title: Light-harvesting action spectroscopy of single conjugated polymer nanowires.
abstract: We study exciton migration in single molecular nanowires, dye-endcapped multichromophoric conjugated polymers, as a function of excitation energy. This approach reveals the actual molecular absorption properties, uncovering the molecules within an ensemble and the chromophores within a molecule which contribute to absorption at a given wavelength. As the excitation energy is raised, an increasing number of polymers exhibit energy transfer suggesting that, in contrast to the emission spectrum, the absorption of a single chain under energy transfer conditions can be very broad even at 5 K. At the same time, the polarization anisotropy in excitation decreases due to an increase in the number of noncolinear chromophores involved in absorption. Power and wavelength-dependent measurements clearly discern the exciton blockade effect that gives rise to strong fluctuations of energy transfer. Although the polymer and endcap constitute nominally discrete spectroscopic entities, we are able to identify a subtle influence of the primary backbone exciton energy on the ultimate endcap emission. This demonstration of interchromophoric cooperativity provides a direct realization of how nonradiative energy dissipation in one nanoscale unit influences the spectroscopy of another.
authors.affiliation: Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Manfred J
authors.initials: MJ
authors.lastname: Walter
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Borys
authors.forename: Kipp J
authors.initials: KJ
authors.lastname: van Schooten
authors.forename: John M
authors.initials: JM
authors.lastname: Lupton
mesh_terms: D016880:Anisotropy; D004735:Energy Transfer; D008027:Light; D008956:Models, Chemical; D036103:Nanotechnology / Q000379:methods; D053770:Nanowires / Q000737:chemistry*; D016011:Normal Distribution; D010777:Photochemistry / Q000379:methods; D011108:Polymers / Q000737:chemistry*; D012542:Scattering, Radiation; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature
chemical_list: D011108:Polymers