Novel blue light emitting poly(N-arylcarbazol-2,7-ylene) homopolymers:: Syntheses and properties

In this paper, we synthesized a new type of poly(N-phenyl-2,7-carbazole)s with alkoxy groups or a diphenylamino group at o-, m-, or p- position of the N-phenyl group using the Ni(0)-catalyzed Yamamoto polymerization in high yields. The series of structural isomers were synthesized in order to optimize the inter- and intramolecular interactions. The electron-rich triethylene oxide groups or the triphenylamino groups were introduced to tune the HOMO energy levels. These polymers were characterized by H-1 NMR, C-13 NMR, IR, elemental analysis, GPC, TGA, UV-vis, fluorescence spectroscopy, and electrochemical analysis. All the polymers had enough high molecular weights to show a good solubility in common organic solvents and a good processability for making thin films. Deiodination of the terminal residual iodide of the polymers enhanced the fluorescent quantum yields in CHCl3 (phi(f) (sol) = 0.8). In the form of thin films, all the polymers displayed the fluorescence charts with emission bands around 430, 455, and 475 nm. Among the polymers, PmDPAC, PmpEHOC, PoDPAC, PopEHOC remarkably fluoresced blue (phi(f) (film) > 0.2). The strong fluorescence band around 430 nm for PmpEHOC and PoDPAC suggested a poor visibility, and 475 nm for PopEHOC resulted in an impure blue color emission, while the strong emission band around 455 nm for PmDPAC was appropriate for pure blue emission. Furthermore, the series of PDPAC polymers possessed higher HOMO energy levels than the other carbazole homopolymers.