Cyclometallated Photoconductors: Attractive Complexes for Optoelectronic Applications Dr. Nicolas Godbert LASCAMM Unità INSTM della Calabria Universita della Calabria Dipartimento di Chimica CEMIF.CAL

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

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

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

AZPON-Pd PYPON-Pt BEPON-PdPYPON-Pd AZPON-Pt BEPON-Pt Selected Materials

Photoconduction of 1 micron thick film High absorptionLow absorption At 330 nm If < 0.1 Io At 300 nmAt 450 nm

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

BEPONPYPON HOMO LUMO AZPON HOMO Cyclometalated Moiety LUMO Schiff Base Moiety PHOTOGENERATION

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

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

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

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

Singlet States Triplet States Ground State photon Absorption Intersystem Crossing (ISC) Fluorescence Phosphorescence non-Radiative Decay Z Pd = 46Z Pt = 78 METAL ROLE: ELECTRONIC TRANSITIONS ISC probability increases with the Z 4

BEPON-Pd = ~ 4 ns BEPON-Pt = ~ 5 ns = ~ 4 s SOLUTION FILM = ~ 4 ns em : 466 nm em : 480 nm em : 538 nm em : 566 nm EMISSION DECAYS

= 1, cm 2 V -1 s -1 I SCLC = 9 CV 2 /8d 35 V/ m MOBILITY: BEPON-Pd Space Charge Limited Current d = 10 m

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

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

Increasing Mobility of charges

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

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