Observation of α-terthiophene excited dimer fluorescence in aqueous solutions of γ-cyclodextrin

The photophysical properties of inclusion complexes formed with γ-cyclodextrin (γ-CD) as host and 2,2′:5′,2″-terthiophene (αT) as guest have been investigated. The host:guest complexes formed at αT concentration are 1:1 at low γ-CD concentrations, 2:2 at intermediate γ-CD and singly occupied at high γ-CD concentrations. The emission of the 1:1 and the singly occupied complexes matches that of the αT locally excited state, while the emission spectrum of the 2:2 complexes is that of the αT 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 αT triplet is efficiently quenched by static quenching in the 2:2 complexes.