Niazi Maryam, Maisuls Iván, Mai Lukas A, Schäfer Sascha A, Oster Alex, Diaz Lukas Santiago, Guldi Dirk M, Doltsinis Nikos L, Strassert Cristian A, Klein Axel
Department of Chemistry and Biochemistry, Institute for Inorganic and Materials Chemistry, Faculty for Mathematics and Natural Sciences, University of Cologne, Greinstraße 6, D-50939 Köln, Germany.
Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstraße 28/30, D-48149 Münster, Germany.
Molecules. 2025 Apr 24;30(9):1901. doi: 10.3390/molecules30091901.
In our research aimed at replacing precious transition metals like platinum with abundant base metals such as nickel for efficient triplet emitters, we synthesized and studied Ni(II) complexes [Ni(L)Cl]. These complexes containing the N^C^N cyclometalating dipyridyl-phenide ligand, equipped with pending H-bonding amine groups (NH(C₆H₅) (L) and NH(C₆H₅CH₂), ClL). Molecular structures determined from experimental X-ray diffractometry and density functional theory (DFT) calculations in the ground state showed marked deviation of the Cl coligand (ancillary ligand) from the ideal planar coordination, with τ values of 0.35 and 0.33, respectively, along with hydrogen bonding interactions of the ligand NH function with the Cl coligand. The complexes exhibit long-wavelength absorption bands at approximately 425 nm in solution, with the experimental spectra being accurately reproduced through time-dependent density functional theory (TD-DFT) calculations. Vibrationally structured emission profiles and steady-state photoluminescence quantum yields of 30% for [Ni(L)Cl] and 40% for [Ni(L)Cl] (along with dual excited state lifetimes in the ns and in the ms range) were found in frozen 2-methyl-tetrahydrofuran (2MeTHF) glassy matrices at 77 K. Furthermore, within a poly(methyl methacrylate) matrix, the complexes showed emission bands centered at around 550 nm within a temperature range from 6 K to 300 K with lifetimes similar to 77 K. Based on TD-DFT potential scans along the metal-ligand (Ni-N) coordinate, we found that in a rigid environment that restricts the geometry to the Franck-Condon region, either the triplet or the singlet state could contribute to the photoluminescence.
在我们旨在用镍等储量丰富的贱金属替代铂等稀有过渡金属以制备高效三线态发光体的研究中，我们合成并研究了镍（II）配合物[Ni(L)Cl]。这些配合物含有N^C^N环金属化二吡啶-苯基配体，并带有悬垂的氢键胺基（NH(C₆H₅) (L) 和NH(C₆H₅CH₂)，ClL）。通过实验X射线衍射法和基态密度泛函理论（DFT）计算确定的分子结构表明，Cl配体（辅助配体）与理想平面配位存在明显偏差，τ值分别为0.35和0.33，同时配体NH官能团与Cl配体存在氢键相互作用。这些配合物在溶液中于约425 nm处呈现长波长吸收带，通过含时密度泛函理论（TD-DFT）计算能准确重现实验光谱。在77 K的冷冻2-甲基-四氢呋喃（2MeTHF）玻璃基质中，发现[Ni(L)Cl]的振动结构发射谱和稳态光致发光量子产率为30%，[Ni(L)Cl]为40%（同时具有纳秒和毫秒范围内的双激发态寿命）。此外，在聚甲基丙烯酸甲酯基质中，这些配合物在6 K至300 K的温度范围内显示出以约550 nm为中心的发射带，其寿命与77 K时相似。基于沿金属-配体（Ni-N）坐标的TD-DFT势能扫描，我们发现，在将几何结构限制在弗兰克-康登区域的刚性环境中，三线态或单重态都可能对光致发光有贡献。
