Solution Self-Assembly and Photophysics of Platinum Complexes Containing Amphiphilic Triblock Random Copolymers Prepared by ROMP

Ring-opening metathesis polymerization was used to synthesize amphiphilic, phosphorescent block copolymers that self-assemble into nanometer-scaled aggregates when dissolved in a selective solvent. The triblock random copolymer architecture is built up by using an oligoglycol-substituted norbornene derivative for the hydrophilic part, 2,3-norbomenedicarboxylic acid dimethyl ester, as the first segment of the hydrophobic part and a statistical segment made using norbomene-functionalized dyes as the second segment of the hydrophobic part. The dyes comprise a blue fluorescent carbazole derivative serving as the host and a red phosphorescent platinum complex serving as the guest material. Emission properties of the amphiphilic triblock random copolymer dissolved in a nonselective solvent are exclusively determined by the host material. Only blue emission of the carbazole-derivative can be observed. When the polymer is dissolved in a selective solvent, polymer aggregates are formed and energy transfer occurs. In this case, deep red phosphorescence stemming from the platinum complex used as guest component can be observed. The amphiphilic triblock random copolymer architecture allows for the dispersion of the platinum chromophore in a solvent in which the parent chromophore is insoluble, the realization of a large Stokes, shift of about 260 nun and significant suppression of platinum complex self-quenching, resulting in considerable phosphorescent quantum yields. Absorbance, luminescence, quantum yield, and lifetime measurements of this polymer and several model polymers in selective and unselective solvents as well as in the solid state have been performed to understand the energy transfer from the host to the guest dye in this particular system.