measurements. The data reveal tha t two types of complexes, i.e., 1:1 and 2:1 types are formed. Thermody namic parameters are calculated at six different temperatures. Spectra l characteristics, bandwidths, and photophysical parameters indicate t hat molecule 2 is better protected against hydrophilic interactions. P rotonation reactions carried out at different concentrations of beta-C D show that the protonation is inhibited at the indolic nitrogen, cont rary to what was observed in other microheterogeneous media. Time-reso lved measurements and global analysis of the results are best describe d by a discrete triple exponential decay law clearly indicating that t he guest molecules experience three different environments in aqueous solutions: bulk water and a stepwise 1:1 and 2:1 (beta-cyclodextrin:gu est) inclusion complexation. The effective polarity of the cyclodextri n cavity is equivalent with the polarity of an 80:20 methanol-water mi xture at the beta-CD rim where the indolic (tertiary) nitrogen is like ly to be located near the ''alcoholic'' secondary rim of the macrocycl e.