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The organic (optoelectronic) revolution

The organic (optoelectronic) revolution . What is optoelectronics? The study and application of electronic devices that source, detect and control light. solar cells. lasers. PM. LEDs. CRT. the classical devices use inorganic materials: Si, GaN, Y 2 O 2 S:Eu, YAG:Nd.

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The organic (optoelectronic) revolution

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  1. The organic (optoelectronic) revolution What is optoelectronics? The study and application of electronic devices that source, detect and control light solar cells lasers PM LEDs CRT • the classical devices use inorganic materials: Si, GaN, Y2O2S:Eu, YAG:Nd • 1987: Tang and van Slyke demonstrate the first organic optoelectronic device • nowadays:

  2. Advantages of organic versus inorganic LEDs • synthetic flexibility • tuning of chemical structure  different optical and electronic properties • (potentially) very cheap production • - low temperature • - scalable to large area • (potentially) very energy efficient • new paradigm in the field • ultra-thin and lightweight • self-luminescent  no backlighting • the substrates can be flexible or transparent

  3. Classes of organic emitters for OLEDs • purely organic dyes • - fluorescent (limited to 25% efficiency) • - broad emission bands • - photo-bleaching • organometallic complexes • - phosphorescent • (theoretical 100% efficiency) • - broad emission bands • - sensitivity to oxygen • lanthanide complexes with organic ligands • - first example: Kido, 1990

  4. Properties of lanthanide ions LnIII ground state [Xe]4fn, n = 0..14 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu • Shielding of 4f orbitals  • similar chemical properties • electrostatic bonding • variable geometry and CNs • hard acid behaviour blue  NIR • Fascinating optical properties: • luminescence from f-f transitions • characteristic emission for each ion • narrow emission bands • long excited-states lifetimes Applications in optoelectronics and bio-medicine

  5. Advantages of lanthanide complexes in optoelectronics • sharp emission  pure colors (no filters) • one ligand, different emission colors (even NIR) • no oxygen sensitivity and no photo-bleaching • easier coordination chemistry f-f transitions are forbidden the excited states cannot be efficiently populated directly

  6. Sensitization of lanthanide ions Indirect excitation by energy transfer from a suitable antenna to the lanthanide ion Light emission Antenna excitation Energy transfer • Antenna requirements: • excellent energy harvester • efficient inter-system crossing • matching electronic levels • Deactivation: • radiative processes (fluorescence, phosphorescence) • non-radiative processes (vibration-induced) • electronic processes (energy back-transfer) 1S ISC 3T ET absorption Antenna LnIII

  7. Antennas for lanthanides organic chromophores (pyridines, phenantroline) d-metal complexes (RuII, PtII, IrIII) matrixes (PVK, CBP)

  8. The design of lanthanide complexes • Connecting the antenna to negatively charged groups (carboxylate) Grenthe, J. Am. Chem. Soc.1961 Bunzli, Spectrosc. Lett.2007 Bunzli, Dalton Trans.2000 Latva, J. Lumin.1997 Mazzanti, Angew. Chem. Int. Ed.2005 • Associating the antenna to diketonate complexes • low stability • few structure-property relationships • difficult optimization

  9. Luminescent lanthanide architectures for optoelectronics • synthesize new stable lanthanide architectures • tuned absorption and emission properties by ligand design • investigate their potential for applications in optoelectronics • high denticity ligands with negatively charged groups • sensitizing antenna: - organic chromophores • - d-metal complexes

  10. Aime, Tetrahedron Lett.2002, 43, 783 Facchetti, Chem. Commun.2004, 1770 The tetrazole motif in coordination chemistry • carboxylate often used for lanthanide coordination • tetrazole - highly acidic, aromatic • tetrazolate could replace carboxylate • tuning of absorption wavelength • Tetrazole-based complexes of d-metals: • high thermodynamic stability • interesting properties Very few examples in lanthanide coordination chemistry! • no luminescent lanthanides • no comparative studies

