| Popis: |
Using a bimetallic Au(I) complex bearing alkynyl-(phenylene)3-diphosphine ligand (A-3), we demonstrate that the fluorescence can be exquisitely harvested upon T1 → Tk (k > 1) excitation followed by Tk → Sj (j, k > 1) intersystem crossing (ISC) back to the S1 state. Upon S0 → S1 355 nm excitation, the S1 → T1 intersystem crossing rate has been determined to be 8.9 × 108 s–1. Subsequently, in a two-step laser pump–probe experiment, following a 355 nm laser excitation, the 532 nm T1 → Tk probing gives the prominent blue 375 nm fluorescence, and this time-dependent pump–probe signal correlates well with the lifetime of the T1 state. Careful examination reveals the efficiency of Tk → Sj (j, k > 1) reverse intersystem crossing to be 5.2%. The result is rationalized by a mechanism incorporating substantial involvement of metal-to-ligand charge transfer (MLCT) in the Tk (Sj) states, enhancing the rate of Tk → Sj ISC, which is competitive with the rate of Tk → T1 internal conversion. This mechanism is also proven ... |
