| Abstract
| - Crown-annelated quater- (4T) and sexithiophenes (6T) with oligooxyethylene chains of variouslengths attached at the 3-positions of the terminal thiophene rings have been synthesized. Analysis of thecation-binding properties of the macrocycles by 1H NMR and UV−vis spectroscopy reveals the formationof a 1:1 complex with Ba2+, Sr2+, or Pb2+ and shows that cation complexation results in a conformationaltransition in the π-conjugated system. Theoretical analysis of this process by density functional methodspredicts that this conformational transition results in a narrowing of the highest occupied−lowest unoccupiedmolecular orbital gap of the conjugated system with a decrease of the redox potentials (E01 and E02)associated with the formation of the 4T cation radical and dication. Cyclic voltammetry shows that, dependingon the binding constant, the presence of metal cation produces a negative or a positive shift of E01 whileE02 always shifts negatively. This unusual behavior is discussed in terms of interplay between electrostaticinteractions and conformational changes associated with cation binding.
|
