Synthesis of π-Conjugated Poly(cyclodiborazane)s by Organometallic Polycondensation

Abstract

Donor−acceptor type π-conjugated poly(cyclodiborazane)s were synthesized by organometallic polycondensation between cyclodiborazane-containing dibromide and 2,5-didodecyloxy-1,4-diethynylbenzene utilizing Sonogashira coupling. The polymerization was carried out under a nitrogen atmosphere, in THF/NEt3 solution in the presence of a catalytic amount of copper acetate, palladium chloride, and triphenylphosphine at 80 °C for 12 h. After reprecipitation into MeOH, the resulting polymer was isolated as a brown powder in moderate yield. The polymer obtained was soluble in common organic solvents such as THF, chloroform, and benzene, and its structure was confirmed by 1H NMR, 11B NMR, and IR spectra. The number-average molecular weight of the polymer was 8500 from the gel permeation chromatographic analysis (GPC, THF, PSt standards). In the UV−vis absorption spectrum recorded in chloroform, the absorption maximum was observed at 414 nm, owing to extension of π-conjugation via the vacant p-orbital of the boron atom and intramolecular charge transferred structure. This polymer exhibited an intense blue-green light emission upon irradiation at 414 nm.