Ligand Exchange Reaction for Controlling the Conformation of Platinum-Containing Polymers

Control of the conformation of polymers can be achieved by the ligand exchange reaction of optically active poly(phenyleneethynylene) 1′ containing −Pt(PPh3)2– moieties in the main chain. Polymer 1′ was reacted with 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), and 1,4-bis(diphenylphosphino)butane (dppb) to give the corresponding polymers 2′, 3′, and 4′ containing −Pt(dppe)–, −Pt(dppp)– , and −Pt(dppb)– moieties in the main chain, respectively. Polymers 1′ and 2′ exhibited negligibly small circular dichroism (CD) signals in THF, indicating the absence of regulated chiral structures, while polymers 3′ and 4′ exhibited strong CD signals in THF. The dynamic light scattering (DLS) analysis of the polymer solutions indicated that polymer 3′ formed a chirally regulated one-handed helix intramolecularly bridged with dppp, and polymer 4′ formed aggregates intramolecularly and/or intermolecularly bridged with dppb.