Conformational properties of thiophene oligomers

Abstract

The molecular geometries and the torsional potentials about the inter‐ring C‐C bond in α‐oligothiophenes (α‐nTh, n=2–4) have been calculated by means of conventional ab initio and density functional theory (DFT) calculations employing the hybrid B3LYP and BH&HLYP functionals. The position and the energetics of the critical points in the potential energy curve generated by rotation about the inter‐ring CC bond are shown to be dependent on the computational method. DFT calculations, in comparison with MP2 calculations, favour conjugative interactions, while steric and coulombic interactions are equally treated by both methods. On oligomerization the electron delocalisation increases slightly, the p‐charge being preferentially confined within the rings, although it is sufficient to move the molecular structure towards co‐planarization and to increase the barrier through the perpendicular conformation. The IR and Raman spectra on the relevant rotamers of α‐2Th have been computed at HF/6–31G* and B3LYP/6–31G* levels. The comparison with the experiment is excellent. It has been found that small twisting from the planar conformation has no apparent effects, while 90° twisting and isomerization to the syn‐gauche form produce significant frequency and intensity variations which could be useful probes in conformational studies. The simulated IR and Raman spectra of the α‐2Th rotamers are consistent with a smallπ‐electron delocalisation between the rings.

Polaron Pair versus Bipolaron on Oligothiophene Chains: A Theoretical Study of the Singlet and Triplet States

“…This choice of functionals is suggested by the excellent results obtained for the structures of polyenes [26] and neutral oligothiophenes. [27] For the www.chemphyschem.org…”

“…[9±12, 21] Considering the multistep synthesis and consequently high price of the mesogenic acrylate components, it is of great interest to replace part of the mesogenic component with a reactive solvent, thus obtaining a crosslinkable lyotropic system. Lyotropic cholesteric systems are less common and based on cellulose, [22±25] polyisocyanate, [26] or poly(L-glutamic acid) [27] systems. However, in cellulose systems, the reflection wavelength depends on the degree of polymerization, the solvent, solvent concentration and, most detrimentally, on the temperature.…”

Oligothiophene radical cations: Polaron structure in hybrid DFT and MP2 calculations

“…The large size of the systems of interest makes the use of DFT methods attractive. Hybrid functionals, combining Hartree–Fock (HF) exchange with various density functionals for exchange and correlation, are being actively explored and exploited in DFT calculations; their performance for π‐conjugated systems can be remarkable 7, including the case of neutral oligothiophenes 8. Nevertheless, the reliability of hybrid DFT methods has not been firmly established yet, especially in complex cases.…”

Two-photon Photoemission of Organic Semiconductor Molecules on Ag(111)

“…In the tilted monolayer, a peak at 0. source for the quaterthiophene was Sigma-Aldrich, and the rotational barrier around the C-C bond is estimated to be 40 meV -150 meV, depending on the basis set used in DFT calculations [102]. The temperatures for the effusion cell were 150 • C and 160 • C, and the possibility that the conformation changed while dosing cannot be ruled out.…”