Crown-annelated oligothiophenes as model compounds for molecular actuation.
Crown-annelated quater- (4T) and sexithiophenes (6T) with oligooxyethylene chains of various lengths attached at the 3-positions of the terminal thiophene rings have been synthesized. Analysis of the cation-binding properties of the macrocycles by (1)H NMR and UV-vis spectroscopy reveals the formation of a 1:1 complex with Ba(2+), Sr(2+), or Pb(2+) and shows that cation complexation results in a conformational transition in the pi-conjugated system. Theoretical analysis of this process by density functional methods predicts that this conformational transition results in a narrowing of the highest occupied-lowest unoccupied molecular orbital gap of the conjugated system with a decrease of the redox potentials (E(0)(1) and E(0)(2)) associated with the formation of the 4T cation radical and dication. Cyclic voltammetry shows that, depending on the binding constant, the presence of metal cation produces a negative or a positive shift of E(0)(1) while E(0)(2) always shifts negatively. This unusual behavior is discussed in terms of interplay between electrostatic interactions and conformational changes associated with cation binding.
Jousselme
Bruno
B
Groupe Systèmes Conjugués Linéaires, UMR CNRS 6501, Université d'Angers, 2 Boulevard Lavoisier, 49045 Angers, France.
Blanchard
Philippe
P
Levillain
Eric
E
Delaunay
Jacques
J
Allain
Magali
M
Richomme
Pascal
P
Rondeau
David
D
Gallego-Planas
Nuria
N
Roncali
Jean
J