Pi-Dimerization of Oligothienoacene Radical Cations

Abstract

Oligothienoacenes, the fused-ring analog of -linked oligothiophenes, belong to the most promising candidates for organic electronic applications. This is in part due to their densely packed solid-state structures resulting in high charge carrier mobilities.1 In recent years, there has been a growing interest in the study of the -dimerization of conjugated radical cations with a dual purpose: (i) elucidation of the nature of the charge-transport phenomena in -doped semiconducting polymers and (ii) development of supramolecular bonding ideas for applications in material science.2 However, the π-dimerization of planar conjugated radical cations in solution is scarce and usually encountered at low temperatures. In this work, the exceptional -dimerization capability showed by radical cations of oligothienoacenes is investigated for the first time. To this end, we make use of a joint experimental and theoretical approach that combines different spectroscopic techniques with advanced DFT calculations. Our results evidence that the incorporation of bulky TIPS groups prevents the -dimerization while the ,-substitution with n-decyl groups in heptathienoacene or -substitution with thienyl groups in tetrathienoacene favors the -dimer formation.3 The nature, structure and stability of the different aggregate structures formed in the course of the oxidation are rigorously analyzed with the help of exhaustive DFT and TD-DFT calculations.