Lee Sumin, Lee Yongmoon, Kim Kyungmin, Heo Seunga, Jeong Dong Yeun, Kim Sangsub, Cho Jaeheung, Kim Changsoon, You Youngmin
Division of Chemical Engineering and Materials Science, and Graduate Program in System Health Science and Engineering, Ewha Womans University, Seoul 03760, Republic of Korea.
Graduate School of Convergence Science and Technology, and Inter-University Semiconductor Research Center, Seoul National University, Seoul 08826, Republic of Korea.
Inorg Chem. 2021 Jun 7;60(11):7738-7752. doi: 10.1021/acs.inorgchem.1c00070. Epub 2021 Mar 24.
Circularly polarized luminescence (CPL) enables promising applications in asymmetric photonics. However, the performances of CPL molecules do not yet meet the requirements of these applications. The shortcoming originates from the trade-off in CPL between the photoluminescence quantum yield (PLQY) and the photoluminescence dissymmetry factor (). In this study, we developed a molecular strategy to circumvent this trade-off. Our approach takes advantage of the strong propensity of [Pt(N^C^N)Cl], where the N^C^N ligand is 1-(2-oxazoline)-3-(2-pyridyl)phenylate, to form face-to-face stacks. We introduced chiral substituents, including ()-methyl, ()- and ()-isopropyl, and ()-indanyl groups, into the ligand framework. This asymmetric control induces torsional displacements that give homohelical stacks of the Pt(II) complexes. X-ray single-crystal structure analyses for the ()-isopropyl Pt(II) complex reveal the formation of a homohelical dimer with a Pt···Pt distance of 3.48 Å, which is less than the sum of the van der Waals radii of Pt. This helical stack elicits the metal-metal-to-ligand charge-transfer (MMLCT) transition that exhibits strong chiroptical activity due to the electric transition moment making an acute angle to the magnetic transition moment. The PLQY and values of the MMLCT phosphorescence emission of the ()-isopropyl Pt(II) complex are 0.49 and 8.4 × 10, which are improved by factors of ca. 6 and 4, respectively, relative to the values of the unimolecular emission (PLQY, 0.078; , 2.4 × 10). Our photophysical measurements for the systematically controlled Pt(II) complexes reveal that the CPL amplifications depend on the chiral substituent. Our investigations also indicate that excimers are not responsible for the enhanced chiroptical activity. To demonstrate the effectiveness of our approach, organic electroluminescence devices were fabricated. The MMLCT emission devices were found to exhibit simultaneous enhancements in the external quantum efficiency (EQE, 9.7%) and the electroluminescence dissymmetry factor (, 1.2 × 10) over the unimolecular emission devices (EQE, 5.8%; , 0.3 × 10). These results demonstrate the usefulness of using the chiroptically active MMLCT emission for achieving an amplified CPL.
圆偏振发光（CPL）在不对称光子学中有着广阔的应用前景。然而，CPL分子的性能尚未满足这些应用的要求。这一缺点源于CPL在光致发光量子产率（PLQY）和光致发光不对称因子（）之间的权衡。在本研究中，我们开发了一种分子策略来规避这种权衡。我们的方法利用了[Pt(N^C^N)Cl]（其中N^C^N配体为1-(2-恶唑啉)-3-(2-吡啶基)苯酸盐）形成面对面堆叠的强烈倾向。我们将手性取代基，包括()-甲基、()-和()-异丙基以及()-茚满基，引入配体框架。这种不对称控制诱导了扭转位移，从而形成了Pt(II)配合物的同手性螺旋堆叠。对()-异丙基Pt(II)配合物的X射线单晶结构分析表明，形成了一种同手性二聚体，Pt···Pt距离为3.48 Å，小于Pt的范德华半径之和。这种螺旋堆叠引发了金属-金属到配体的电荷转移（MMLCT）跃迁，由于电跃迁矩与磁跃迁矩成锐角，该跃迁表现出很强的手性光学活性。()-异丙基Pt(II)配合物的MMLCT磷光发射的PLQY和值分别为0.49和8.4×10，相对于单分子发射的值（PLQY，0.078；，2.4×10）分别提高了约6倍和4倍。我们对系统控制的Pt(II)配合物的光物理测量表明，CPL放大取决于手性取代基。我们的研究还表明，激基缔合物不是增强手性光学活性的原因。为了证明我们方法的有效性，制备了有机电致发光器件。发现MMLCT发射器件相对于单分子发射器件（EQE，5.8%；，0.3×10），其外量子效率（EQE，9.7%）和电致发光不对称因子（，1.2×10）同时得到了提高。这些结果证明了使用具有手性光学活性的MMLCT发射来实现放大的CPL的有用性。
