Self-assembly of polypeptide/pi-conjugated polymer/polypeptide triblock copolymers in rod-rod-rod and coll-rod-coil conformations

Self-assembly in the bulk of a series of hybrid triblock copolymers formed by a poly(9,9-dihexylfluorene-2,7-diyl) (PHF) middle block and two poly(gamma-benzyl-L-glutamate) (PBLG) end blocks has been studied. Since the alpha-helical secondary structure of the PBLG block may be either maintained or suppressed depending on the solvent casting history, the PBLG-PHF-PBLG copolymers exhibit two different conformations: a rod-rod-rod or coil-rod-coil configuration, respectively. In order to provide insight into the influence of conformation on self-aggregation of these systems, three copolymers with different block ratio were investigated in both conformations using small- and wide-angle scattering techniques and transmission electron microscopy. Time-resolved photoluminescence measurements were performed on the same samples to explore the effect of morphology on photophysical properties. The observed photoluminescence spectra and dominant excited lifetimes of the poly(9,9-dihexylfluorene-2,7-diyl) block were found to differ markedly in rod-rod-rod and coil-rodcoil configurations and were correlated to the morphology of the self-assembled triblock copolymers.