Synthesis and characterization of novel rhenium (I) complexes with large Stokes shift for applications in organic electroluminescent devices

Two novel tricarbonyl rhenium(I)(Re(I)) complexes with versatile building block (1,10-phenanthroline). i.e., Re-PPhen and Re-FPPhen (PPhen, 3,8-diphenyl-1,10-phenanthroline; FPPhen, 3,8-bis(4-fluorophenyl)-1,10-phenanthroline), were designed, synthesized and structurally characterized by FTIR, H-1 NMR and mass spectroscopy. The photophysical properties of two complexes were investigated in detail. The absorption bands centered at ca. 255-350 and 380-550 nm from two complexes were attributed to the ligand-centered pi ->pi* electronic transition and the metal-to-ligand charge transfer d pi(Re)->pi*(ligand) (MLCT) transition, respectively. Re-PPhen and Re-FPPhen exhibited broad (MLCT)-M-3 maximum emission around 572-580 nm with the full width of half maximum of ca. 90 nm. These complexes displayed a unique feature that was a remarkably high Stokes shift up to about 240 nm. Both of two complexes showed high photoluminescence quantum efficiencies (0.11, 0.13) and short luminescent lifetimes (0.21, 0.16 mu s), respectively. Re-PPhen and Re-FPPhen were thermally stable with high decomposition temperature in the range of 355-365 degrees C corresponding to 5% weight loss, indicating that two complexes were stable enough to be sublimated to fabricate organic electroluminescent devices. The electroluminescent devices based on doped Re-FPPhen complex showed very high luminance of 9293 cd m(-2) and reasonable luminance efficiency of 9.4 cd A(-1). All evidences showed that Re-PPhen and Re-FPPhen were potential candidates for applications in organic electroluminescent devices. (C) 2012 Elsevier B.V. All rights reserved.