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RESEARCH PRODUCT

Electronic Spectra of 2,2‘-Bithiophene and 2,2‘:5‘,2‘ ‘-Terthiophene Radical Cations:  A Theoretical Analysis

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Analysis of the electronic spectra of 2,2‘-bithiophene and 2,2‘:5‘,2‘ ‘-terthiophene radical cations has been performed by using multiconfigurational second-order perturbation theory (CASPT2). Atomic natural orbital (ANO) type basis sets of split valence quality, including polarization functions on all heavy atoms, have been used. In agreement with experimental data, in the energy range below the lowest optically allowed transition of the respective neutral system, theoretical results predict two main absorption bands for both cations. The 22Au and 32Au states computed at 1.94 and 2.80 eV, respectively, are related to the corresponding band maxima recorded for bithiophene cation. The 12B1 state of terthiophene cation placed at 1.31 eV is assigned to the observed lowest-energy band. Nevertheless, according to the present results, the highest-energy band observed in terthiophene cation stems from two electronic transitions. They involve the 22B1(1.94 eV) and 32B1(2.12 eV) excited states.