ELECTROACTIVE AND PHOTOACTIVE ROD-COIL COPOLYMERS - DESIGN, SYNTHESIS, AND SUPRAMOLECULAR REGULATION OF PHOTOPHYSICAL PROPERTIES

Two series of electroactive and photoactive rod-coil copolymers have been designed, synthesized, and investigated to explore a new structural motif for organizing molecular and macromolecular materials at the supramolecular structure level for enhanced functional and solid state photophysical properties. The rod-coil copolymers consisting of electroactive and photoactive rodlike conjugated segments and inactive coillike segments, exemplified by poly(1,4-phenylenebenzobisthiazole-co-decamethylenebenzobisthiazole) and poly((1,4-phenylenedivinylene)benzobisthiazole-co-decamethylenebenzobisthiazole), have semiflexible (semirigid) chains whose flexibility (rigidity), folding, intermolecular interactions, and packing, and hence the solid state supramolecular structure and photophysical properties of the materials, are regulated by copolymer composition. The molecular structure, chain sequence lengths, and copolymer composition were determined by NMR (H-1, C-13), FTIR, and W-vis spectra. The sequence length distribution of the conjugated rodlike segments predicted from the copolymerization statistics was in good agreement with the H-1 NMR results. It is shown that nanocomposites are formed at rod molar fractions of less than 0.5 which also marks a dramatic change in the photophysical properties of the copolymers. The photoluminescence quantum yield varied with copolymer composition, reaching over 6- and 7-fold enhancements compared to the ''bulk'' pure conjugated polymers. The photoluminescence peak of the rod-coil copolymers varied from 486 to 640 nm which represents emission colors that span the visible (blue to red) region.