Influence of cyclodextrins on the fluorescence of some short and long chain linked flexible bisbenzenes in aqueous solution

The UV absorption, induced circular dichroism (icd) spectra, steady state and time resolved fluorescence emission of the flexible bisbenzenes 1-4 were obtained in aqueous solution and in presence of alpha-, beta-, and gamma-cyclodextrin (CD). Bisbenzenes 1 and 2 in an aqueous environment exhibit a dual emission which is differently affected by the CDs. The long-wavelength emission is quenched by alpha- and beta-CD and enhanced by gamma-CD. This is due to the formation of inclusion complexes between the CDs and 1 (2) in the ground state, in agreement with the modifications of the UV spectrum and the appearance of icd signals. On the basis of these effects and of the influence of the CDs on the 1 and 2 lifetimes, the dual emission of these bisbenzenes is attributed to a set of different ground-state conformations.