Halide-Enhanced Spin-Orbit Coupling and the Phosphorescence Rate in Ir(III) Complexes.
Halide-Enhanced Spin-Orbit Coupling and the Phosphorescence Rate in Ir(III) Complexes.
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DOI：
10.1021/acs.inorgchem.0c02469
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发表时间：
2021-01
影响因子：
4.6
通讯作者：
M. Shafikov;A. Zaytsev;V. N. Kozhevnikov
中科院分区：
文献类型：
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作者：
M. Shafikov;A. Zaytsev;V. N. Kozhevnikov
Ir（III）配合物中磷光的自旋禁戒性质通过金属诱导的自旋轨道耦合（SOC）效应而得到放松。磷光速率的进一步增加可以通过引入能够进一步增强SOC效应的额外中心来实现，例如金属配位卤化物。在此，我们提出了一个双核Ir（III）配合物Ir 2 I2，包含两个Ir（III）-碘化物部分。在室温下，该配合物在脱气的甲苯溶液中显示出强烈的磷光，荧光量子产率ΦPL（300 K）= 90%，亚微秒衰减时间τ（300 K）= 0.34 μs。这些值对应于最高值T1 → S 0磷光速率kr = 2.65 × 106 s-1。在低温下的研究使我们能够确定发射态T1的零场分裂（π），π（III-I）= 170 cm-1和T1子态异常短的单个衰变时间：τ（I）= 6.4 μs，τ（II）= 7.6 μs，τ（III）= 0.05 μs。这表明具有单重态的状态T1的强SOC。理论研究表明，具有单线态的T1态的SOC也是由卤化物贡献的。强烈地有助于络合物的较高占据分子轨道（例如，HOMO、HOMO - 1等），碘化物作为重要的SOC中心与金属协同工作。Ir 2 I2和早期报道的类似络合物Ir 2Cl 2的例子表明，金属配位的卤化物可以增强状态T1的SOC与单线态，因此，磷光率。Ir 2 I2和Ir 2Cl 2的比较研究表明，卤化物的份额在总贡献（卤化物加金属）与单线态T1的SOC强烈增加后，交换氯化物碘化物。交换也导致了T1态的π值从Ir 2Cl 2的π（III-I）= 205 cm-1降低到Ir 2 I2的T1 π（III-I）= 170 cm-1。这导致最快发射T1亚态III的更有效的热布居，从而进一步增强室温磷光速率。
The spin-forbidden nature of phosphorescence in Ir(III) complexes is relaxed by the metal-induced effect of spin-orbit coupling (SOC). A further increase of the phosphorescence rate could potentially be achieved by introducing additional centers capable of further enhancing the SOC effect, such as metal-coordinated halides. Herein, we present a dinuclear Ir(III) complex Ir2I2 that contains two Ir(III)-iodide moieties. The complex shows intense phosphorescence with a quantum yield of ΦPL(300 K) = 90% and a submicrosecond decay time of only τ(300 K) = 0.34 μs, as measured under ambient temperature for the degassed toluene solution. These values correspond to a top value T1 → S0 phosphorescence rate of kr = 2.65 × 106 s-1. Investigations at cryogenic temperatures allowed us to determine the zero-field splitting (ZFS) of the emitting state T1 ZFS(III-I) = 170 cm-1 and unusually short individual decay times of T1 substates: τ(I) = 6.4 μs, τ(II) = 7.6 μs, and τ(III) = 0.05 μs. This indicates a strong SOC of state T1 with singlet states. Theoretical investigations suggest that the SOC of state T1 with singlets is also contributed by halides. Strongly contributing to the higher occupied molecular orbitals of the complex (e.g., HOMO, HOMO - 1, and so forth), iodides work as important SOC centers that operate in tandem with metals. The examples of Ir2I2 and of earlier reported analogous complex Ir2Cl2 reveal that the metal-coordinated halides can enhance the SOC of state T1 with singlets and, consequently, the phosphorescence rate. A comparative study of Ir2I2 and Ir2Cl2 shows that the share of halides in total contribution (halides plus metals) to the SOC of state T1 with singlets increases strongly upon exchange of chlorides for iodides. The exchange also led to the decrease in values of ZFS of the T1 state from ZFS(III-I) = 205 cm-1 for Ir2Cl2 to T1 ZFS(III-I) = 170 cm-1 for Ir2I2. This results in a more efficient thermal population of the fastest emitting T1 substate III, thus further enhancing the room-temperature phosphorescence rate.