Organic triplet emissions of arylacetylide moieties harnessed through coordination to [Au(PCy3)]+. Effect of molecular structure upon photoluminescent properties

A family of mono- and binuclear Cy₃P-supported gold(I) complexes containing various π-conjugated linear arylacetylide ligands, including the two homologous series (Cy₃P)Au(C≡CC₆H₄)_n-1 (C≡CPh) and (Cy₃P)Au(C≡CC₆H₄)_n C≡C≡Au(PCy₃) (n = 1-4), have been prepared. X-ray crystal analyses revealed no intermolecular aurophilic interactions in their crystal lattice. The lowest-energy singlet transitions are predominately intraligand in nature and exhibit both phenyl and acetylenic ¹(ππ*) character. Strong photoluminescence is detected in solid and solution states under ambient conditions, with lifetimes in the microsecond regime. For complexes with a single arylacetylide group, only phosphorescence from the arylacetylide ³(ππ*) state is observed. Vibrational spacings in the solid-state emission spectra can be attributed to a combination of phenyl ring deformation and symmetric phenyl ring and C≡C stretches. Additional delayed-fluorescence emission is recorded for complexes with multiple p-arylacetylide units, and this is attributed to a triplet-triplet annihilation process. The phosphorescence energy of these complexes are readily modified by altering the length of the conjugated arylacetylide system, while the intensity of phosphorescence relative to fluorescence decreases when the p-arylacetylide chain is elongated. Information regarding the nature and relative energies of arylacetylide singlet and triplet excited states has been derived from the two homologous series and extrapolated to polymeric arylacetylide species. The 3(ππ*) excited-state reduction potentials E° [Au⁺/Au*] (Au = 1a, 2, and 4) are estimated to be -1.80, -1.28, and -1.17 V versus SSCE, respectively.