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

Abstract

A family of the diphosphines PPh₂C₂(C₆H₄)_nC₂PPh₂ (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 S₁→T₁ intersystem crossing is drastically reduced to 10⁹ s⁻¹ (4–7)–10¹⁰ s⁻¹ (1–3), so that the fluorescence radiative decay rate can compete or even dominates. The drastic O₂ quenching of phosphorescence demonstrates the unprotected nature of the emission chromophores in 1–7, as opposed to the well protected, O₂ independent phosphorescence in most multimetallic Au(I) clusters.