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

The synthesis and photophysical properties of two new Re(I) complexes are reported: fac-Re(phenC triple-bond CH)(CO)(3)Cl (where phenC triple bond CH is 5-ethynyl-1,10-phenanthroline) and its Au(I)-acetylide analogue (fac-Re(phenC triple-bond CAuPPh(3))(CO)(3)Cl). Also reported are the photophysical measurements obtained for the benchmark fac-Re(phen)(CO)(3)Cl chromophore, as well as the phenC triple-bond CAuPPh(3) and phenC triple-bond 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 triple bond CH)(CO)(3)Cl, 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 ((3)IL) state, localized within the diimine ligand. The lowest excited state in fac-Re(phenC triple-bond CAuPPh(3))(CO)(3)Cl seems to result from an admixture of Re-based MLCT and (3)IL states resident on the phenC triple-bond 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(phenC triple-bond CAuPPh(3))(CO)(3)Cl is increased as a result of the glassy medium and the resulting excited state can be considered to be ligand-localized.