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J Phys Chem Lett. 2015 Sep 17;6(18):3521-7. doi: 10.1021/acs.jpclett.5b01410. Epub 2015 Aug 27.

Resonance Raman Spectroscopy of the T1 Triplet Excited State of Oligothiophenes.

Author information

1
Department of Chemistry & Biochemistry, University of California at San Diego , La Jolla, California 92093, United States.
2
Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States.
3
Department of Chemistry, Rice University , Houston, Texas 77251, United States.

Abstract

The characterization of triplet excited states is essential for research on organic photovoltaics and singlet fission. We report resonance Raman spectra of two triplet oligothiophenes with n-alkyl substituents, a tetramer and hexamer. The spectra of the triplets are more complex than the ground state, and we find that density functional theory calculations are a useful starting point for characterizing the bands. The spectra of triplet tetrathiophene and hexathiophene differ significantly from one another. This observation is consistent with a T1 excitation that is delocalized over at least five rings in long oligomers. Bands in the 500-800 cm(-1) region are greatly diminished for an aggregated sample of hexathiophene, likely caused by fast electronic dephasing. These experiments highlight the potential of resonance Raman spectroscopy to unequivocally detect and characterize triplets in thiophene materials. The vibrational spectra can also serve as rigorous standards for evaluating computational methods for excited-state molecules.

KEYWORDS:

Polythiophene; aggregate; hexathiophene; quaterthiophene; sexithiophene; tetrathiophene; vibration

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