Synthesis of π-conjugated poly(cyclodiborazane)s by organometallic polycondensation

Donor-acceptor type pi -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 degreesC 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 H-1 NMR, B-11 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 pi -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.