Department of Chemistry, Institute for Molecular Science and Fusion Technology , Kangwon National University , Chuncheon , Gangwon 24341 , Republic of Korea.
Inorg Chem. 2019 Sep 16;58(18):12358-12364. doi: 10.1021/acs.inorgchem.9b01948. Epub 2019 Sep 4.
Novel carbazole-conjugated salen-In complexes ( and ) were prepared and fully characterized by H and C NMR spectroscopy, elemental analysis, and high-resolution mass spectrometry. The major low-energy absorption bands at λ = 342 nm for and 391 nm for , respectively, are assigned to typical intramolecular charge transfer (ICT) transitions between the carbazole unit and the salen-In center. The solvatochromism effects in various organic solvents and their large Stokes shift distinctly supported the ICT nature. The photoluminescent spectra of and showed broad emission bands are centered at 459 nm (blue, λ = 354 nm) and 507 nm (green, λ = 396 nm) in THF, respectively, which are typical feature of CT transitions. In particular, showed 8-fold enhanced quantum efficiency relative to that of , at least 10-fold higher than those of the carbazole-free salen-In complexes. Such enhanced luminescence efficiency of originated from efficient radiative decay based on the ICT transition between the salen-In moieties and carbazole parts, as well as its structural rigidity in conversion process between the ground (S) and excited (S) states. In other words, exhibited low quantum yield due to its structural fluctuation, which is free rotation of both the appended carbazole moieties and bridged phenylene rings in conversion between the S and S structures. Theoretical calculations clearly supported these intriguing results. In addition, these salen-In complexes exhibited high thermal stability ( = 367 °C for and 406 °C for ) and electrochemical stability.
新型咔唑-共轭席夫碱-In 配合物（和）通过 H 和 C NMR 光谱、元素分析和高分辨率质谱法进行了充分的表征。主要的低能吸收带分别位于 λ = 342 nm（用于 ）和 391 nm（用于 ），这归因于咔唑单元和席夫碱-In 中心之间的典型分子内电荷转移（ICT）跃迁。在各种有机溶剂中的溶剂化变色效应及其大斯托克斯位移明显支持了 ICT 性质。和的光致发光光谱在 THF 中分别显示出 459 nm（蓝色，λ = 354 nm）和 507 nm（绿色，λ = 396 nm）的宽发射带，这是 CT 跃迁的典型特征。特别是，与 相比，显示出 8 倍的量子效率增强，至少比无咔唑的席夫碱-In 配合物高 10 倍。这种增强的发光效率源于基于席夫碱-In 部分和咔唑部分之间的 ICT 跃迁的有效辐射衰减，以及其在基态（S）和激发态（S）之间转换过程中的结构刚性。换句话说，由于其结构波动，即附加的咔唑部分和桥连的亚苯基环在 S 和 S 结构之间的转换过程中的自由旋转，导致量子产率较低。理论计算清楚地支持了这些有趣的结果。此外，这些席夫碱-In 配合物表现出高热稳定性（对于 为 367°C，对于 为 406°C）和电化学稳定性。
