Gupta Rahat, Sahni Priya, Jana Salil K, Negi Anshul, Pal Amlan K
Department of Chemistry, Indian Institute of Technology Jammu, Nagrota Bypass Road, Jammu and Kashmir-181221, India.
Dalton Trans. 2023 Oct 31;52(42):15597-15607. doi: 10.1039/d3dt01947k.
The development of Ir(III)-NHC phosphors that display deep-blue luminescence without sacrificing the high photoluminescence quantum yield (PLQY) has become a pivotal area of research. In this respect, two novel deep-blue Ir-NHC emitters (C1 and C2) with strategically designed pro-carbenic imidazolium ligands (L1 and L2) incorporating a heavy bromine atom at the ligand-scaffold were synthesized in good yields (∼80% for L1, L2 and 65% for C1, C2). The ground and excited state properties of the complexes were photophysically determined and the results were found to be in accordance with theoretical calculations at the DFT and TD-DFT levels. Due to the strong σ-donation of the carbene ligands, complexes C1 and C2 displayed oxidation at low anodic potentials. Both the complexes showed deep-blue emission either in solution ( ∼ 400-425 nm) or as PMMA-doped films of varying concentrations ( ∼ 400 nm) with an ∼15 times enhanced PLQY with respect to benchmark Ir-NHC complexes. The strategy of incorporating the heavy bromine atom to reduce the molecular vibrations in C1 and C2 was further supported by ∼250 times reduced non-radiative decay constants () and Huang-Rhys constants of C1 and C2 in comparison to those of the benchmark complexes. These facts were also supported by triplet frequency calculations of C1 and C2 to identify the absence of vibrations.
开发在不牺牲高光致发光量子产率（PLQY）的情况下呈现深蓝色发光的Ir(III)-NHC磷光体已成为一个关键的研究领域。在这方面，合成了两种新型的深蓝色Ir-NHC发光体（C1和C2），其具有经过精心设计的前卡宾咪唑鎓配体（L1和L2），在配体骨架上引入了重溴原子，产率良好（L1、L2约为80%，C1、C2约为65%）。通过光物理方法测定了配合物的基态和激发态性质，结果发现与DFT和TD-DFT水平的理论计算结果一致。由于卡宾配体的强σ供体作用，配合物C1和C2在低阳极电位下发生氧化。两种配合物在溶液中（约400 - 425 nm）或作为不同浓度的PMMA掺杂薄膜（约400 nm）时均呈现深蓝色发射，相对于基准Ir-NHC配合物，其PLQY提高了约15倍。与基准配合物相比，C1和C2中重溴原子的引入降低分子振动的策略还得到了约250倍降低的非辐射衰减常数（）和黄-里斯常数的进一步支持。C1和C2的三重态频率计算也证实了不存在振动，进一步支持了这些事实。
