jp060254s_si_003.pdf (595.71 kB)
Structural Control of the Electronic Properties of Photodynamic Azobenzene-Derivatized π-Conjugated Oligothiophenes
journal contribution
posted on 2006-03-16, 00:00 authored by Bruno Jousselme, Philippe Blanchard, Magali Allain, Eric Levillain, Marylène Dias, Jean RoncaliQuaterthiophenes containing a median 3,3‘-dimethoxybithiophene (4MTZ) or bis(3,4-ethylenedioxythiophene)
(4ETZ) block and an azobenzene group attached at two internal β-positions of the end thiophene rings have
been synthesized. The analysis of the crystal structure of the two compounds by X-ray diffraction shows that,
for 4MTZ, the quaterthiophene chain adopts a syn−anti−syn conformation similar to the parent system based
on unsubstituted quaterthiophene. In contrast, 4ETZ presents an all-anti conformation stabilized by noncovalent
intramolecular interactions between oxygen atoms and thiophenic sulfur atoms. The effect of the photoisomerization of the azobenzene group on the electronic properties of the attached π-conjugated quaterthiophene
chain has been analyzed by UV−vis spectroscopy and cyclic voltammetry. The results obtained for 4MTZ
suggest very limited geometrical changes due to the restricted rotation around the central interannular single
bond caused by steric interactions between the methoxy groups. In contrast, upon trans to cis photoisomerization
of the attached azobenzene group of 4ETZ, the quaterthiophene chain undergoes a reversible conformational
switch to a final state with a lower HOMO level and a larger HOMO−LUMO gap than the initial state.