Nano-Assembly of Light Emitting Polymer Films

XiaoTao Hao, David Dunstan

Light emitting polymers are materials that belong to a class of polymers known as conjugated polymers, or also referred to as conducting polymers. These polymers have a backbone of conjugated bonds, which allows the molecules to transfer electrons in a manner similar to a semi-conducting material.

The focus of this project is on fluorescent conjugated polymers, which are conjugated polymers capable of producing fluorescence and electroluminescence. Fluorescent conjugated polymers have a wide range of applications, such as for use in light emitting devices in the form of polymer light emitting diodes or flexible display screens, and in photovoltaic cells. Conjugated polymers have advantages over traditional semi-conducting materials due to ease of processing and desirable mechanical properties of polymers.

It has been proposed that orientation and alignment of polymer molecules will increase the efficiency of fluorescence and improve the performance of devices made from these polymers. Tensile stretching has been identified as a simple and effective method of orienting polymer molecules in a bulk film, therefore experiments on how stretching affects polymer film blends containing fluorescent conjugated polymers were conducted. Single molecule techniques such as Confocal Microscopy and Near-field Scanning Optical Microscopy will be employed to further investigate the underlying photophysics of the conjugated polymers.

The key objectives of this project are to understand the underlying photophysics of single molecules of fluorescent conjugated polymers using single molecule spectroscopy techniques, and to investigate processing methods to achieve light emitting thin films with molecular orientation.

Friction-transfer-FLIM

FLIM-distribution-histogram

(Top) A fluorescence lifetime image of a friction tranferred polymer film.  Here changes in colour represent different fluorescence lifetimes of the polymer.

(Bottom) histogram showing the variation in fluorescence lifetime when the film is cast from a variety of solvents.

Relevant papers:

  • X. Hao, L.J. McKimmie and T.A. Smith, “Spatial Fluorescence Inhomogeneities in Light Emitting Conjugated Polymer Films”, J. Phys. Chem. Lett. 2, 1520–1525 (2011)
  • X. Hao, N.Y. Chan, C. Heck, N. Tanigaki, M.F. Paige, D.E. Dunstan and T.A. Smith, “’Log-Rolling’ Alignment in Friction-Transferred Light-Emitting Conjugated Polymer Thin Films”, Macromolecules, 43(24), 10475-10480, (2010)
  • N.Y. Chan, X. Hao, T.A. Smith and D.E. Dunstan, “Aggregation of Water Soluble Conjugated Polymers in Couette Shear Flow”, J. Phys. Chem. B. 113, 13138–13141, (2009)
  • X. Hao, N.Y. Chan, D.E. Dunstan and T.A. Smith, “Conformational Changes and Photophysical Behavior in Poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] Thin Films Cast under an Electric Field”, J. Phys. Chem. C. 113, 11657–11661 (2009)
  • X. Hao, T. Ryan, M.F. Bailey and T.A. Smith, “Molar Mass Determination of Water-Soluble Light-Emitting Conjugated Polymers by Fluorescence-Based Analytical Ultracentrifugation”, Macromolecules, 42, 2737-2740 (2009)