Experimental and computational studies of substituted terthiophene oligomers as electroluminescent materials

Density functional calculations at the B3LYP/6-31 G(d) level are used to predict the vibrational spectra for a series of substituted thiophenes and terthiophenes containing the emitter unit diethenyl benzene (DEB). The calculations show that cyano substitution induces non-planarity, particularly for the terthiophene compound. This was verified by the absorption and emission data, which suggest that the ground state is less planar than the excited state. The solution phase electronic spectroscopy reveals that some of the compounds are very emissive; however, CN substitution quenches this emission. Electroluminescent devices may be constructed using these emitter materials and it is found that the efficiency of the CNDEB compounds may be improved with the introduction of a different hole transporting layer.