Time-resolved emission anisotropy of anthracene fluorophore in the backbone of stereoregular poly(methyl methacrylate)

Syndiotactic fluorescent poly(methyl methacrylate) labeled with anthracene in the middle of the polymer chain was prepared by living anionic polymeriz ation (s-PMMA-A). Absorption and emission transition moments of the label a re oriented in the direction of the polymer backbone, therefore the fluorop hore really reflects the mobility of polymer segments. Stereocomplex format ion between isotactic poly(methyl methacrylate) (i-PMMA) and s-PMMA-A was s tudied by time-resolved fluorescence depolarization method in solvents with different complexing ability and at different i-PMMA/s-PMMA-A ratios. The stoichiometry of the stereocomplex i-PMMA/s-PMMA-A was 1/2 and 1/1.5 in N,N -dimethylformamide and 1,4-dioxane, respectively. The stereocomplex was not formed in chloroform. Determination of the rotational correlation times at different temperatures enabled us to evaluate the height of the potential barrier to rotational motion of the anthracene fluorophore (DeltaU(r)) or a ctivation enthalpy and entropy (DeltaH(not equal), DeltaS(not equal)) of th is process in the presence and absence of the stereocomplex. Time-resolved emission anisotropy data, r(t), were analyzed by intermediate zone formula of the torsion dynamics theory for stiff macromolecules. The torsional rigi dity of the stereocomplex i-PMMA/s-PMMA-A, a = 1.9 x 10(-18) N . m in N,N-d imethylformamide at 30 degreesC, is larger than that obtained for DNA (a = 3.8 x 10(-19) N . m). Self-aggregation of s-PMMA takes place probably in N, N-dimethylformamide.