Photophysical properties, X-ray structures, electrochemistry, and DFT computational chemistry of osmium complexes

We report the synthesis of phosphorescent divalent osmium complexes of the form [Os(N–N)2(L–L) or Os(L–L)2(N–N)]2+ (PF6)2 where N–N is a derivative of 1,10-phenanthroline, and L–L is a diarsine or diphosphine ligand: 1,2-bis(dimethylphosphino)ethane, 1,2-bis(dicyclohexylphosphino)ethane, or 1,2-bis(dimethylarseno)benzene. X-ray structures have been determined, luminescent and electrochemical properties have been measured and DFT calculations have been performed on the complexes. The emission lifetime of complexes of structure Os(II)(L–L)2(N–N) are longer than the those of Os(II)(N–N)2(L–L). The DFT calculations show that there is significant mixing of the π−π∗ into the dπ−π∗ charge-transfer state for the complexes of the form Os(II)(L–L)2(N–N) resulting in a longer lived excited state. Through DFT calculations we were able to conclude that the HOMO of the complexes is a d orbital on the osmium while the LUMO is the b1(ψ) π∗ system of the phenanthroline. However, we found that the HOMO did not have the correct symmetry to enable strong charge transfer to the phenanthroline to be observed, and the strong MLCT transition observed in the spectra is the metal d HOMO(−1) to the b1 π∗ LUMO of the phenanthroline.

Graphical abstractOsmium complexes based upon derivatives of phenanthroline and diarsine or diphosphine have been synthesized and characterized. X-ray structures, absorbance, emission, and electrochemical potentials have been determined for the complexes. DFT calculations utilizing the code in DMol3 showed that the HOMO(−1)–LUMO was the observed strong charge-transfer transition in the UV spectra.Figure optionsDownload full-size imageDownload as PowerPoint slide