Harvesting fluorescence from efficient Tk → Sj (j, k > 1) reverse intersystem crossing for ππ* emissive transition-metal complexes
Journal
Journal of Physical Chemistry C
Journal Volume
117
Journal Issue
40
Pages
20494-20499
Date Issued
2013
Author(s)
Abstract
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 → T k probing gives the prominent blue 375 nm fluorescence, and this time-dependent pump-probe signal correlates well with the lifetime of the T 1 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 to be operative in the A-3 solid film and should be universally applicable to the transition-metal complexes possessing a dominant ππ* 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. © 2013 American Chemical Society.
SDGs
Type
journal article