Self-Assembly, Molecular Ordering, and Charge Mobility in Solution-Processed Ultrathin Oligothiophene Films

Published

November 29, 2005

Author(s)

A R. Murphy, Paul C. Chang, Priscilla VanDyke, J Liu, J M. Frechet, V Subramanian, Dean DeLongchamp, S Sambasivan, Daniel A. Fischer, Eric K. Lin

Abstract

Symmetrical quarter-(T4), penta-(T5), sexi-(T6), and heptathiophene (T7) oligomers containing thermally removable aliphatic ester solubilizing groups were synthesized, and their UV-vis and thermal characteristics were compared. Spun-cast thin films of each oligomer were examined with atomic force microscopy and near-edge X-ray absorption fine structure spectroscopy to evaluate the ability of the material to self-assemble from a solution-based process while maintaining complete surface coverage. Films of the T5-T7 oligomers self-assemble into crystalline terraces after thermal annealing with higher temperatures required to affect this transformation as the size of the oligomers increases. A symmetrical ,-substituted sexithiophene (T6-acid) that reveals carboxylic acids after thermolysis was also prepared to evaluate the effect of the presence of hydrogen-bonding moieties. The charge transport properties for these materials evaluated in top-contact thin film transistor devices were found to correlate with the observed morphology of the films. Therefore, the T4 and the T6-acid performed poorly because of incomplete surface coverage after thermolysis, while T5-T7 exhibited much higher performance as a result of molecular ordering. Increases in charge mobility correlated to increasing conjugation length with measured mobilities ranging from 0.02 to 0.06 cm2/(V·s). The highest mobilities were measured when films of each oligomer had an average thickness between one and two monolayers, indicating that the molecules become exceptionally well-ordered during the thermolysis process. This unprecedented ordering of the solution-cast molecules results in efficient charge mobility rarely seen in such ultrathin films.

Citation

Chemistry of Materials

Pub Type

Journals

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Keywords

NEXAF, oligothiophene, orgainc electronics, sexithiophene, x-ray absorption spectroscopy

Citation

Murphy, A. , Chang, P. , VanDyke, P. , Liu, J. , Frechet, J. , Subramanian, V. , DeLongchamp, D. , Sambasivan, S. , Fischer, D. and Lin, E. (2005), Self-Assembly, Molecular Ordering, and Charge Mobility in Solution-Processed Ultrathin Oligothiophene Films, Chemistry of Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852479 (Accessed December 13, 2024)