Cyclometallated Photoconductors: Attractive Complexes for Optoelectronic Applications

1. CENTRO DI ECCELLENZA UNIVERSITA' della CALABRIA MATERIALI FUNCTIONAL FUNZIONALI NANOSTRUCTURED NANOSTRUTTURATI MATERIALS   Universita’ della Calabria Dipartimento di Chimica LASCAMM Unità INSTM della Calabria CEMIF.CAL Cyclometallated Photoconductors: Attractive Complexes for Optoelectronic Applications Dr. Nicolas Godbert

2. New Class of Photorefractive Materials BEPON AZPON Amorphous State Dissolved in PIBMA (60 %) Efficiency max around Tg: 24ºC Adv. Mater., 2002, 1233-1236 J. Am. Chem. Soc, 2001, 5598-5599

3. Photorefractivity Photogeneration Transport Trapping Space Charge Field Induction Refractive Index Modulation Photoconductors Photorefractive

4. INVESTIGATIONS TOWARDS IMPROVEMENTS OF PHOTOCONDUCTION Photogeneration Should depends on chemical Structure of the compounds Charge Mobility: Holes or Electrons Should depends on chemical structure (HOMO/LUMO) and the physical organization of the material

5. Selected Materials AZPON-Pd BEPON-Pd PYPON-Pd BEPON-Pt PYPON-Pt AZPON-Pt

6. Photoconduction of 1 micron thick film At 300 nm At 330 nm At 450 nm High absorption Low absorption If < 0.1 Io

7. Photoconduction Palladium vs. Platinum lmax: 460 nm lmax: 470 nm Pypon Pd: 6.9 mm thick film Pypon Pt: 7.2 mm thick film Difference of 2 orders of magnitude

8. PHOTOGENERATION LUMO Schiff Base Moiety HOMO Cyclometalated Moiety AZPON HOMO LUMO HOMO LUMO PYPON BEPON

9. PHOTOGENERATION HOMO/LUMO localisations HOMO/LUMO distribution space separated A comparison between S0 and S1 geometries LUMO situated on the Cyclometalated Moiety HOMO situated on the Schiff Base Moiety Twisted Excited State

10. PHOTOGENERATION Structural Properties: Palladium versus Platinum Quantum Efficiency of Photogeneration l : 533 nm Intrinsec photoconduction • Neglecting trapping • Weak Absorpion • E. Hendrickx, et al, J. Chem. Phys., 112, 9557 (2000).

11. METAL ROLE: ELECTRONIC TRANSITIONS UV-Vis Spectrum Deconvolution BEPON-Pd

12. METAL ROLE: ELECTRONIC TRANSITIONS Jablonski Electronic Level Diagram Probable Intersystem Crossing

13. METAL ROLE: ELECTRONIC TRANSITIONS Singlet States Intersystem Crossing (ISC) Triplet States Absorption Fluorescence non-Radiative Decay Phosphorescence photon Ground State ISC probability increases with the Z4 ZPd= 46 ZPt = 78

14. EMISSION DECAYS BEPON-Pd BEPON-Pt lem: 466 nm lem: 480 nm SOLUTION t= ~ 5 ns t= ~ 4 ns lem: 538 nm lem: 566 nm t= ~ 4 ns t= ~ 4 ms FILM

15. MOBILITY: BEPON-Pd Space Charge Limited Current ISCLC = 9mCV2/8d3 • = 1,3 10-9 cm2V-1s-1 @ 35 V/mm d = 10 mm

16. Towards Optoelectronic Applications Tuning of Absoprtion Properties Chemical Modifications on Ligands From UV to near IR photoconduction Increasing Mobility of charges Control of material supramolecular organisation Increasing Life Time of Excited States h e- e(h)

17. Tuning of Absorption Properties Bepon Azpon derivative 1 Azpon derivative 3 Azpon derivative 2 Tuning of the LUMO level: CM Ligand Tuning of the HOMO level: Schiff Base Azpon derivative 4

18. Increasing Mobility of charges

19. Increasing Life Time of Excited States Collaborating with Dr N. Bellec and Prof. D. Lorcy University of Rennes I (France) First Pd Complexe covalently linked to TTF donnor moiety

20. Acknowledgments Prof. Mauro Ghedini and Prof. Attilio Golemme Dr Roberto Termine, Dr. Mara Talarico and Dr Iolinda Aiello Dr. Mario Amati, Dr. Sandra Belviso and Prof. Francesco Lelj, Dr Nathalie Bellec and Prof. Dominique Lorcy For funding ! LASCAMM Unità INSTM della Calabria