Electroswitchable photoluminescence activity: synthesis, spectroscopy, electrochemistry, photophysics, and X-ray crystal and electronic structures of [Re(bpy)(CO)3(C[triple bond]C[bond]C6H4[bond]C[triple bond]C)Fe(C5Me5)(dppe)][PF6](n) (n = 0, 1)

A novel heterobimetallic alkynyl-bridged complex, Re(bpy)(CO)(3)(Ctriple bond]Cbond]C(6)H(4)bond]Ctriple bond]C)Fe(C(5)Me(5))(dppe)], 1, and its oxidized species, Re(bpy)(CO)(3)(Ctriple bond]Cbond]C(6)H(4)bond]Ctriple bond]C)Fe(C(5)Me(5))(dppe)]PF(6)], 2, have been synthesized and their X-ray crystal structures determined. A related vinylidene complex, Re(bpy)(CO)(3)(Ctriple bond]Cbond]C(6)H(4)bond](H)Cdouble bond]C)Fe(C(5)Me(5))(dppe)]PF(6)], 3, has also been synthesized and characterized. The cyclic voltammogram of 1 shows a quasireversible reduction couple at -1.49 V (vs SCE), a fully reversible oxidation at -0.19 V, and a quasireversible oxidation at +0.88 V. In accord with the electrochemical results, density-functional theory calculations on the hydrogen-substituted model complex Re(bpy)(CO)(3)(Ctriple bond]Cbond]C(6)H(4)bond]Ctriple bond]C)Fe(C(5)H(5))(dHpe) (Cp = C(5)H(5), dHpe = H(2)Pbond](CH(2))(2)bond]PH(2)) (1-H) show that the LUMO is mainly bipyridine ligand pi* in character while the HOMO is largely iron(II) d orbital in character. The electronic absorption spectrum of 1 shows low-energy absorption at 390 nm with a 420 nm shoulder in CH(2)Cl(2), while that of 2 exhibits less intense low-energy bands at 432 and 474 nm and additional low-energy bands in the NIR at ca. 830, 1389, and 1773 nm. Unlike the related luminescent rhenium(I)-alkynyl complex Re(bpy)(CO)(3)(Ctriple bond]Cbond]C(6)H(4)bond]Ctriple bond]Cbond]H)], 4, complex 1 is found to be nonemissive, and such a phenomenon is attributed to an intramolecular quenching of the emissive d pi(Re) --> pi*(bpy) (3)MLCT state by the low-lying MLCT and LF excited states of the iron moiety. Interestingly, switching on of the luminescence property derived from the d pi(Re) --> pi*(bpy) (3)MLCT state can be demonstrated in the oxidized species 2 and the related vinylidene analogue 3 due to the absence of the quenching pathway.