Near-Infrared Spin-Flip Luminophores with Earth-abundant Metal Ions 2.0 (NIR-SPINFLIP 2.0)

发光金属配合物在有机发光二极管等领域有着广泛的应用。目前，这些技术主要依赖于昂贵的金属前驱体，而基于廉价且地球上丰富的金属离子的高效发光体迄今为止还很少见。由于电子激发的金属络合物的许多非辐射衰变途径的普遍存在，通常导致低发光效率，因此开发在近红外（NIR）光谱区域发射的材料特别具有挑战性。该项目将开发和调整基于地球上丰富的具有d3和d2电子构型的金属离子（主要是钒和钼离子）的分子自旋翻转近红外发射器。对于3d 2钒（III）和3d 3钒（II）金属离子，强配体将以假八面体配位几何结构配位，以增加钒的固有弱配体场分裂，并将构型间配体场激发态的能量推到发射自旋翻转态之上。这将阻止到这些暗态的后系统间穿越（后ISC）。在配体上安装溴或碘取代基以利用重原子效应将有利于ISC路径从初始激发态到自旋翻转态。为了增加自旋翻转发射的辐射速率，杂配的非中心对称配合物用于减轻拉波特规则。系统的配位体和CH/CD泛音测量的氘化服务，以了解和减少非辐射衰变通过多声子弛豫。通过这些组合策略，我们将开发一种基于钒（III/II）氧化还原电对的氧化还原可切换发光（RSL）平台，其中两种氧化态都显示发光，这与传统的氧化还原可切换开/关发光体不同。对于已经具有固有的大配体场分裂和自旋轨道耦合常数的4d金属离子钼（III），将开发基于弱场配体的互补策略，并将在自旋翻转态略上方安装电荷转移态作为有效布居自旋翻转态的天线。ISC速率将由泵浦-探测光谱确定。步进扫描FTIR光谱将探测自旋翻转态的结构，而近红外光致发光将在各种环境中通过静态和时间分辨光谱进行研究。DFT计算和多参考计算是对光谱研究的补充，其结果将加深我们对过渡金属配合物激发态衰变过程的理解，并将进一步系统地改进涉及金属配合物的许多关键技术，如光通信或近红外生物医学成像。

Luminescent metal complexes are important building blocks in many applications such as organic light-emitting diodes. Currently, these technologies mainly rely on expensive metal precursors, while efficient luminophores based on cheap and earth-abundant metal ions are rare up to now. The development of materials that emit in the near-infrared (NIR) spectral region is particularly challenging due to the prevalence of many non-radiative decay pathways of electronically excited metal complexes, usually leading to low luminescence efficiencies. This project will develop and tune molecular spin-flip NIR emitters based on earth-abundant metal ions with d3 and d2 electron configurations (primarily vanadium and molybdenum ions). For the 3d2 vanadium(III) and 3d3 vanadium(II) metal ions, strong ligands will be coordinated in a pseudo-octahedral coordination geometry to increase the intrinsically weak ligand field splitting of vanadium and to push the energy of the interconfigurational ligand field excited states above the emissive spin-flip states. This will block the back-intersystem crossing (back-ISC) to these dark states. Installing bromine or iodine substituents at the ligands to exploit the heavy-atom effect will favor the ISC path from initially excited states to the spin-flip states. To increase the radiative rate for the spin-flip emission, heteroleptic, non-centrosymmetric complexes serve to mitigate Laporte’s rule. Systematic deuteration of the ligands and CH/CD overtone measurements serve to understand and decrease non-radiative decay via multiphonon relaxation. With these combined strategies, we will develop a redox-switchable luminescence (RSL) platform based on the vanadium(III/II) redox couple where both oxidation states exhibit luminescence in contrast to conventional redox-switchable on/off emitters.For the 4d metal ion molybdenum(III), which already possesses intrinsically large ligand field splittings and spin-orbit coupling constants, complementary strategies based on weak-field ligands and the installation of charge-transfer states slightly above the spin-flip states as antennas for efficient population of the spin-flip states will be developed.ISC rates will be determined by pump-probe spectroscopy. Step-scan FTIR spectroscopy will probe the structure of the spin-flip states, while NIR photoluminescene will be investigated by static and time-resolved spectroscopy in various environments. DFT calculations augmented by multireference calculations complement the spectroscopic studies.The results will deepen our understanding of excited state decay processes of transition metal complexes and further the systematic improvement for many key technologies involving metal complexes such as optical telecommunications or NIR biomedical imaging.