Conjugated, rod-like viologen oligomers: Correlation of oligomer length with conductivity and photoconductivity

• Published in: Synthetic metals Vol. 241; pp. 31 - 38
• Main Authors: Chen, Long, Vivier, Elodie, Eling, Charlotte J., Babra, Tahkur S., Bouillard, Jean-Sebastien G., Adawi, Ali M., Benoit, David M., Hartl, František, Colquhoun, Howard M., Efremova, Olga A., Greenland, Barnaby W.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.07.2018; Elsevier BV
• Subjects: Absorption spectra; Band gap; Conductivity; Dimers; Energy gap; Oligomers; Optoelectronic devices; Organic synthesis; Photoconductivity; Photonic band gaps; Spin coating; Thick films; Thin films; Trimers; Viologen; Organic synthesis; Conductivity; Viologen; Photoconductivity
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/j.synthmet.2018.03.019

[Display omitted] •A series of discrete molecular weight conjugated viologen containing oligomers have been synthesised.•The conductivity of the oligomers increases with the degree of oligomerisation.•The oligomer with 3 viologens and 12 aromatic rings in conjugation exhibited photoconductivity in the visible region. An iterative synthesis has been used to produce conjugated, monodisperse, viologen-based aromatic oligomers containing up to 12 aromatic/heterocyclic rings. The methoxy-substituted oligomers were soluble in common organic solvents and could be processed by spin coating. The conductivities of the resulting films (30–221 nm thick) increased by more than one order of magnitude as the oligomer length increased from unimer (1, 2.20 × 10−11 S cm-1) through dimer (2) to trimer (3, 6.87 × 10-10 S cm-1). The bandgaps of the materials were estimated from the absorption spectra of these thin films. The longest oligomer, 3, exhibited a noticeably narrower bandgap (2.3 eV) than the shorter oligomers (1 and 2 both 2.7 eV). Oligomer 3 also showed photoconductivity under irradiation across a wide range of wavelengths in the visible spectral region. In conjunction with DFT calculations of these systems our results suggest that structurally related viologen-type oligomers may find use in optoelectronic devices.