Conformational analysis of 2,2′-bithiophene under interaction of external electric field defined by point charges

Conformational analysis of 2,2′-bithiophene (BT) under the influence of an electric field (EF) constructed by point charges has been performed by using semi-empirical Austin Model 1 (AM1) and Parametric model number 3 (PM3) calculations. When the EF perpendicular to the molecular conjugation chain is applied, both AM1 and PM3 calculations show an energy increase of the anti-conformation. AM1 predicts that the global minimum shifts to syn-conformation when the EF strength is larger than a critical value, and PM3 predicts that the local minimum in anti-conformation vanishes. This kind of EF effect has been ascribed to the EF and dipole moment interaction.