EFFECT OF BETA-CYCLODEXTRIN ON THE EXCITED-STATE PROPERTIES OF 3-SUBSTITUTED INDOLE-DERIVATIVES

The effect of beta-cyclodextrin on the absorption and fluorescence spe ctra of 3-R-indoles (R = CH3 or (CH2)(n)-COOH with n = 1, 2 and 3) was studied. The inclusion in beta-cyclodextrin barely changed the UV spe ctra, while significant variations were produced in the emission spect ra, particularly regarding the fluorescence quantum yields. These chan ges, which are pH dependent, allow the determination of the associatio n equilibrium constants (k(Assoc)) under different sets of conditions. For the derivatives with R = (CH2)(n)COOH, the k(Assoc) at pH = 2 inc reased linearly with the number of CH2 groups. The changes in fluoresc ence quantum yield are higher for the neutral than for the ionized com pounds due to greater changes in the nonradiative rates of the neutral species when it is un-ionized.