The structure and excited state properties of oligothiophenes, OTn (n=2-6), have been studied with semi-empirical (AM1; PM3; PM6) and ab initio (HF; DFT with B3LYP, BVP86, M06-2X functionals) quantum chemistry methods. The present study provides geometry analysis of the neutral and ionic species for optimized ground and excited state structures, employing constrained optimization, and examines the excited state properties, in terms of the transition density and charge difference density. Local minimum of energy in S0 is found when dihedral angle between two thiophene units is 30-50 degree out of plane for neutral species, and when molecule is planar in ionized species and the excited state. BVP86 functional shows the best results for ionic species, whereas M062X reproduced well experimental emission spectra. These studies provide useful information on the utility and the potential problems in using the semi-empirical methods for larger oligomers, and how structural details influence excitation energies.

Computational study of small oligothiophenes:   Structure and excited state properties

244th National Meeting (2012)

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