Cyclometalated Au(III) complexes with alkynylphosphine oxide ligands: synthesis and photophysical properties.

A series of cyclometalated Au(III) complexes [Au(C^N^C)(C2-L-P(O)Ph2)] with C^N^C = 2,6-diphenylpyridine and alkynylphosphine oxide ligands (L = no linker, Au1; phenyl, Au2; biphenyl, Au3; naphthyl, Au4; anthracenyl, Au5) were synthesized and fully characterized by spectroscopic methods and single crystal XRD analysis. The complexes obtained exhibit triplet (Au1-Au3) and dual (Au4, Au5) emissions in solution, in the solid phase and in the PMMA film, whose characteristics depend on the linker's nature of the alkynylphosphine oxide ligand. The description of electronic transitions responsible for energy absorption and emission in Au(III) complexes was made on the basis of a detailed analysis of the results of DFT calculations and has shown to involve ILCT, LLCT and MLCT transitions of singlet and triplet nature. It was demonstrated that packing in the crystal affects the solid-state emission of Au(III) complexes, which differs from that in solution. Based on DFT calculations for the supramolecular dimer for Au1, it was shown that this phenomenon is the result of packing of the complex molecules in the crystal.