Ru(bpy)32+ derivatized polystyrenes constructed by nitroxide-mediated radical polymerization. Relationship between polymer chain length, structure and photophysical properties

Abstract

A series of polystyrene-based light harvesting polymers featuring pendant polypyridyl ruthenium complexes has been synthesized. The polymer backbones were prepared by nitroxide-mediated radical polymerization with a variable average molecular weight (M_n) ranging from ∼5500 to ∼24 000 g mol⁻¹. Pendant Ru(II) polypyridyl complexes were grafted to the polymer backbone by azide–alkyne click chemistry to afford chromophore loaded polymers. The resulting polystyrene-based polychromophores with pendant Ru(II) polypyridyl complexes (PS-Ru) were characterized by nuclear magnetic resonance and infrared spectroscopy, confirming the high efficiency of the click grafting. The photophysical and electrochemical properties of the series of PS-Ru polymers were characterized in solution and investigated as a function of polymer chain length and solvent. The electrochemical properties of PS-Ru maintained the characteristics of the individual Ru(II) polypyridyl units. Emission quantum yield and lifetime studies reveal that the metal-to-ligand charge transfer (MLCT) excited states are quenched to a variable extent depending on the molecular weight of the polymers, consistent with intramolecular energy transfer and self-quenching in polymers with longer chain lengths. To support the synthetic effort, molecular dynamics simulations of the polypyridyl ruthenium derivatized polystyrenes in different solvents were conducted.