Poly( meta-phenylene) derivative with rigid twisted biphenyl units in backbone:: Synthesis, structural characterization, photophysical properties and electroluminescence

A soluble poly (meta-phenylene) derivative with rigid twisted biphenyl unit was synthesized by the Yamamoto coupling reaction. The polymer is soluble in common organic solvents, and the number-average molecular weight is about 6500. The UV-Vis and quantum chemical calculation indicate that the different conformation segments named '' conformers '' exist in the polymer backbones; it was also further confirmed by the single crystal X-ray diffraction study of the dimeric model compound. The pi-pi* transition of biphenyl segments of twisted and planar conformations made the polymer exhibit a strong absorption around 256 nm and a weak absorption at about 300 nm. Furthermore, the polymer exhibits a strong UV photoluminescence at 372 nm when the excitation wavelengths are longer than 300 nm. The ultraviolet-emitting electrolumineseence(EL) device with the single layer structure shows EL lambda(max) of the derivative at 370 nm.