Web Release Date: July 13,
Exploration of Ground and Excited Electronic States of Aromatic and Quinoid S,S-Dioxide Terthiophenes. Complementary Systems for Enhanced Electronic Organic Materials
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Contribution from the Steacie Institute for Molecular Sciences, National Research Council of
Canada, K1A 0R6, Ottawa, Canada, Department of Chemistry, University of Minnesota,
Minneapolis, Minnesota 55455, Division of Science and Mathematics, University of Minnesota,
Morris, Minnesota 56267, Istituto CNR di Scienze e Tecnologie Molecolari, via C. Golgi 19,
20133 Milano, Italy, Department of Organic Chemistry, University of M
laga, Campus de
Teatinos s/n, Mlaga 29071, Spain, and Department of Physical Chemistry, University of
Mlaga, Campus de Teatinos s/n, Mlaga 29071, Spain
Received February 27, 2006
Abstract:
We analyze the electronic and molecular structures for the ground and excited electronic states
of aromatic terthiophene (3T), the quinodimethane 3',4'-dibutyl-5,5' '-bis(dicyanomethylene)-5,5' '-dihydro-2,2':5',2' '-terthiophene (3Q), and isologues with the middle ring S-oxidized (3TO2, 3QO2). These represent
extremes of electron rich and deficient ground states, often exhibiting complementary properties. Oxidizing
the central sulfur atom affects the molecular structure, electron affinity, and photophysical properties of
both 
systems. The consequences for 3T include de-aromatization of the central thiophene, red-shifting
of the electronic absorption spectrum, and lowering of the reduction potential. The electron deficient quinoid
3QO2 shows an enhancement of electron affinity from reducing the electron-donor ability of sulfur, and a
blue-shifting of its electronic absorption spectrum was seen. Fluorescence emission is quenched in the
sulfonated terthiophene, and the contrary effect again would be expected upon sulfonation of a quinoid
emitter. Raman vibrational spectroscopy, electrochemistry, and UV-vis and fluorescence spectroscopies
are analyzed in conjunction with theoretical calculations.
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