Effect of local molecular structure on the chain-length dependence of the electronic properties of thiophene-based pi-conjugated systems.
Three series of thiophene-based pi-conjugated oligomers built with different combinations of thiophene cycles and double bonds have been synthesized and characterized. The analysis of the chain length dependence of the electronic, electrochemical, and vibrational properties of the three series of oligomers has been carried out using cyclic voltammetry, UV-vis, IR, and Raman spectroscopies. These various investigations provide consistent results showing that incorporation of ethylenic linkages in an oligothiophene structure leads to a faster decrease of the HOMO-LUMO gap with chain extension due to the combined effects of enhanced planarity and lower overall aromatic character of the system. Although the incorporation of two consecutive double bonds in the system leads to a stabilization of the dicationic state, this structural modification does not produce the expected further decrease of the HOMO-LUMO gap at large chain extension. This phenomenon is discussed on the basis of an interplay between aromaticity and bond length alternation.
Frère
Pierre
P
Groupe Systèmes Conjugués Linéaires, IMMO, UMR CNRS 6501, Université d'Angers, 2 Bd Lavoisier, 49045 Angers, France. pierre.frere@univ-angers.fr
Raimundo
Jean-Manuel
JM
Blanchard
Philippe
P
Delaunay
Jacques
J
Richomme
Pascal
P
Sauvajol
Jean-Louis
JL
Orduna
Jesus
J
Garin
Javier
J
Roncali
Jean
J