Polarised emission from individual self-assembled  -conjugated nanofibres on a solid support

1. Polarised emission from individual self-assembled -conjugated nanofibres on a solid support Frans J.P. Wijnen, Jeroen C. Gielen, Cécile R.L.P.N. Jeukens, Peter C.M. Christianen and J.C. Maan High Field Magnet Laboratory, Radboud University Nijmegen Pascal Jonkheijm, Albert P.H.J. Schenning and E.W. Meijer, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology

2. Introduction • Determine order of functional nanofibres polymers / anorganic / carbon nanotube / molecular self-assembly Self-assembled molecular structures • Molecules with non-covalent interactions: self-organisation into superstructures. • Spontaneous assembly process • Building block  superstructure • Versatile (emission, conductivity) Outline • Self-assembled OPV nanofibres • Characterisation: polarised fluorescence microscopy • Dipole model, analyse FM results, determine order Polarised emission from individual self-assembled π-conjugated nanofibres on a support

3. From OPV molecules to fibre Tetra(p-phenylenevinylene) molecule: JACS 123, 409 (2001) & JACS 125, 15941 (2003) Polarised emission from individual self-assembled π-conjugated nanofibres on a support

4. Transfer to Graphite • AFM shows individual fibres length: several microns; height: 5 nm 5 nm Polarised emission from individual self-assembled π-conjugated nanofibres on a support

5. Fluorescence Microscope setup • Polarised imaging of individual nanofibres To detector: Intensified CCD camera or monochromator Incoming beam: Argon laser @ 457.9 nm Polarised emission from individual self-assembled π-conjugated nanofibres on a support

6. Emission spectrum single fibre Spectrum: single nanofibre on graphite similar to OPV-solution Polarised emission from individual self-assembled π-conjugated nanofibres on a support

7. Polarised images Excitation:  Detection:  Excitation:  Detection:  1 μm 1 μm + = Polarised emission from individual self-assembled π-conjugated nanofibres on a support

8. Colour coded polarisation ratio • Dipole moment lies in plane of the OPV molecule. • Polarisation direction determined by nanofibre orientation Polarised emission from individual self-assembled π-conjugated nanofibres on a support

9. Polarised nanofibres Combined I and I images into colour coded image: • Observed profound polarisation • Polarisation is homogeneous over entire fibre • Ratio (R= I / I ) depends on fibre orientation JACS 127, 2080 (2005) Polarised emission from individual self-assembled π-conjugated nanofibres on a support

10. Results • Polarisation ratio only 2: Why? Polarised emission from individual self-assembled π-conjugated nanofibres on a support

11. Model a nanofibre • Angle between consecutive dimers: 12º  15 molecules sufficient to model fibre • Represent molecule by dipole • Substrate: graphite Polarised emission from individual self-assembled π-conjugated nanofibres on a support

12. Depolarising effects • Disorder?? (requires unrealistic angles) • Helicity of the fibres (z-dipole is unpolarised) • The numerical aperture of the objective • Dielectric properties of the supporting substrate Free dipole Dipole on graphite red arrow: x- or y-dipole blue arrow: z-dipole Polarised emission from individual self-assembled π-conjugated nanofibres on a support

13. Polarisation ratio explained! • Data fits calculation  highly ordered nanofibres Polarised emission from individual self-assembled π-conjugated nanofibres on a support

14. Conclusions & Outlook Conclusions: • Self-assembled, highly ordered nanofibres • Profound homogeneous polarisation • Polarisation ration depends on substrate Outlook: • Look into exciton effects • Other (smarter) substrates Polarised emission from individual self-assembled π-conjugated nanofibres on a support