Studies on the Structures and Spectra of Benzothiophene Oligomers

Theoretical studies on a series of oligobenzothiophenes were carried out with the AM1 and DFT methods. Based on B3LYP/6-31G(D) optimized geometries, the electronic spectra,IR spectra and NMR spectra of the oligomers were calculated by INDO/CIS, AM1 and B3LYP/6-31G(D) methods, respectively. The energy gaps decrease, and the absorption in electronic spectra exhibits a red-shift as polymerization increases. The IR frequencies are little affected by the polymerization and substituents. The 13C chemical shifts are changed to be upfield since the electron-donating groups increase the electron density of carbon atoms but remain unchanged with the increase of polymerization.