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

<p id="spar0010">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, ¹H NMR and mass spectroscopy. The photophysical properties of two complexes were investigated in detail. The absorption bands centered at ca. 255&ndash;350 and 380&ndash;550&nbsp;nm from two complexes were attributed to the ligand-centered &pi;&rarr;&pi;* electronic transition and the metal-to-ligand charge transfer d&pi;(Re)&rarr;&pi;*(ligand) (MLCT) transition, respectively. Re-PPhen and Re-FPPhen exhibited broad ³MLCT maximum emission around 572&ndash;580&nbsp;nm with the full width of half maximum of ca. 90&nbsp;nm. These complexes displayed a unique feature that was a remarkably high Stokes shift up to about 240&nbsp;nm. Both of two complexes showed high photoluminescence quantum efficiencies (0.11, 0.13) and short luminescent lifetimes (0.21, 0.16&nbsp;&mu;s), respectively. Re-PPhen and Re-FPPhen were thermally stable with high decomposition temperature in the range of 355&ndash;365&nbsp;&deg;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&nbsp;cd&nbsp;m^&minus;2 and reasonable luminance efficiency of 9.4&nbsp;cd&nbsp;A^&minus;1. All evidences showed that Re-PPhen and Re-FPPhen were potential candidates for applications in organic electroluminescent devices.</p><!--VALIDHTML-->