Correlating Pyrene Excimer Formation with Polymer Chain Dynamics in Solution. Possibilities and Limitations

• Published in: Macromolecules 2007-09, Vol.40 (18), p.6647-6657
• Main Authors: Ingratta, Mark, Duhamel, Jean
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma070368h

Four types of pyrene-labeled polystyrene samples (Py−PS) were prepared and the process of excimer formation between the pyrene labels was characterized by steady-state and time-resolved fluorescence to assess the effect the mode of pyrene incorporation into a polymer has on the kinetics of excimer formation. The pyrene label was incorporated into the PS backbone by either (1) reacting 1-pyrenemethoxide with a chloromethylated polystyrene backbone to yield the GrE−PS series, (2) copolymerizing styrene with 4-(1-pyrenyl)methoxymethylstyrene to yield the CoE−PS series, (3) copolymerizing styrene with N-(1-pyrenylmethyl)acrylamide to yield the CoA−PS series, or (4) polymerizing α,ω-dicarboxyl end-capped polystyrenes with l-lysine-1-pyrenemethylamide dihydrochloride to yield the ES−PS series. Steady-state and time-resolved fluorescence experiments demonstrated that the long and flexible linker of GrE−PS and CoE−PS enabled more efficient excimer formation than the short and rigid linker of CoA−PS, and that spacing the pyrene pendants in ES−PS led to a strong reduction in excimer formation. The fluorescence blob model (FBM) was applied to analyze quantitatively the monomer and excimer fluorescence decays of the four Py−PSs. The FBM analysis confirmed that the longer ether linker of GrE−PS and CoE−PS enabled the excited pyrene label to probe a larger volume inside the polymer coil. The level of clustering of the pyrene pendants was found to be minimal for ES−PS, as expected from its structural design. Interestingly, the pyrene pendants were twice more clustered for GrE−PS than for CoE−PS, despite both polymers having an identical chemical structure. The results for the GrE−PS and CoE−PS series suggest that reacting groups distribute themselves differently in a copolymer whether they are incorporated by a grafting onto reaction or copolymerization.