Synthesis, Electrochemistry, Photophysics, and Photochemistry of a Novel Discrete Tetranuclear Copper(I) Sulfido Cluster

A novel tetranuclear copper(I) complex, [Cu-4{mu- (Ph2P)(2)NH}(4)(mu(4)-S)](PF6)(2) (1), was designed and synthesized. It was found to display intense and long-lived phosphorescence in the solid and solution states. The lowest-energy excited state was assigned as ligand-to-metal charge transfer (LMCT) [S-2- -> Cu-4] mixed with some metal-centered (ds/dp) character. In addition, the phosphorescent state of this complex was found to be quenched by pyridinium acceptors via an oxidative electron transfer quenching process. An excited-state reduction potential of - 1.74 V versus saturated salt calomel electrode was estimated through oxidative quenching studies with a series of structurally related pyridinium acceptors, indicative of its strong reducing power in the excited state. From the transient absorption difference spectrum of the tetranuclear copper(I) sulfido complex and 4(methoxycarbonyl)-N-methylpyridinium hexafluorophosphate, in addition to the characteristic absorption of the pyridinyl radical at ca. 395 nm, two absorption bands at ca. 500 and 660 nm were also observed. The former was assigned as an LMCT absorption [S2- -> Cu4] and the latter as an intervalence charge-transfer transition, associated with the mixed-valence species Cu-I/Cu-I/Cu-I/Cu-II.

Automated summary

In this study, a novel tetranuclear copper(I) complex was designed and synthesized, which exhibited intense and long-lived phosphorescence in the solid and solution states. The complex showed strong reducing power in the excited state, as demonstrated by oxidative quenching studies. Additionally, the transient absorption difference spectrum analysis revealed characteristic absorption and intervalence charge-transfer transitions in the complex.