Triplet Energy Transport in Platinum-Acetylide Light Harvesting Arrays

Light harvesting and triplet energy transport is investigated in chromophore-functionalized polystyrene polymers featuring light harvesting and energy acceptor chromophores (traps) at varying loading. The series of precision polymers was constructed via reversible addition fragmentation transfer polymerization and functionalized with platinum acetylide triplet chromophores by using an azide-alkyne click reaction. The polymers have narrow polydispersity and degree of polymerization similar to 60. The chromophores have the general structure, trans-[-R-C6H4 C C-Pt(PBu3)(2)-C C-Ar], where R is the attachment point to the polystyrene backbone and Ar is either -C6H4-C C-Ph or -pyrenyl (PE2-Pt and Py-Pt, respectively, with triplet energies of 2.35 and 1.88 eV). The polychromophores contain mainly the high-energy PE2-Pt units (light absorber and energy donor), with randomly distributed Py-Pt units (3-20% loading, energy acceptor). Photophysical methods are used to study the dynamics and efficiency of energy transport from the PE2-Pt to Py-Pt units in the polychromophores. The energy transfer efficiency is >90% for copolymers that contain 5% of the Py-Pt acceptor units. Time-resolved phosphorescence measurements combined with Monte Carlo exciton dynamics simulations suggest that the mechanism of exciton transport is exchange energy transfer hopping between PE2-Pt units.