Novel blue photoluminescent copolymers containing bipyridine and organosilicon

Two novel bipyridine- and silicon-containing PPV-based copolymers (P1 and P 2) having the same structure but different molecular weights were synthesiz ed by the Wittig reaction between an organosilicon monomer and two differen t bipyridine monomers. 5,5'-bis(diethyl phosphinatylmethyl)-2,2'-bipyridine and 5,5'-bis(triphenylphosphoniomethyl)-2,2'-bipyridine dibromide were use d as the bipyridine reagents. The former gave copolymer P1 with a higher mo lecular weight (M-n = 9299) than the latter (M-n = 5051), which was respons ible for the poorer solubility in common organic solvents. Thermal analysis (TGA) shows that P2 starts to decompose at ca. 340 degrees C in nitrogen. A glass transition temperature (T-g) of 88.6 degrees C was observed by DSC analysis. UV-vis spectra show that there is no obvious change between the p olymer in solution and as films for P2 while 6 nm of red-shift was noted fo r P1 in the film state. PL spectra reveal that the polymers as films emit a t much longer wavelength than that in CHCl3 solution. The bathochromic effe ct for P1 is larger than that for P2, which results in green emission as fi lms. The redox behavior of the two polymers was investigated by cyclic volt ammetry (C-V), which demonstrates irreversible n-doping and p-doping proces ses. The band gaps of the polymers were estimated from both the optical met hod and electrochemical measurements. (C) 2000 Elsevier Science S.A. All ri ghts reserved.