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Thiophene- and Selenophene-Based Heteroacenes:  Combined Quantum Chemical DFT and Spectroscopic Raman and UV−Vis−NIR Study

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posted on 05.07.2007 by Reyes Malavé Osuna, Rocío Ponce Ortiz, Toshihiro Okamoto, Yoshitake Suzuki, Shigehiro Yamaguchi, Víctor Hernández, Juan Teodomiro López Navarrete
In this article, we report the characterization of a series of thiophene- and selenophene-based heteroacenes, materials with potential applications in organic electronics. In contrast to the usual α-oligothiophenes, these annelated oligomers have a larger band gap than most semiconductors currently used in the fabrication of organic field-effect transistors (OFETs) and therefore they are expected to be more stable in air. The synthesis of these fused-ring molecular materials was motivated by the notion that a more rigid and planar structure should reduce defects (such as torsion about single bonds between α-linked units or S-syn defects) and thus improve π-conjugation for better charge-carrier mobility. The conjugational properties of these heteroacenes have been investigated by means of FT-Raman spectroscopy, revealing that π-conjugation increases with the increasing number of annelated rings. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G** level, to assess information regarding the minimum-energy molecular structure, topologies, and absolute energies of the frontier molecular orbitals around the gap, vibrational normal modes related to the main Raman features, and vertical one-electron excitations giving rise to the main optical absorptions.

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