We present the optical and electronic properties of a new laddertype poly(paraphenylene) (LPPP), the m-LPPP, having the highest intramolecular order and highest environmental stability in the familiy of the LPPPs up to now. The m-LPPP is an excellent candidate for the usage as an active layer in electroluminescence (EL) devices, due to its well defined structure and high purity, as the spectral behaviour of the absorption coefficient cc confirms. cx is very low (αmin <12 cm−1) in the subgap region with a steep onset to the interband transition leading to welir"resolved vibrationally split maxima (αmax ≈ 1.1×105 cm−1). Moreover, the high quantum efficiency of fluorescence (up to 30 % in films) makes the m-LPPP a promising material for high efficiency-EL devices.
The polymer-light emitting diodes (PLEDs), which were fabricated in air stable sandwich structures ITO/m-LPPP/Al, are characterized by high quantum efficiencies up to 4% and cwoperation lifetimes around 170 h. The PLEDs produced homogeneous bright light in the blue and blue-yellow spectral range, with the dominant emission maximum located at 461 nm. The onset field significantly depends on the thickness of the m-LPPP layers (Emin ≈ 0.5 MV/cm; Emax ≈ 2.6 MV/cm) due to ordering effects in the cast polymer. In the blue-green spectral range, the shape of the EL spectra and hence the emission colour can be controlled, by varying the applied electric field.