Inclusion complexes of some 3H-indoles with cyclodextrins studied through excited state dynamics and steady state absorption and fluorescence spectroscopy

We present a steady state and time-resolved fluorescence study of two 3H-indole molecules, namely 2-[(p-amino)phenyl]-3,3-dimethyl-5-cyano-3H-indole (1) and 2-[(p-dimethylamino)phenyl]-3,3-dimethyl-5-cyano-3Hindole (2) in aqueous solutions of alpha-,beta- and gamma-cyclodextrins. The stoichiometries and association constants of the molecules have been assessed in the different cyclodextrin (CD) systems. The spectral characteristics, bandwidths and association constants show that molecule 2 experiences a stronger interaction with the host CDs than molecule 1. Steady state fluorescence experiments show the presence of only one kind of complex for the molecules in alpha- and gamma-CDs, whereas time-resolved fluorescence measurements and global analysis reveal the presence of two kinds of complex, thereby demonstrating the higher sensitivity of the time-resolved experiments. Fluorescence quenching is observed for both molecules in gamma-CD, whereas in alpha- and beta-CDs fluorescence enhancement is found. This has been correlated with the lower quantum yield of the complex in the former case. The observations of fluorescence quenching, together with the magnitudes of the association constants, show that the molecules form different complexes with gamma-CD compared with alpha- and beta-CDs.