On the Inter-Ring Torsion Potential of 2,2′-Bithiophene: A Review of Open Problems and Current Proposals

Abstract

In this review, we describe the results of the most important theoretical studies of rotation around the bond connecting two thiophene rings in 2,2ʹ-bithiophene. The review first summarizes the earlier studies (since late 1960s), in which the most energetically favourable conformations of the molecule have been characterized for the first time. It then examines the one-dimensional potentials of internal rotation calculated using semiempirical, Hartree-Fock (HF), post-Hartree-Fock methods, and Kohn-Sham density functional theory (throughout the 1990s to the present), as well the torsion potential functions V(θ). Three directions in recent studies are highlighted: (i) the development and testing of force fields supplemented with new parameters of torsion interactions in thiophene-containing materials, (ii) the application of new hybrid, exchange-correlation and long-range corrected functionals for describing the inter-ring rotation and through-space (non-valent) intramolecular interactions which stabilize either cis (syn)- or trans (anti)-rotamer, and (iii) the torsion-dependent properties of bithiophene-containing systems. A concluding part gives a brief outlook on further studies in the field and offers a road map for novel research directions that are required to realize new breakthroughs in thiophene-based device performance in the future.