Synthesis, characterization and theoretical studies of thiophene/phenylene derivatives as electroluminescent materials

Metal catalyzed cross coupling reaction have been employed to synthesize the four ring thiophene/phenylene compounds, 4,4′-bis(3-octylthienyl)biphenyl (OTBP) and 4,4′-bis(thienyl)biphenyl (BTBP). Compound OTBP crystallizes in the triclinic system with the phenyl rings almost coplanar and the dihedral angle of thiophene ring with the phenyl group is 37°. The molecule has an inversion center in the middle of the two phenyl groups. In the crystalline space the structure is stabilized by Van der Waals forces between the zig-zag carbon chains. The influence of the alkyl group on the geometry and coplanarity of the structures is discussed on the evidence of the spectroscopic results. These compounds have been fully characterized by 13C NMR, 1H NMR FT-IR, UV/visible spectroscopy. The results from fluorescence and X-ray crystallography structure analysis are reported. Ab-initio calculations of the ground state geometries of both molecules consider Hartree-Fock (HF) and Density Functional Theory (DFT) methodologies. In both cases, the 6-31G+(d, p) basis set was chosen and the B3LYP hybrid functional for correlation and exchange in the DFT calculations.