文摘
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 鈫?Tk (k > 1) excitation followed by Tk 鈫?Sj (j, k > 1) intersystem crossing (ISC) back to the S1 state. Upon S0 鈫?S1 355 nm excitation, the S1 鈫?T1 intersystem crossing rate has been determined to be 8.9 脳 108 s鈥?. Subsequently, in a two-step laser pump鈥損robe experiment, following a 355 nm laser excitation, the 532 nm T1 鈫?Tk probing gives the prominent blue 375 nm fluorescence, and this time-dependent pump鈥損robe signal correlates well with the lifetime of the T1 state. Careful examination reveals the efficiency of Tk 鈫?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 鈫?Sj ISC, which is competitive with the rate of Tk 鈫?T1 internal conversion. This mechanism is also proven to be operative in the A-3 solid film and should be universally applicable to the transition-metal complexes possessing a dominant 蟺蟺* configuration in the lowest-lying states. From an energy point of view, the UV fluorescence (375 nm) generated by green (532 nm) excitation can be recognized as a signal up-conversion process.