π-Conjugated Polyphenylenes with Diazaborole Side Chains Synthesized via 1,2-Phenylenediamine Polymer

Abstract

Pd-complex-catalyzed polycondensation of 3,6-dibromo-1,2-phenylenediamine (1) with 2,7-bis(1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (2) gave polymer 1a which consisted of 1,2-phenylenediamine-3,6-diyl and 9,9-dioctylfluorene-2,7-diyl units in 99% yield. Polymer 1a showed a weight-average molecular weight (Mw) of 78 000 in the light scattering analysis and gave an intrinsic viscosity of 0.74 dL g-1. Reaction of polymer 1a with aromatic boronic acids, Ar−B(OH)2 (Ar = C6H5, C6H4-p-Bu, and C6H4-p-OMe), provided polymers 2a−2c with a diazaborole ring in the side chain. A model compound of polymer 1a, [1,4‘;1‘,1‘ ‘;4‘ ‘,1‘ ‘‘;4‘ ‘‘,1‘ ‘‘ ‘]quinquephenyl-2‘ ‘,3‘ ‘-diamine (model compound 1), was also prepared by Pd-complex-catalyzed reaction of 1 with biphenyl-4-boronic acid. Structures of the polymers and the model compound were determined by 1H NMR and IR spectroscopy as well as by elemental analyses. All the polymers and the model compound were photoluminescent in solution, and introduction of the diazaborole ring enhanced intensity of photoluminescence (PL). Cyclic voltammetry revealed that all the polymers and the model compound were electrochemically active in solutions, and the phenylenediamine and benzodiazaborole units behave as an electron-donating group. Thermal stability of polymer 1a was improved by transformation of the diamino group to the diazaborole side chain.