Polarization anisotropy dynamics for thin films of a conjugated polymer aligned by nanoimprinting

Time-integrated and femtosecond time-resolved photoluminescence spectroscopy has been used to study the dynamic emission polarization anisotropy for thin films of a conjugated polymer whose chains had been aligned through a nanoimprinting technique. The results indicate a high degree of chain alignment, with the presence of a small fraction of unaligned chain domains in film regions far from the imprinted surface. The time-averaged emission from aligned domains is found to be slightly shifted to higher photon energies compared to that from more disordered film regions. This effect is attributed to a subtly different chain packing geometry in the more aligned regions of the film, which leads to a reduced exciton diffusivity and inhibits energetic relaxation of the exciton in the inhomogeneously broadened density of states. While for an unaligned reference film, exciton migration results in a nearly complete depolarization of the emission over the first 300 ps, for the aligned films, interchain exciton hopping from unaligned to aligned domains is found to increase the anisotropy over the same time scale. In addition, excitons generated in aligned film domains were found to be slightly more susceptible to nonradiative quenching effects than those in disordered regions deeper inside the film, suggesting a marginally higher defect density near the nanoimprinted surface of the aligned film.

[1]  R. Friend,et al.  Uniaxial alignment of liquid-crystalline conjugated polymers by nanoconfinement. , 2007, Nano letters.

[2]  Daniel Moses,et al.  Anisotropic photoluminescence properties of oriented poly( p -phenylene-vinylene) films: Effects of dispersion of optical constants , 2007 .

[3]  V. Dravid,et al.  Effect of spatial confinement on the glass-transition temperature of patterned polymer nanostructures. , 2007, Nano letters.

[4]  L. Herz,et al.  Intermolecular interaction effects on the ultrafast depolarization of the optical emission from conjugated polymers. , 2007, Physical review letters.

[5]  Photoexcitation dynamics in thin films of insulated molecular wires , 2006 .

[6]  R. Friend,et al.  Anisotropic optical properties in electroluminescent conjugated polymers based on grazing angle photoluminescence measurements. , 2006, The Journal of chemical physics.

[7]  R. T. Phillips,et al.  Influence of copolymer interface orientation on the optical emission of polymeric semiconductor heterojunctions. , 2006, Physical review letters.

[8]  Excellent uniaxial alignment of poly(9,9-dioctylfluorenyl-2,7-diyl) induced by photoaligned polyimide films , 2005 .

[9]  G. R. Webster,et al.  Ultrafast depolarization of the fluorescence in a conjugated polymer , 2005 .

[10]  H. Sirringhaus,et al.  Effects of packing structure on the optoelectronic and charge transport properties in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole). , 2005, Journal of the American Chemical Society.

[11]  Richard H. Friend,et al.  Spin-cast thin semiconducting polymer interlayer for improving device efficiency of polymer light-emitting diodes , 2005 .

[12]  Richard H. Friend,et al.  General observation of n-type field-effect behaviour in organic semiconductors , 2005, Nature.

[13]  Carlos Silva,et al.  Time-dependent energy transfer rates in a conjugated polymer guest-host system , 2004 .

[14]  J. Mikroyannidis,et al.  Synthesis, characterization and photophysics of poly(p-phenylenevinylene)-type polymers bearing substituted 2H-imidazole rings in the backbone , 2004 .

[15]  S. Jenekhe,et al.  Synthesis, Photophysics, and Electroluminescence of Conjugated Poly(p-phenylenevinylene) Derivatives with 1,3,4-Oxadiazoles in the Backbone , 2003 .

[16]  V. Sundström,et al.  Ultrafast Excitation Transfer and Trapping in a Thin Polymer Film. , 2003 .

[17]  David Beljonne,et al.  Electronic and optical properties of polyfluorene and fluorene-based copolymers: A quantum-chemical characterization , 2003 .

[18]  D. Bradley,et al.  Raman Anisotropy Measurements: An Effective Probe of Molecular Orientation in Conjugated Polymer Thin Films , 2003 .

[19]  Richard H. Friend,et al.  Vertically segregated polymer-blend photovoltaic thin-film structures through surface-mediated solution processing , 2002 .

[20]  Donal D. C. Bradley,et al.  Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase , 2000 .

[21]  R. T. Phillips,et al.  Effects of interchain interactions, polarization anisotropy, and photo-oxidation on the ultrafast photoluminescence decay from a polyfluorene , 2000 .

[22]  Franco Cacialli,et al.  Molecular-scale interface engineering for polymer light-emitting diodes , 2000, Nature.

[23]  Ignacio B. Martini,et al.  Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton-Exciton Annihilation and Aggregation in MEH-PPV Films , 2000 .

[24]  E. W. Meijer,et al.  Two-dimensional charge transport in self-organized, high-mobility conjugated polymers , 1999, Nature.

[25]  Donal D. C. Bradley,et al.  MONODOMAIN ALIGNMENT OF THERMOTROPIC FLUORENE COPOLYMERS , 1999 .

[26]  Akio Yasuda,et al.  Blue Polarized Electroluminescence from a Liquid Crystalline Polyfluorene , 1999 .

[27]  Yong Cao,et al.  Improved quantum efficiency for electroluminescence in semiconducting polymers , 1999, Nature.

[28]  J. C. Scott,et al.  Electrical and Photoinduced Degradation of Polyfluorene Based Films and Light-Emitting Devices , 1999 .

[29]  V. Sundström,et al.  Energy transfer in a conjugated polymer with reduced inter-chain coupling , 1998 .

[30]  R. T. Phillips,et al.  Polarization dependence of the ultrafast photoluminescence of oriented poly(p-phenylenevinylene) , 1997 .

[31]  Samuel,et al.  Exciton dynamics in electroluminescent polymers studied by femtosecond time-resolved photoluminescence spectroscopy. , 1995, Physical review. B, Condensed matter.

[32]  C. A. Walsh,et al.  Efficient photodiodes from interpenetrating polymer networks , 1995, Nature.

[33]  Miller,et al.  Defect quenching of conjugated polymer luminescence. , 1994, Physical review letters.

[34]  Kurz,et al.  Femtosecond energy relaxation in pi -conjugated polymers. , 1993, Physical review letters.

[35]  R. N. Marks,et al.  Light-emitting diodes based on conjugated polymers , 1990, Nature.

[36]  D. Bradley.  Precursor-route poly(p-phenylenevinylene): polymer characterisation and control of electronic properties , 1987 .