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Luminescent metal complexes for optoelectronics based on fluorinated organic ligands

Background

Our aim is to prepare and characterise new materials designed for use in infrared and visible light emitting devices (e.g. optical amplifiers, light emitting diodes, lasers) with efficient transformation of energy. These have potential appications e.g. in improving the efficiency of global telecommunications based on optical fibre be replacing erbium-doped fibre amplifiers. Metal complexes containing highly fluorinated (or chlorinated) ligands have several advantages over their hydrogen-containing counterparts in these appications. The lower vibrational frequency of C–halogen compared with C–H greatly reduces the vibrational quenching of electronically excited lanthanide ions such as Er3+, Nd3+ and Yb3+, thus allowing maximum emission of IR light at useful telecommunications wavelengths, whilst avoiding unwanted heat production[1-3]. Fluoro-organic materials are often relatively volatile and thermally stable, making them suitable for device fabrication by vacuum deposition. Fluorination of aromatic substances can improve their ability to act as electron transport materials and also promote intersystem crossing, thus allowing greater participation by triplet excited states in the photosensitisation process.We have reported the sensitisation of near infrared photoluminescence from Er3+ in complexes with the tetrafluoronitrophenoxide ion [4] and from Yb3+ using the pentafluorotropolonate ion [5]. Recently we have also prepared lanthanide complexes of several fluorinated hydroxyketones [6] which provide particularly efficient sensitisation of Er3+.Fully fluorinated complexes with P–O donor groups such as {[(C6F5)2PO]2N}3Er and [(C6F5)2PO2]3Er have a remarkably long-lived IR luminescence, with lifetimes of hundreds of microseconds [2,3]. However, these systems lack suitable chromophores that can act as photosensitisers for the excitation of erbium ions using low energy (visible light) photons.

We have been pleased to discover that co-sublimation of {[(C6F5)2PO]2N}3Er and a highly fluorescent, fully fluorinated zinc 2-(2-hydroxypheny)lbenzothiazole (FBTZ) complex produces a film in which there is efficient photosensitisation of erbium by the zinc complex. We have used this to demonstrate optical amplification in a planar waveguide [8] for which we have filed a patent [9]. We propose that future work on this project will examine the synthesis and physical properties of new metal complexes through some or all of the following structural modifications of Zn(FBTZ)2, with the aim of enhancing the efficiency of photosensitized excitation of lanthanide ions. Replacement of zinc by other metal ions (e.g. Co2+, which is similar in size to Zn2+ but has d-d transitions that allow it to function as a chromophore in its own right).

Replacement of selected fluorine atoms by heavier halogens, such as chlorine, so as to increase the rate of formation of electronically excited triplet states of the photosensitiser, thus facilitating energy transfer to lanthanide ions.

Synthesis of compounds with extended conjugation, e.g. by replacing individual benzene rings by fused ring systems such as naphthalene and heterocyclic analogues, thus increasing the molar extinction coefficient and shifting the absorption maxima to longer wavelengths.

Synthesis of compounds in which the metal is bound by the sulfur of a thiol rather than the oxygen of a phenol. This will favour the formation of complexes with softer metal ions of high atomic number, such as Pt(II), which should another way of enhancing triplet state formation. We also wish to form complexes of high atomic number metals such as Pt(II) and Ir(III) in which the metal atom is directly coordinated to carbon of the fluorinated aromatic ring. A complementary approach that we would also like to explore is through structural modification of the ligand in {[(C6F5)2PO]2N}3Er so as to shift its absorption into the visible range and to promote intersystem crossing to form excited state triplet ions. This, too, will involve the preparation of analogues in which isolated benzene rings are replaced by aromatic systems with more extended conjugation and the introduction of atoms with higher atomic number.

Eligibility

Applicant requirements are listed on the CONACYT foreign scholarship pages.

International students must provide evidence of proficient English language skills, see our entry requirements page for further information.

NB If you are interested in self-funding please contact Dr Wyatt by e-mail (p.b.wyatt@qmul.ac.uk) to discuss your eligibility for this project.

Application process

  1. Potential candidates should contact Dr Wyatt by e-mail (p.b.wyatt@qmul.ac.uk) and submit their CV and a cover letter explaining their eligibility and interest in this project.
  2. Applications to Queen Mary are accepted all year round but we encourage you to contact Dr Wyatt as soon as possible. If he agrees to take your application further you will be required to submit an online application.
  3. If you are successful we will give you an offer on the condition that you are given a funding award from CONACYT.
  4. When you have received a conditional offer from us, you should apply directly to CONACYT.

References:

1. R. H. C. Tan, M. Motevalli, I. Abrahams, P. B. Wyatt and W. P. Gillin, J. Phys. Chem. B, 2006, 110, 24476-24479
2. G. Mancino, A. J. Ferguson, A. Beeby, N. J. Long and T. S. Jones, J. Am. Chem. Soc. 2005, 127, 524-525
3. Y. Zheng, J. Pearson, R. H. C. Tan, W. P. Gillin and P. B. Wyatt, Journal of Materials Science: Materials in Electronics, 2009, 20, S430-S434
4. Y. Zheng, M. Motevalli, R. H. C. Tan, I. Abrahams, W. P. Gillin and P. B. Wyatt, Polyhedron, 2008, 27, 1503-1510
5. I. Hernández, Y.-X. Zheng, M. Motevalli, R. H. Tan, W. P. Gillin and P. B. Wyatt, Chem. Commun., 2013, 49, 1933-1935
6. Y. Peng, H. Ye, Z. Li, M. Motevalli, I Hernández, W. P. Gillin and P. B. Wyatt, J. Phys. Chem. Lett., 2014, 5, 1560-1563
7. Z. Li, A. Dellali, J. Malik, M. Motevalli, R. M. Nix, T. Olukoya, Y. Peng, H. Ye, W. P. Gillin, I. Hernández, and P. B. Wyatt, Inorganic Chemistry, 2013, 52, 1379-1387
8. H. Ye, Z. Li, Y. Peng, C-C Wang, T-Y Li, Y. Zheng, A. Sapelkin, G. Adamopoulos, I. Hernández, P.B. Wyatt and W.P. Gillin, Nature Materials, 2014, 13, (April 2014), 382-386
9. W. P. Gillin, I. Hernández and P. B. Wyatt, IPO Patent application 1311862.5, filed 3 July 2013

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