FLUORESCENCE STUDIES OF POLY(P-PHENYLENEETHYNYLENE)S - THE EFFECT OF ANTHRACENE SUBSTITUTION

The poly(p-phenylezthynylene) molecules, PI-PIII, synthesized by a pal ladium-catalyzed cross-coupling reaction of diiodobenzene derivatives and derivatives of 1,4-diethynylbenzene, are highly luminescent materi als. The polymers are soluble by virtue of the -OC16H33 groups introdu ced on the aromatic rings and by controlling their molecular weight. T he fluorescent quantum yields are between 0.35 and 0.40 depending on t he material. The excited-state Lifetimes of the polymers are 1-2 ns, s lightly shorter than that of the model compound, 1,4-diphenylethynyl-2 ,5-dibutoxybenzene, which has a lifetime of 3 ns. Incorporation of ant hracene, coupled at the 9,10-positions by using 9,10-bibromoanthracene , into the polymer backbone decreases the quantum yield to between 0.0 5 and 0.27 depending on the anthracene content. In addition, low-energ y electronic transitions and longer wavelength emission bands associat ed with the anthracene group are produced. The polymers harvest optica l energy and transfer it to the anthracene resulting in emission from this chromophore. In the case where only terminal anthracene units, in troduced by using 9-bromo-10-phenylethynylanthracene, are present, the process is very efficient with >95% of the energy being transferred t o the end groups.