Synthesis, Electrochemical and Photophysical Properties of 2,4,6‐Tripyridyl‐1,3,5‐Triazine‐Bridged Trinuclear Diimine Rhenium(I) Tricarbonyl Complexes

Two series of trinuclear diimine ReI tricarbonyl complexes bridged by 2,4,6‐tri(pyridin‐4‐yl)‐1,3,5‐triazine (L1) or 2,4,6‐tri(pyridin‐3‐yl)‐1,3,5‐triazine (L2) have been synthesized and characterized. These two series of trinuclear complexes show distinctly different photophysical and electrochemical properties. The L2‐bridged complexes exhibit strong luminescence and relatively long emission lifetimes in room‐temperature solution, which are typical of decay from 3MLCT excited states, whereas L1‐bridged complexes show only very weak luminescence and short lifetimes under the same experimental conditions. The prominent differences in photophysical behavior between these two groups of trinuclear complexes has been rationalized by energy gap law, which has been supported by detailed analysis of the steady state and time‐resolved luminescence of these complexes. Moreover, computational results indicated that a low‐lying excited state locates below 3MLCT states in the series of L1‐bridged complexes.