Brightly Blue and Green Emitting Cu(I) Dimers for Singlet Harvesting in OLEDs
Brightly Blue and Green Emitting Cu(I) Dimers for Singlet Harvesting in OLEDs
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DOI：
10.1021/jp402975d
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发表时间：
2013-11-21
影响因子：
2.9
通讯作者：
Yersin, Hartmut
中科院分区：
文献类型：
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作者：
Leitl, Markus J.;Kuechle, Fritz-Robert;Yersin, Hartmut
利用螯合氨基膦配体Ph2P-(o-C6H4)- n (CH3)(2) （PNMe2）和Ph2P-(o-C6H4)- nc4h8 (PNpy)，合成了4个卤化物（Cl, Br， I）桥接铜配位化合物[Cu(mu-Cl)(PNMe2)](2)(1)、[Cu(mu-Br)(PNMe2)]（2)(2)）、[Cu(mu-I)(PNMe2)](2)(3)和[Cu(mu-I)(PNpy)](2)(4)并进行了结构表征。对其光物理性质进行了详细的研究。该配合物表现出强烈的蓝色(λ (max) = 464（3)和465 nm(4)）和绿色(λ (max) = 506（1)和490 nm(2)）发光，在衰减时间短至4.1 μ s的情况下，量子产率高达65%。对1.3和300 K之间的发射衰减行为的研究有助于深入了解发射状态的性质。在温度低于约60 K时，所研究化合物的衰变时间为数百微秒长，这表明发射来自三重态（T-1态）。DFT计算表明，该态具有（金属+卤化物）到配体的电荷转移(3)(M+X)LCT特征。在1.3 K下的研究使我们能够深入了解三个三重态，特别是确定单个亚态的衰变时间长达几毫秒。零场分裂小于1或2厘米（-1）。通过对这些数据的分析，可以得出自旋轨道耦合（SOC）有效性的结论。有趣的是，在三重态性质中，卤化物的荷电常数差异并不明显。当温度从t60增加到300k时，发射衰减时间显著减少了近2个数量级，而在环境温度下，衰减时间仅为4-7 μ s左右，而发射量子产率没有显著降低。这种（辐射）衰减时间的急剧减少是短寿命单重态（S-1态）的热居群的结果，它的能量仅比T-1态高几百波数（460-630 cm(-1)）。这种发射机制对应于热激活延迟荧光（TADF）。在环境温度下，几乎只观察到延迟荧光（类似于98%）。显示这种机制的化合物对oled或LEECs的应用具有很高的吸引力，因为原则上，可以在最低激发的单重态下收集所有的单重态和三重态激子以产生光。这种效应代表了单线态收获机制。
With the chelating aminophosphane ligands Ph2P-(o-C6H4)-N(CH3)(2) (PNMe2) and Ph2P-(o-C6H4)-NC4H8 (PNpy), the four halide (Cl, Br, I)-bridged copper coordination compounds [Cu(mu-Cl)(PNMe2)](2) (1), [Cu(mu-Br)(PNMe2)](2) (2), [Cu(mu-I)(PNMe2)](2) (3), and [Cu(mu-I)(PNpy)](2) (4) were synthesized and structurally characterized. Their photophysical properties were studied in detail. The complexes exhibit strong blue (lambda(max) = 464 (3) and 465 nm (4)) and green (lambda(max) = 506 (1) and 490 nm (2)) luminescence as powders with quantum yields of up to 65% at decay times as short as 4.1 mu s. An investigation of the emission decay behavior between 1.3 and 300 K gives insight into the nature of the emitting states. At temperatures below T approximate to 60 K, the decay times of the studied compounds are several hundred microseconds long, which indicates that the emission originates from a triplet state (T-1 state). DFT calculations show that this state is of (metal+halide)-to-ligand charge transfer (3)(M+X)LCT character. Investigations at 1.3 K allow us to gain insight into the three triplet substates, in particular, to determine the individual substate decay times being as long as a few milliseconds. The zero-field splittings are smaller than 1 or 2 cm(-1). With an analysis of these data, conclusions about the effectiveness of spin-orbit coupling (SOC) can be drawn. Interestingly, the large differences of SOC constants of the halides are not obviously displayed in the triplet state properties. With a temperature increase from T 60 to 300 K, a significant decrease of the emission decay time by almost 2 orders of magnitude is observed, and at ambient temperature, the decay times amount only to similar to 4-7 mu s without a significant reduction of the emission quantum yields. This drastic decrease of the (radiative) decay time is a result of the thermal population of a short-lived singlet state (S-1 state) that lies energetically only a few hundred wavenumbers (460-630 cm(-1)) higher than the T-1 state. Such an emission mechanism corresponds to a thermally activated delayed fluorescence (TADF). At ambient temperature, almost only a delayed fluorescence (similar to 98%) is observed. Compounds showing this mechanism are highly attractive for applications in OLEDs or LEECs as, in principle, it is possible to harvest all singlet and triplet excitons for the generation of light in the lowest excited singlet state. This effect represents the singlet harvesting mechanism.