Torsional Profiles of Thiophene and Furan Oligomers: Probing the Effects of Heterogeneity and Chain Length

Abstract

A systematic analysis of the torsional profiles of 55 unique oligomers composed of two to four thiophene and/or furan rings (n = 2 to 4) has been conducted using three density functional theory (DFT) methods along with MP2 and three different coupled-cluster methods. Two planar or quasiplanar minima were identified for each n = 2 oligomer system. In every case, the torsional angle (τ) between the heteroatoms about the carbon−carbon bond connecting the two rings is at or near 180°for the global minimum and 0°for the local minimum, referred to as anti and syn conformations, respectively. These oligomers have rotational barrier heights ranging from ca. 2 kcal mol −1 for 2,2′-bithiophene to 4 kcal mol −1 for 2,2′-bifuran, based on electronic energies computed near the CCSD(T) complete basis set (CBS) limit. The corresponding rotational barrier for the heterogeneous 2-(2-thienyl)furan counterpart falls approximately halfway between those values. The energy differences between the minima are approximately 2 and 0.4 kcal mol −1 for the homogeneous 2,2′-bifuran and 2,2′-bithiophene, respectively, whereas the energy difference between the planar local and global minima (at τ = 0 and 180°, respectively) is only 0.3 kcal mol −1 for 2-(2-thienyl)furan. Extending these three oligomers by adding one or two additional thiophene and/or furan rings resulted in only minor changes to the torsional profiles when rotating around the same carbon−carbon bond as the two-ring profiles. Relative energy differences between the syn and anti conformations were changed by no more than 0.4 kcal mol −1 for the corresponding n = 3 and 4 oligomers, while the rotational barrier height increased by no more than 0.8 kcal mol −1 .

Correlation of solid-state order to optoelectronic behavior in heterocyclic oligomers

“…This configuration is nearly equal in energy to the transoid configuration (+0.02 kcal mol −1 ), as previously seen in the literature for thiophene/furan oligomers. 38,39 The photophysical properties computed for this cisoid conformer are nearly identical to those reported in Fig. 2a for the transoid global minimum.…”

London Dispersion-Assisted Low-Temperature Gas Phase Synthesis of Hydrogen Bond-Inserted Complexes

“…5 Halogen bonding to the N end of HCN becomes increasingly competitive with hydrogen bonding on increasing the size of the halogen. 6 In aqueous solution, methyl halides have an increasing affinity toward porphyrins and other hosts. 7 In axial–equatorial equilibria of halogenated cyclohexanes, steric and London dispersion contributions compete with each other.…”

Building a Torsional Potential between Thiophene Rings to Illustrate the Basics of Molecular Modeling

“…More specifically, the HF approach overestimates steric hindrance at 0° (S–S interaction) and 180° (S–H interaction), while the DFT approach (B3LYP) reduces the effect of said steric hindrance while increasing the weight of the ∼90° torsional barrier (Table ), mainly due to the distortion on the backbone conjugation . These profiles are similar to those previously reported in the bibliography. , Similarly, the observed changes on the torsional profile shape (i.e., the torsional barriers) because of considering the electronic correlation were also reported by Perkins et al by means of a high level calculation using MP2 and coupled-cluster theory.…”

“…21 These profiles are similar to those previously reported in the bibliography. 23,25 Similarly, the observed changes on the torsional profile shape (i.e., the torsional barriers) because of considering the electronic correlation were also reported by Perkins et al 26 by means of a high level calculation using MP2 and coupled-cluster theory.…”