  11. Lanthanide complexes based on pyridine-tetrazolates

  12. Design of tetrazole-based ligands terpyridine ligands – pentadentate bipyridine ligands – tetradentate pyridine ligands – tridentate • influence of tetrazolate on the properties of the complexes • direct comparison with carboxylate analogues

  13. Organic synthesis of terpyridine-based ligands Andreiadis et al, submitted; patent pending

  14. Organic synthesis of bipyridine-based ligands

  15. Organic synthesis of pyridine-based ligands Easy access to tetrazole-based ligands

  16. Lanthanide complexes with terpyridine-based ligands [Ln(L)2]-, Ln = Nd, Eu, Tb the tetrazole-based ligands are well adapted to lanthanide complexation Giraud, Inorg. Chem. 2008, 47, 3952-3954

  17. Lanthanide complexes with bipyridine-based ligands [Ln(L)2]-, Ln = Eu, Tb Andreiadis et al, submitted

  18. Lanthanide complexes with pyridine-based ligands [Ln(L)3]3-, Ln = Nd, Eu, Tb Andreiadis et al, submitted

  19. Increasing the solubility in chlorinated solvents Solubility – strong advantage for the applications in OLED devices (wet process) • ligand functionalization • change of counterion isolated as an oil

  20. Stability of tetrazolate-based complexes • stable without dissociation in air and wet methanol solutions • quantitative study by UV titration L2- L2- [EuL2]- [EuL]+ [EuL2]- [EuL]+ logβ2 = 11.8(4) logβ2 = 10.5(5) Comparable stability to carboxylate analogues

  21. Absorption properties of pyridine-based complexes [Ln(L)3]3- 4 3 ε / 104 cm-1M-1 2 1 0 250 275 300 325 350 Wavelength / nm aromatic tetrazolate  increase of absorption wavelength and intensity

  22. Absorption properties of bipyridine-based complexes 4 [Ln(L)2]- 3 2 ε / 104 cm-1M-1 1 0 250 275 300 325 350 375 400 Wavelength / nm

  23. Absorption properties of terpyridine-based complexes 10 8 6 ε / 104 cm-1M-1 4 [Ln(L)2]- 2 0 250 300 350 400 450 500 Wavelength / nm substituents  tuning of absorption wavelength and intensity

  24. Photophysical properties of terpyridine-based complexes Ligand triplet states Modulation of ligand triplet state

  25. Photophysical properties of terpyridine-based complexes Emission quantum yields [Ln(L)2]- Eu: 36% Tb: 35% Nd: 0.09 % Eu: 35% Tb: 6% Nd: 0.22% Eu: 29% Tb: 0.1% Eu: 28% Eu: 5% Nd: 0.29% Nd: 0.19% Modulation of ligand triplet state  Tuning of emission quantum yields Very good QY for Eu (35%) and Nd (0.29%)

  26. Photophysical properties of terpyridine-based complexes Emission quantum yields Terbium QY function of triplet state [Ln(L)2]- Eu: 36% Tb: 35% Nd: 0.09 % Eu: 35% Tb: 6% Nd: 0.22% Eu: 29% Tb: 0.1% Eu: 28% Eu: 5% Nd: 0.29% Nd: 0.19% Latva, J. Lumin.1997

  27. Photophysical properties of bipyridine-based complexes [Ln(L)2]- Eu: 45% Tb: 27% Eu: 54% Tb: 13% Eu: 63% Tb: 6% Measured after drying Similar tuning of emission quantum yields

  28. Photophysical properties of pyridine-based complexes [Ln(L)3]3- Eu: 61% Tb: 65% Nd: 0.21% Eu: 39% Eu: 24% * Tb: 22% * * Chauvin, Spectr. Lett. 2007, 40, 193 • excellent quantum yields • for pyridine-tetrazole complexes • solubility in chlorinated solvents Possible applications in OLEDs

