title: Quenching of the perylene fluorophore by stable nitroxide radical-containing macromolecules.
abstract: Stable nitroxide radical bearing organic polymer materials are attracting much attention for their application as next generation energy storage materials. A greater understanding of the inherent charge transfer mechanisms in such systems will ultimately be paramount to further advancements in the understanding of both intrafilm and interfacial ion- and electron-transfer reactions. This work is focused on advancing the fundamental understanding of these dynamic charge transfer properties by exploiting the fact that these species are efficient fluorescence quenchers. We systematically incorporated fluorescent perylene dyes into solutions containing the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radical and controlled their interaction by binding the TEMPO moiety into macromolecules with varying morphologies (e.g., chain length, density of radical pendant groups). In the case of the model compound, 4-oxo-TEMPO, quenching of the perylene excited state was found to be dominated by a dynamic (collisional) process, with a contribution from an apparent static process that is described by an ∼2 nm quenching sphere of action. When we incorporated the TEMPO unit into a macromolecule, the quenching behavior was altered significantly. The results can be described by using two models: (A) a collisional quenching process that becomes less efficient, presumably due to a reduction in the diffusion constant of the quenching entity, with a quenching sphere of action similar to 4-oxo-TEMPO or (B) a collisional quenching process that becomes more efficient as the radius of interaction grows larger with increasing oligomer length. This is the first study that definitively illustrates that fluorophore quenching by a polymer system cannot be explained using merely a classical Stern-Volmer approach but rather necessitates a more complex model.
authors.affiliation: Chemical and Materials Science Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States.
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Hughes
authors.forename: Wade A
authors.initials: WA
authors.lastname: Braunecker
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Ferguson
authors.forename: Travis W
authors.initials: TW
authors.lastname: Kemper
authors.forename: Ross E
authors.initials: RE
authors.lastname: Larsen
authors.forename: Thomas
authors.initials: T
authors.lastname: Gennett
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D009589:Nitrogen Oxides / Q000737:chemistry*; D010569:Perylene / Q000737:chemistry*; D010880:Piperidines / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D003497:Cyclic N-Oxides; D005456:Fluorescent Dyes; D009589:Nitrogen Oxides; D010880:Piperidines; D011108:Polymers; D010569:Perylene; C032727:piperidine; C039900:nitroxyl; C003959:TEMPO