@article{DeviAlSutiDoscheetal.2008,
  author    = {Devi, Lekshmi Sudha and Al-Suti, Mohammed K. and Dosche, Carsten and Khan, Muhammad S. and Friend, Richard H. and K{\"o}hler, Anna},
  title     = {Triplet energy transfer in conjugated polymers : I. Experimental investigation of a weakly disordered compound},
  year      = {2008},
  abstract  = {Efficient triplet exciton emission has allowed improved operation of organic light-emitting diodes (LEDs). To enhance the device performance, it is necessary to understand what governs the motion of triplet excitons through the organic semiconductor. Here, we have investigated triplet diffusion using a model compound that has weak energetic disorder. The Dexter-type triplet energy transfer is found to be thermally activated down to a transition temperature T- T, below which the transfer rate is only weakly temperature dependent. We show that above the transition temperature, Dexter energy transfer can be described within the framework of Marcus theory. We suggest that below T-T, the nature of the transfer changes from phonon-assisted hopping to quantum-mechanical tunneling. The lower electron-phonon coupling and higher electronic coupling in the polymer compared to the monomer results in an enhanced triplet diffusion rate.},
  language  = {en}
}
@article{ParkinsonAharonChangetal.2007,
  author    = {Parkinson, P. and Aharon, E. and Chang, M. H. and Dosche, Carsten and Frey, G. L. and K{\"o}hler, Anna and Herz, L. M.},
  title     = {Dimensionality-dependent energy transfer in polymer-intercalated SnS2 nanocomposites},
  doi       = {10.1103/Physrevb.75.165206},
  year      = {2007},
  abstract  = {We have investigated the influence of dimensionality on the excitation-transfer dynamics in a conjugated polymer blend. Using time-resolved photoluminescence spectroscopy, we have measured the transfer transients for both a three-dimensional blend film and for quasi-two-dimensional monolayers formed through intercalation of the polymer blend between the crystal planes of an inorganic SnS2 matrix. We compare the experimental data with a simple, dimensionality- dependent model based on electronic coupling between electronic transition moments taken to be point dipoles. Within this approximation, the energy-transfer dynamics is found to adopt a three-dimensional character in the solid film and a two-dimensional nature in the monolayers present in the SnS2-polymer nanocomposite.},
  language  = {en}
}
@article{HayerdeHalleuxKoehleretal.2006,
  author    = {Hayer, Anna and de Halleux, Veronique and K{\"o}hler, Anna and El-Garoughy, Abdel and Meijer, E. W. and Barbera, Joaquin and Tant, Julien and Levin, Jeremy and Lehmann, Matthias and Gierschner, Johannes and Cornil, Jerome and Geerts, Yves Henri},
  title     = {Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures},
  issn      = {1520-6106},
  doi       = {10.1021/Jp0573689},
  year      = {2006},
  abstract  = {A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The therniotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70\% in dichloromethane solution and 62\% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition},
  language  = {en}
}