Observation of alpha-terthiophene excited dimer fluorescence in aqueous solutions of gamma-cyclodextrin

The photophysical properties of inclusion complexes formed with gamma-cyclodextrin (gamma-CD) as host and 2,2':5',2 ''-terthiophene (alpha T) as guest have been investigated. The host:guest complexes formed at constant alpha T concentration are 1:1 at low gamma-CD concentrations, 2:2 at intermediate gamma-CD and singly occupied at high gamma-CD concentrations. The emission of the 1:1 and the singly occupied complexes matches that of the alpha T locally excited state, while the emission spectrum of the 2:2 complexes is that of the alpha T excited dimer. Time-resolved fluorescence shows that the excited dimer is more long-lived than the locally excited state, while transient absorption shows that the alpha T triplet is efficiently quenched by static quenching in the 2:2 complexes. (C) 1997 Elsevier Science B.V.