Victor A. Montes, Grigory V. Zyryanov, Evgeny Danilov, Neeraj

1. Ultrafast Energy Transfer in Oligofluorene-AluminumBis(8-hydroxyquinoline)acetylacetone Coordination Polymers Victor A. Montes, Grigory V. Zyryanov, Evgeny Danilov, Neeraj Agarwal, Manuel A. Palacios, and Pavel Anzenbacher Jr.* J. Am. Chem. Soc., 2009, 131 (5), 1787-1795

2. Outline • Introduction Resonance energy transfer Organic light-emitting diode • Experiment Synthesis Optical properties Ultrafast energy migration Solid-state electroluminescence • Conclusions

3. Resonance Energy Transfer (RET) T. Förster in 1959 proposed the Förster theory of resonance energy transfer S*+Q → S+Q* http://micro.magnet.fsu.edu/primer/techniques/fluorescence/fret/fretintro.html

4. Emission spectra of Donor Absorption spectra of acceptor Overlaps Resonance Energy Transfer (RET) • Energy transfer is efficient when: 1.The energy donor and acceptor are separated by a short distance.(30~100 Å) 2.Photons emitted by the excited state of the donor can be absorbed directly by the acceptor. Et: efficiency of energy transfer R0: Förster distance r : distance between donor and acceptor

5. Principle of OLED Device Operation

6. OLED v.s LCD 萬能科技大學光電系張興華OLED投影片

7. Electroluminescence Layer Device structures Cathode : CsF:Al ElectroluminescenceLayer Hole Injection Layer :PEDOT:PSS Anode :Indium-tin-oxide 萬能科技大學光電系張興華OLED投影片

8. OLED v.s PLED 萬能科技大學光電系張興華OLED投影片

9. Structure of Alq3-type complexes Complex 2 Red-shift Montes, V. A; Pohl, R.; Shinar, J.; Anzenbacher, P., Jr. Chem.-Eur. J. 2006, 12, 4523.

10. Electroluminescence Spectra of Alq3-type Complexes Montes, V. A; Pohl, R.; Shinar, J.; Anzenbacher, P., Jr. Chem.-Eur. J. 2006, 12, 4523.

11. Oligofluorene :OF Alq2acac X.; Wang, Y.Appl. Phys. Lett. 2008, 92, 103305. Anzenbacher, P., Jr. Chem. Commun. 2007, 3708.

12. Synthesis of Oligofluorene • Pd(PPh3)4, Et4N+OH- in MeOH, toluene, 60°C • 1,4-cyclohexadiene, Pd-C (10%), isopropanol, reflux. Anzenbacher, P., Jr. Chem. Commun. 2007, 3708.

13. 1H NMR spectra of Oligofluorene Figure 1. 1H NMR spectra of the ditopic ligands. Residual CHCl3 signals are marked with an asterisk.

14. n Synthesis of Alq2(acac) and 1a-e 5 days Yield=76% ~ 98% Scheme 1. Synthesis of Alq2(acac) and Coordination Polymers 1a-e Using Tris(acetylacetonate)aluminum(III), and X-ray Structure of Alq2(acac)

15. 475 nm 340 nm UV-vis absorption spectra of 1a-e Table 1. Summarized Absorption Data for Bichromophoric Systems 1a-e Figure 2. UV-vis absorption spectra of 1a-e in a CH2Cl2 solution showing contribution of both oligofluorene (OF) and AlIII quinolinolate chromophores.

16. Emission spectraof 1a-e 410 nm 550 nm Figure 3.Corrected emission spectra of the coordination polymers 1a-e in CH2Cl2 upon excitation at 340 nm

17. Excitation spectra of 1a-e UV-vis absorption spectra of 1a-e Figure 4. Excitation spectra of the polymers when monitored at 550 nm.

18. Transient Absorption Spectra 清華大學化學研究所 2005 陳學穎碩士論文

19. Model 3 Model 2

20. Model compound 2 excitation at 475 nm ( -  * of Alq3) τ=9200 ps Figure 5. (A) Absorption and emission spectra of model compound 2. (C) Transient absorption spectra of 2 0.2 ps after pump pulse at 475 nm and its decay monitored at 750 nm (inset).

21. Model compound 3 excitation at 340 nm (  -  * of oligofluorene ) τ=642 ps Figure 5.(B) Absorption and emission spectra of model compound 3. (D) Transient absorption spectra of 3 0.2 ps after pump pulse at 340 nm and its decay monitored at 750 nm(inset).

22. Transient absorption spectra of 1a-e 520 nm 640 nm 0.2 ps after excitation at475 nm ( -  * of Alq3)

23. Transient absorption spectra of 1a-e 475 nm 0.2 ps after excitation at340 nm (  -  * of oligofluorene )

24. Transient absorption spectra for 1d τ=1.4 ps Figure 6. Left : Transient absorption spectra for 1d after excitation at 340 nm (0.5mW) at various times . Right : Exponential fit of the kinetic profile at 750 nm.

25. Table 2. Calculated Rate Constants for Energy Transfer in the Coordination Polymers 1c-e Monitored by Decay at 750 nm Rate Constants for Energy Transfer kET = Obs-1 - Fl-1 kET is the overall rate of energy transfer Obs is the lifetime observed for the spectral change in the transient experiment Fl represents the fluorescence lifetime

26. 1e Mechanism for Intramolecular Energy Transfer kET = keh+kfq keh = exciton hopping between the fluorene moieties kfq = strongly exothermic transfer from fluorene to AlIII quinolinolate

27. 1c 1d 1e Mechanism for Intramolecular Energy Transfer kET=keh+kfq kET=6.9x1011 (s-1) kET=7.1x1011 (s-1) kET=3.3x1011 (s-1) Figure 7. Schematic representation of the mechanism for intramolecular energy transfer as proposed for the behavior of the bichromophoric systems 1c-e.Only one pathway of energy migration is shown for simplicity purposes.

28. Simplified OLED architectures Cathode : CsF (10 Å) : Al (1200 Å) Electroluminescence Layer : 1a-c (600 Å) Hole Injection Layer : PEDOT:PSS (500 Å) Anode : Indium-tin-oxide

29. 1a-OLED external quantum efficiency of 1.2%. maximum luminance was 6000 cd/m2 turn-on voltage of ∼6 V Figure 8. Left: Electroluminescence spectra of 1a-OLED at a voltage of 9 V. The inset shows a photograph of the operating device. Right: I-V and luminance curves of the ITO/PEDOT:PSS/1a /CsF:Al OLED.

30. Conclusions • Novel coordination polymers comprising oligofluorene moieties of a varying size (n = 1-9) connected via aluminum(III) bis(8-quinolinolate)acetylacetone (Alq2(acac)) complexes were synthesized and their photophysical properties were studied. • The energy migration from oligofluorene to the quinolinolate moieties was observed proceeding at a rate order of 1011 s-1. • In the solid state, complete energy transfer from oligofluorene fragments to the quinolinolate centers was observed due to intermolecular energy transfer.