The Synthesis and Characterization of Energy-Conducting Polymers with Pendant Inorganic Chromophores
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EE8.10.1
The Synthesis and Characterization of Energy-Conducting Polymers with Pendant Inorganic Chromophores
James H. Alstrum-Acevedo, Joseph M. DeSimone, C. K. Schauer, and John M. Papanikolas* University of North Carolina, Department of Chemistry Chapel Hill, NC 27599-3290 ABSTRACT We are interested in the synthesis, characterization, and performance evaluation of functional nanoscale materials comprised of a polymeric scaffold with appended cationic transition-metal lumiphores. We have developed a methodology to prepare, spectroscopically characterize, and evaluate a series of organic copolymers functionalized with inorganic chromophores. Preparation of these hybrid systems first involves the synthesis of a linear AB diblock copolymeric scaffold in which A is polystyrene (PS) and B is poly(p-tertbutoxycarbonyloxystyrene) (PStBOC), using Reversible Addition-Fragmentation chain-Transfer (RAFT) radical polymerization. The PStBOC block (B) was converted into poly(4hydroxystyrene) by acid hydrolysis of the t-BOC moieties, and Ru(II) trisbipyridyl complexes were covalently appended using standard ester coupling reagents. These lumiphores were selected due to their strong absorbance in the visible spectrum, chemical/photochemical stability, useful redox properties, and long-lived excited state lifetimes. Attachment of the cationic transition-metal chromophores to block B of these linear AB diblock copolymeric arrays is expected to promote solid-state self-assembly into nanoscale structures. The metal-loaded macromolecular assemblies were characterized spectroscopically and the determination of the solid-state morphology of films of these materials was investigated using Transmission Electron Microscopy (TEM).
INTRODUCTION We have been interested in the synthesis, characterization, and performance evaluation of homopolymeric arrays composed of polystyrene (PS) scaffolding appropriately derivatized to covalently attach transition metal chromophores via an amide or ester bond [1-7]. These polymeric arrays were fully loaded with Ru(II) and/or Os(II) trisbipyridyl complexes. These lumiphores were selected due to their strong absorbance in the visible spectrum, chemical/photochemical stability, useful redox properties, and long-lived excited state lifetimes. The evaluated materials, consisted of 20 repeat units loaded with 17 Ru(II) and 3 Os(II) chromophores on average, exhibited excellent performance with respect to the rapid efficient (99.7-99.9%) sensitization of pendant Os(II) complexes [7]. The first generation materials, do not exhibit directed spatial control of energy transfer processes. This is a result of the random loading of the lumiphores onto the polymer backbone. The use of diblock copolymers provides a possible route to obtain directed spatial control of energy transfer, especially if the absorbent/luminescent blocks are concentrated within ordered microstructures. Our current efforts have focused on the synthesis of linear styrenic AB diblock copolymer arrays capable of self-assembly into microstructures
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