Energy transfer study of symmetric polyisoprene-poly(methyl methacrylate) diblock copolymers bearing dyes at the junctions: Dye orientation

Direct nonradiative energy transfer experiments are described for the lamellar structures formed in films of poly(isoprene-b-methyl methacrylate) in which individual polymers are labeled at the junction with a single dye molecule. The donor was 9-phenanthryl (9Phe), and we compare two acceptors (1-anthryl (1An) and 2-anthryl (2An)) which differ in the orientation of their transition moments with respect to the polymer backbone. Experiments on the lamellar structures formed in films of PI-9Phe-PMMA/PI-1An-PMMA and PI-9Phe-PMMA/PI-2An-PMMA provide identical values of the interface thickness (1.1 +/- 0.2 nm) between the PI and PMMA domains. The fact that a common value is obtained for the two sets of experiments indicates that the orientation parameter kappa(2) for the energy transfer process in this rigid system makes an identical contribution to both sets of experiments. We take these results as justification for using an averaged value of the orientation parameter <\kappa\>(2) in fitting experimental data to the underlying theory of energy transfer. We find that in our experiments the local correlation in orientation of the polymer chains in the region of the interface is too small to be detected.