Solution‐Processible Blue‐Light‐Emitting Polymers Based on Alkoxy‐Substituted Poly(spirobifluorene)

Alkoxy‐substituted poly(spirobifluorene)s and their copolymers with a triphenylamine derivative have been synthesized by Ni(0)‐mediated polymerization. The polymers were well soluble in common organic solvents. Pure blue‐light emissions without the long wavelength emission of poly(fluorene)s have been observed in the fluorescence spectra of polymer thin films. The light emitting diodes with a device configuration of ITO/PEDT:PSS(30 nm)/polymer(60 nm)/LiF(1 nm)/Al(100 nm) have been fabricated. The electroluminescence spectra showed the blue emissions without the long wavelength emission as observed in the fluorescence spectra. The relatively poor electroluminescence quantum yield of the homopolymer (0.017% @ 20 mA/cm²) with color coordinates of (0.16, 0.07) has been improved by the introduction of triphenylamine moiety, and the copolymer with triphenylamine derivative exhibited an electroluminescence quantum yield of 0.15 % at 20 mA/cm² with color coordinates of (0.16, 0.08). Moreover, the introduction of polar side chains to the spirobifluorene moiety enhanced the device performance and led to the quantum yields of 0.6 to 0.7 % at 20 mA/cm², although there was some expense of color purities.