This paper is focused on how the spectroscopic properties of conjugated polymers evolve in the size range between single polymer chains and the bulk material. The measurements used single-particle spectroscopy techniques and include both static and dynamic measurements. The main observation of this work is that the spectroscopic properties of MEH-PPV evolve rapidly as a function of nanoparticle size and achieve bulk-like properties for nanoparticles greater than 10 nm in size. Nanoparticles were assembled by a reprecipitation technique and characterized by fluorescence emission spectroscopy. The physical origin of the size-dependent spectroscopic properties is assigned to the distance dependence of four main processes: electronic energy transfer between blue and red sites, triplet-triplet annihilation, singlet exciton quenching by triplets, and singlet exciton quenching by hole polarons.

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We perform numerical simulations of purely repulsive soft colloidal particles interacting via a generalized elastic potential and constrained to a two-dimensional plane and to the surface of a spherical shell. For the planar case, we compute the phase diagram in terms of the system's rescaled density and temperature. We find that a large number of ordered phases becomes accessible at low temperatures as the density of the system increases, and we study systematically how structural variety depends on the functional shape of the pair potential. For the spherical case, we revisit the generalized Thomson problem for small numbers of particles N ≤ 12 and identify, enumerate and compare the minimal energy polyhedra established by the location of the particles to those of the corresponding electrostatic system. arXiv:1106.2787v2 [cond-mat.soft]

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Fluorescence emission spectra were recorded for isolated polymer chains of the polyfluorene copolymer, F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)], at 298 and 20 K for two molecular weights (chain lengths). For long-chain F8BT at 298 K, the observed distribution of single-molecule emission maxima G(Emax) is bimodal, with peaks at approximately 2.35 eV ("blue") and approximately 2.25 eV ("red"). Previously, the red forms have been assigned to polymer chains that possess intrachain contacts, which lowers the local singlet exciton energy. At approximately 20 K, G(Emax) collapses into a single broad distribution centered at approximately 2.3 eV for long-chain F8BT. However, this distribution can be further divided into a high-energy edge that is dominated by the "blue" form, while the remainder of the distribution is composed of the "red" form. Low-molecular-weight F8BT samples emit exclusively from the blue form, and no shift in peak maxima with low temperature was observed. A Franck-Condon analysis reveals a decrease in emitting state displacements between spectra measured at 298 and 20 K, suggesting that temperature-induced structural displacements are responsible for the change in the bimodal emission.