Synthesis, characterization and photophysical properties of PPh2-C2-(C6H4)n-C2-PPh2 based bimetallic Au(I) complexes

A family of the diphosphines PPh(2)C(2)(C(6)H(4))(n)C(2)PPh(2) (n = 0-3), which possess a dialkynyl-arene spacer between the phosphorus atoms, was used for the synthesis of a series of bimetallic gold(I) complexes 1-7. Unlike the corresponding polynuclear Au(i) clusters, which show unique phosphorescence, 1-7 reveal dual emissions consisting of fluorescence and phosphorescence. The results are rationalized, in a semi-quantitative manner, by the trace (1-3) to zero (4-7) contribution of MLCT varying with the number of conjugated phenylene rings. As a result, unlike typical polynuclear Au(I) clusters with 100% triplet state population, the rate constant of the S(1)→T(1) intersystem crossing is drastically reduced to 10(9) s(-1) (4-7)-10(10) s(-1) (1-3), so that the fluorescence radiative decay rate can compete or even dominates. The drastic O(2) quenching of phosphorescence demonstrates the unprotected nature of the emission chromophores in 1-7, as opposed to the well protected, O(2) independent phosphorescence in most multimetallic Au(I) clusters.