posted on 2016-02-23, 00:00authored byZhiqiang Wang, Caijun Zheng, Weizhou Wang, Chen Xu, Baoming Ji, Xiaohong Zhang
Two luminescent cationic heteroleptic
four-coordinate CuI complexes supported by N-heterocyclic
carbene ligand and diphosphine ligand were successfully prepared and
characterized. These complexes adopt typical distorted tetrahedral
configuration and have high stability in solid state. Quantum chemical
calculations show carbene units have contributions to both highest
occupied molecular orbitals and lowest unoccupied molecular orbitals
of these CuI–NHC complexes, the lowest-lying singlet
and triplet excitations (S0 → S1 and
S0 → T1) of [Cu(Pyim)(POP)](PF6) are dominated by metal-to-ligand charge transfer (MLCT)
transition, while the S0 → S1 and S0 → T1 excitations of [Cu(Qbim)(POP)](PF6) are mainly MLCT and ligand-centered transitions, respectively.
These CuI–NHC complexes show efficient long-lifetime
emissions (λem = 520 nm, τ = 79.8 μs,
Φ = 0.56 for [Cu(Pyim)(POP)](PF6), λem = 570 nm, τ = 31.97 μs (78.99%) and 252.2 μs
(21.01%), Φ = 0.35 for [Cu(Qbim)(POP)](PF6)) in solid
state at room temperature, which are confirmed as delayed fluorescence
by investigating the emissions at 77 K.