Preparation of a new polymer containing photoluminescent pyrazoline unit in the main chain

A novel photoluminescent polymer (PPyne) containing a 2-pyrazoline unit in the molecular main chain was prepared (for the first time) by polycondensation between a 2-pyrazoline monomer [an adduct of 2,6-bis(4-bromobenzylidene)cyclohexanone with phenylhydrazine] and 2,5-dihexyloxy-p-phe.aylene diboric ester in the presence of Pd(PPh3)(4). PPyne had a number-average molecular weight of 7800 and a polydispersity index of 1.99 and showed good solubility in common organic solvents. In toluene PPyne exhibited an intrinsic viscosity [eta] of 0.42 dL g(-1) at 30 degreesC. The polymer was photoluminescent (PL) in both the chloroform solution and the solid state; the quantum yield of PL in the solution was 40%. In the two states, PPyne gave the same ultraviolet visible (UV-vis) peak at 368 nm and the same PL peak at 512 mn. DSC traces indicated that PPyne had a melting temperature of 168 degreesC, and thermogravimetric analysis revealed that the polymer had good thermal stability with a 5 wt % loss temperature of 376 degreesC under N-2. Electrochemical oxidation of PPyne started at about 0.5 V versus Ag/AgNO3 and gave a peak at 0.98 V versus Ag/AgNO3 with a color change of the film from yellow to black green. The color change was followed by UV-vis spectroscopy. The corresponding reduction peak appeared at 0.80 V versus Ag/AgNO3 Treatment of PPyne with HCl led to dehydrogenating transformation of the polymer to a new cross-conjugated polymer. (C) 2004 Wiley Periodicals, Inc.