  29. Neutral lanthanide diketonate complexes

  30. New approach towards neutral lanthanide complexes • Lanthanide complexes employed in optoelectronics • neutral (vacuum processing) • based on the β-diketonate motif • additional soft, neutral ligands • low stability • dissociation during processing Replacing neutral chromophores with negatively charged ones for increasing the stability of the complex Preliminary testing in OLED devices

  31. The terpyridine-monocarboxylate ligand Terpyridine carboxylic acid leads to stable homoleptic mono- or poly-metallic complexes Ln= Eu, Gd, Tb, Nd [Ln(L)2](OTf) ∩ [Ln (LnL2)6](OTf)9 Bretonnière, J. Am. Chem. Soc., 2002, 124, 9012 Chen, Inorg. Chem., 2007, 46, 625 formation of heteroleptic complexes with β-diketonate units:

  32. Synthesis and properties of the complexes QY = 41% • complexes stable in air and solution • good quantum yields QY = 13% Investigate potential applications in OLED devices

  33. Cs2CO3 Al (cathode) PVK : Ln complex PEDOT:PPS – – + glass substrate ITO (anode ) Preliminary testing in OLED devices Excellent film-forming properties (doping in PVK matrix) • Collaboration Dr. Pascal Viville (Univ. Mons) • testing in OLED devices (spin-coating) • classical device architecture • the OLED devices display promising results • rather low current intensities: 5.4 mA/cm2 at 25V (Eu) • 45 mA/cm2 at 20V (Tb) device optimization in progress

  34. Heterometallic iridium-europium complexes

  35. Sensitization of europium by d-metals Indirect excitation using d-transitional metals byinter-metallic communication • absorption at visible wavelength • sensitization of NIR emitting lanthanides • europium sensitization requires high energy IrIII complexes - modulation of emission energy by the coordinated ligands use blue-emitting Ir complexes Thompson et al. Inorg Chem 2005,44, 7992 Coppo, Angew. Chem. Int. Ed.,2005, 44, 1806

  36. Heterometallic complex - strategy and ligand design Connecting the metal ions by a completely covalent structure (stability) • terpyridine-tetrazolate motif for lanthanide complexation • several target ligands investigated

  37. Synthesis of iridium-based ligand

  38. Synthesis of iridium-based ligand • 1H NMR and X-ray diffraction studies prove the retention of Ir conformation during the synthesis

  39. Synthesis of the heterometallic complex [Eu(L)2]- 1H NMR indicates a similar structure to the mono-metallic lanthanide complexes

  40. Protophysical properties of the heterometallic complex QY = 0.96% ex 400 nm 2,5 2,0 ηIr-Eu = 85-90% 1,5 intensity / a.u. • iridium  europium energy transfer • residual emission from iridium 1,0 • Eu emission due exclusively to Ir • very good energy transfer efficiency selective excitation of Ir moiety 0,5 0,0 300 400 500 600 700 800 promising architecture wavelength / nm

  41. Final conclusions and perspectives • tetrazole-based antennas for lanthanide • combining stability with tuning • of absorption and emission properties  extending the work to other architectures (podates)  applications in OLEDs • improving the stability of neutral diketonate • complexes by using charged chromophores  applications in OLEDs and surface grafting • polyvalent stable heterometallic architecture • with very high Ir  Eu transfer efficiency  improving europium emission efficiency  extending the chemistry to other metals

  42. Acknowledgements Prof. Luisa DE COLA, Prof. Jean WEISS, Prof. Muriel HISSLER, Dr. Guy ROYAL Dr. Daniel IMBERT Dr. Jacques PECAUT Dr. Marinella MAZZANTI Dr. Renaud DEMADRILLE Yann KERVELLA, Dr. Bruno JOUSSELME, Prof. Alexander FISYUK Colette LEBRUN, Pierre-Alain BAYLE Dr. Pascal VIVILLE (Mons University), Prof. Jean-Claude BUNZLI (EPFL) my colleagues and friends European Community Marie Curie EST “CHEMTRONICS” MEST-CT-2005-020513

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