TY  - JOUR
A1  - Zhang, Ning
A1  - Hayer, Anna
A1  - Al-Suti, Mohammed K.
A1  - Al-Belushi, Rayya A.
A1  - Khan, Muhammad S.
A1  - Köhler, Anna
T1  - The effect of delocalization on the exchange energy in meta- and para-linked Pt-containing carbazole polymers and monomers
N2  - A series of novel platinum-containing carbazole monomers and polymers was synthesized and fully characterized by UV-VIS absorption, luminescence, and photoinduced absorption studies. In these compounds, a carbazole unit is incorporated into the main chain via either a para- or a meta-linkage. We discuss the effects of linkage and polymerization on the energy levels of S-1, T-1, and T-n. The S-1-T-1 splitting observed for the meta-linked monomer (0.4 eV) is only half of that in the para-linked monomer (0.8 eV). Upon polymerization, the exchange energy in the para- linked compound reduces, yet still remains larger than in the meta-linked polymer. We attribute the difference in exchange energy to the difference in wave function overlap between electron and hole in these compounds. (c) 2006 American Institute of Physics
Y1  - 2006
UR  - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=JCPSA6000124000024244701000001&idtype=cvips&doi=10.1063/1.2200351&prog=normal
U6  - https://doi.org/10.1063/1.2200351
ER  - 
TY  - JOUR
A1  - Hayer, Anna
A1  - de Halleux, Veronique
A1  - Köhler, Anna
A1  - El-Garoughy, Abdel
A1  - Meijer, E. W.
A1  - Barbera, Joaquin
A1  - Tant, Julien
A1  - Levin, Jeremy
A1  - Lehmann, Matthias
A1  - Gierschner, Johannes
A1  - Cornil, Jerome
A1  - Geerts, Yves Henri
T1  - Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures
N2  - 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
Y1  - 2006
UR  - http://pubs.acs.org/journal/jpcbfk
U6  - https://doi.org/10.1021/Jp0573689
SN  - 1520-6106
ER  - 
TY  - JOUR
A1  - Evans, Nicholas R.
A1  - Devi, Lekshmi Sudha
A1  - Mak, Chris S. K.
A1  - Watkins, Scott E.
A1  - Pascu, Sofia I.
A1  - Köhler, Anna
A1  - Friend, Richard H.
A1  - Williams, Charlotte K.
A1  - Holmes, Andrew B.
T1  - Triplet energy back transfer in conjugated polymers with pendant phosphorescent iridium complexes
N2  - The nature of Dexter triplet energy transfer between bonded systems of a red phosphorescent iridium complex 13 and a conjugated polymer, polyfluorene, has been investigated in electrophosphorescent organic light-emitting diodes. Red- emitting phosphorescent iridium complexes based on the [Ir(btp)2(acac)]fragment (where btp is 2-(2 '- benzo[b]thienyl)pyridinato and acac is acetylacetonate) have been attached either directly (spacerless) or through a - (CH2)(8)-chain (octamethylene-tethered) at the 9-position of a 9-octylfluorene host. The resulting dibromo- functionalized spacerless (8) or octamethylene-tethered (12) fluorene monomers were chain extended by Suzuki polycondensations using the bis(boronate)-terminated fluorene macromonomers 16 in the presence of end-capping chlorobenzene solvent to produce the statistical spacerless (17) and octamethylene-tethered ( 18) copolymers containing an even dispersion of the pendant phosphorescent fragments. The spacerless monomer 12 adopts a face-to-face conformation with a separation of only 3.6 angstrom between the iridium complex and fluorenyl group, as shown by X-ray analysis of a single crystal, and this facilitates intramolecular triplet energy transfer in the spacerless copolymers 17. The photo- and electroluminescence efficiencies of the octamethylene-tethered copolymers 18 are double those of the spacerless copolymers 17, and this is consistent with suppression of the back transfer of triplets from the red phosphorescent iridium complex to the polyfluorene backbone in 18. The incorporation of a -(CH2)(8)- chain between the polymer host and phosphorescent guest is thus an important design principle for achieving higher efficiencies in those electrophosphorescent organic light-emitting diodes for which the triplet energy levels of the host and guest are similar
Y1  - 2006
UR  - http://pubs.acs.org/journal/jacsat
U6  - https://doi.org/10.1021/Ja0584267
SN  - 0002-7863
ER  -