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Photoluminescence and micro-patterning of the star-shaped truxene-core oligofluorenes

Photoluminescence and micro-patterning of the star-shaped truxene-core oligofluorenes. Min Wu , D. Elfstrom, B. Guilhabert, E. Gu and M.D. Dawson Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, UK P. J. Skabara and A. L. Kanibolotsky

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Photoluminescence and micro-patterning of the star-shaped truxene-core oligofluorenes

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  1. Photoluminescence and micro-patterning of the star-shaped truxene-core oligofluorenes Min Wu, D. Elfstrom, B. Guilhabert, E. Gu and M.D. Dawson Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, UK P. J. Skabara and A. L. Kanibolotsky Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL A.R. Mackintosh and R.A. Pethrick Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL

  2. Outline • The truxene-core oligofluorenes (T1-T4) • Deep UV transparent photo-curable polymers • Oligomer/divinyl polymer blends • Laser direct writing in truxene blends • Photoluminescence study of truxene blends • Conclusions and perspective ©The Institute of Photonics, University of Strathclyde 2007

  3. The truxene-core oligofluorenes (T1-T4) • Instead of increasing the arm size by repetitive addition of arm units to the star-shaped oligomer through Suzuki coupling, P.J.Skabara et al. attached oligofluorene arms of corresponding length directly to the central truxene core • This results in highly soluble, intrinsically two-dimensional nanosized macromolecules T1-T4. Ref: A.L. Kanibolotsy et al., J.AM.CHEM.SOC, 2004, 126, 13695-13702 ©The Institute of Photonics, University of Strathclyde 2007

  4. Excellent properties of T1-T4 • High thermal stability with no decomposition below 400°C • Good electrochemical stability towards both p- and n-doping • Bright blue-violet emission wavelength around 400-420nm with quantum efficiencies of ~50-60% in the solid state • Excellent film-forming properties (e.g. 230nm thickness for spin-coated T1 film) and nanoscale size of macromolecules (1.7 x 7nm for T4) Ref: A.L. Kanibolotsy et al., J.AM.CHEM.SOC, 2004,126, 13695-13702 ©The Institute of Photonics, University of Strathclyde 2007

  5. Photoluminescence study of T1-T4 Summary of PL spectrum data • Photoluminescence study shows the excellent environmental stability of T1-T4 Spectra measured 9 days later ©The Institute of Photonics, University of Strathclyde 2007

  6. Deep UV transparent photo-curable polymers The photo-curable polymers are developed by R.A. Pethricket al. in the Chemistry department, University of Strathclyde. This polymer is ~100% transparent even at deep UV wavelength <300nm. Monomer 1,4-Cyclohexanedimethanol divinyl ether (CHDV) Photo acid generator lipophilic iodonium based PAG: p-(octaneoxyphenyl)phenyl iodonium hexanefluoro antimonate ©The Institute of Photonics, University of Strathclyde 2007

  7. The oligomer/ divinyl polymer blends • Advantages of blending truxene oligomers with divinyl polymers: • - The blend solution doesn’t affect the luminescence property of the pure materials (as shown through the photoluminescence study) • - The blend solution can be locally photo-cured allowing ‘direct write’ patterning • - The blend solution improves the processability of the pure truxene oligomers • Photoluminescence studies show the Truxene blends have similar luminescence properties to pure Truxene oligomers ©The Institute of Photonics, University of Strathclyde 2007

  8. Photocure mechanism for the Truxene blends The absorption spectrum of the photo acid generator and the truxene oligomers are shown below. We firstly observed that the energy transfer appeared between the light emitting polymers and photo acid generator during the curing (Ref 2). However the details are still under investigation. Ref: 1. A.L. Kanibolotsy et al., J.AM.CHEM.SOC, 2004,126, 13695 2. E.Gu et al. Appl. Phys. Lett.90,031116(2007) ©The Institute of Photonics, University of Strathclyde 2007

  9. Excellent Patterning method: laser direct writing Camera UV (374 nm) laser Shutter Sample stage • Laser direct writing (LDW) is an attractive approach to micro and nano-patterning due to its simplicity and flexibility. ©The Institute of Photonics, University of Strathclyde 2007

  10. Laser direct writing: experimental set-up • A diode laser operating at 374nm • A variable neutral density filter wheel to attenuate the intensity and thus control the exposure. • A mechanical shutter, with a minimum open time of 10ms. • A beam expander to make sure the back aperture of the objective is filled. • An objective, N.A. = 0.4 and 20x magnification, to focus the laser beam on to the sample. • An XY translation stage, with a resolution of 1μm and a maximum speed of 1.5mm/s. • A CCD camera and UV-filtered white light illumination to image the sample. • A computer to control the shutter and the stages. ©The Institute of Photonics, University of Strathclyde 2007

  11. The laser direct writing (LDW) process clean the substrate Apply polymer to substrate Writing by moving the sample Developing (If needed) Microstructure formation Post-cure or post-bake ©The Institute of Photonics, University of Strathclyde 2007

  12. Truxene oligomer blend microstructures 285uW~ 3.3uW 10ms exposure 3.3uW 1s~10ms exposure 3.3uW 1mm/s scanning speed Truxene/ Divinyl= 1:3 V% Normal illumination UV (lamp) illumination 285uW~ 3.3uW 10ms exposure 3.3uW 1s~10ms exposure 3.3uW 1mm/s scanning speed 5.5uW 1mm/s scanning speed 100um 100um Truxene/ Divinyl= 1:10 V% 100um 100um ©The Institute of Photonics, University of Strathclyde 2007

  13. Truxene blend microstructure profiles 50µm 50µm Truxene/ Divinyl= 1:3 Volume% The feature sizes of the micro spots vary from 12µm to 39µm in diameter. Feature Size Width Height 19 µm 28µm 13 µm 23µm ©The Institute of Photonics, University of Strathclyde 2007

  14. LDW parameter effects on microstructure feature size Parameters for Truxene T3/ divinyl polymer blends (1:3 V%) ©The Institute of Photonics, University of Strathclyde 2007

  15. Photoluminescence study for truxene blend microstructures #1 PL spectra of truxene blend microstructures under different fluence of laser spot ©The Institute of Photonics, University of Strathclyde 2007

  16. Photoluminescence study for truxene blends microstructures #2 Different concentration in vinyl polymers under same writing parameters. (Power: 62µW, Writing speed: 1mm/s) Normal illumination 100µm 100µm UV illumination Truxene:vinyl = 1:3 (V%) Truxene:vinyl = 1:10 (V%) ©The Institute of Photonics, University of Strathclyde 2007

  17. Conclusions and perspective • Soluble star-shaped oligofluorenes (T1-T4) based on a truxene-core have been synthesized • Truxene oligomers have good thermal, electrochemical and environmental stability, high photoluminescence efficiency, excellent blendability and processing properties. • Truxene oligomer/divinyl polymer blend microstructures have been fabricated by laser direct writing with feature size ~10µm • Photoluminescence studies show the stability of the truxene oligomer blends under different laser dose and blend concentrations • With the novel properties demonstrated above, the Truxene oligofluorene blends are attractive candidates for organic optoelectronic device fabrication ©The Institute of Photonics, University of Strathclyde 2007

  18. Acknowledgements This work was supported under: EPSRC Science & Innovation Award on ‘Molecular Nanometrology’ (EP/D062861/1) and RCUK Basic Technology Award on ‘A Thousand Micro-emitters…’ (GR/S/85764/1) ©The Institute of Photonics, University of Strathclyde 2007

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