Study of the interactions between substituted 2,2′-bithiophenes and cyclodextrins

The interactions of 4,4′-dimethoxy-2,2′-bithiophene (DMO44BT), 4,4′-dibutoxy-2,2′-bithiophene (DBO44BT), and 2,2′-bithiophene (BT) with α- and/or β-cyclodextrins (CD) were investigated by absorption and steady-state fluorescence spectroscopy. The absorption spectra in all cases are only slightly shifted going from water to the CD cavity showing that the ground state conformations of the bithiophenes in the CD cavity remain similar to that found in water. From fluorescence measurements, it was found that DMO44BT and DBO44BT form 1:2 (guest:host) complexes with α-CD, while DMO44BT and BT form 1:1 complexes with β-CD. The nature of the interactions involved in the inclusion complexes are discussed.