Influence of a gold(I)-acetylide subunit on the photophysics of Re(phen)(CO) ₃Cl

The synthesis and photophysical properties of two new Re(l) complexes are reported: fac-Re(phenC≡CH)(CO) ₃Cl (where phenC≡CH is 5-ethynyl-1,10-phenanthroline) and its Au(l)-acetylide analogue (fac-Re(phenC≡CAuPPh ₃)(CO) ₃-Cl). Also reported are the photophysical measurements obtained for the benchmark fac-Re(phen)(CO) ₃Cl chromophore, as well as the phenC≡CAuPPh ₃ and phenC≡CH ligands. The unstable nature of the precursor gold-containing ligand illustrates the advantage of using the "chemistry on the complex" approach, which facilitated preparation of the Re-Au binuclear complex. Where possible, all compounds were studied by static and transient absorption (TA), as well as steady-state and time-resolved photoluminescence (TRPL), at room temperature (RT) and 77 K, as well as nanosecond time-resolved infrared (TRIR) spectroscopy. The spectroscopic information provided by these techniques enabled a thorough evaluation of excited-state decay in most cases. In fac-Re(phenC≡CH)-(CO) ₃Cl, the RT excited-state decay is most consistent with a metal-to-ligand charge transfer (MLCT) assignment, whereas at 77 K, the lowest excited state is dominated by the triplet intraligand ( ³IL) state, localized within the diimine ligand. The lowest excited state in fac-Re(phenC≡CAuPPh ₃)(CO) ₃Cl seems to result from an admixture of Re-based MLCT and ³IL states resident on the phenC≡CAuPPh ₃ moiety. TA and TRIR methods indicate that these excited states are thermally equilibrated at room temperature. At 77 K, the MLCT energy of fac-Re(phen-C≡CAuPPh ₃)(CO) ₃Cl is increased as a result of the glassy medium and the resulting excited state can be considered to be ligand-localized.