Reichenauer Florian, Wang Cui, Förster Christoph, Boden Pit, Ugur Naz, Báez-Cruz Ricardo, Kalmbach Jens, Carrella Luca M, Rentschler Eva, Ramanan Charusheela, Niedner-Schatteburg Gereon, Gerhards Markus, Seitz Michael, Resch-Genger Ute, Heinze Katja
Department of Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
Division Biophotonics, Federal Institute for Materials Research and Testing (BAM), Richard-Willstätter-Str. 11, 12489 Berlin, Germany.
J Am Chem Soc. 2021 Aug 4;143(30):11843-11855. doi: 10.1021/jacs.1c05971. Epub 2021 Jul 23.
Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge transfer states described by spatially separated orbitals, the energies of spin-flip states cannot straightforwardly be predicted as Pauli repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence. The spin-flip emission band of the chromium complex [Cr(bpmp)] (bpmp = 2,6-bis(2-pyridylmethyl)pyridine) shifted to higher energy from ca. 780 nm observed for known highly emissive chromium(III) complexes to 709 nm. The photoluminescence quantum yields climb to 20%, and very long excited state lifetimes in the millisecond range are achieved at room temperature in acidic DO solution. Partial ligand deuteration increases the quantum yield to 25%. The high excited state energy of [Cr(bpmp)] and its facile reduction to [Cr(bpmp)] result in a high excited state redox potential. The ligand's methylene bridge acts as a Brønsted acid quenching the luminescence at high pH. Combined with a pH-insensitive chromium(III) emitter, ratiometric optical pH sensing is achieved with single wavelength excitation. The photophysical and ground state properties (quantum yield, lifetime, redox potential, and acid/base) of this spin-flip complex incorporating an earth-abundant metal surpass those of the classical precious metal [Ru(α-diimine)] charge transfer complexes, which are commonly employed in optical sensing and photo(redox) catalysis, underlining the bright future of these molecular ruby analogues.
在众多技术中，对光激发态的热力学和动力学实现化学控制对于高效且可持续地利用光活性过渡金属配合物至关重要。与由空间分离轨道描述的电荷转移态能量不同，自旋翻转态的能量不能直接预测，因为泡利排斥和电子云扩大效应起着关键作用。在多参考量子化学计算的指导下，我们报道了一种新型的高发光自旋翻转发射体，其具有量子化学预测的蓝移发光。铬配合物[Cr(bpmp)]（bpmp = 2,6 - 双(2 - 吡啶甲基)吡啶）的自旋翻转发射带从已知高发射性铬(III)配合物观察到的约780 nm移至更高能量的709 nm。光致发光量子产率攀升至20%，并且在室温下于酸性D₂O溶液中实现了毫秒级的非常长的激发态寿命。部分配体氘化将量子产率提高到25%。[Cr(bpmp)]的高激发态能量及其易于还原为[Cr(bpmp)]导致了高激发态氧化还原电位。配体的亚甲基桥在高pH下作为布朗斯特酸淬灭发光。与对pH不敏感的铬(III)发射体相结合，通过单波长激发实现了比率式光学pH传感。这种包含储量丰富金属的自旋翻转配合物的光物理和基态性质（量子产率、寿命、氧化还原电位和酸/碱）超过了经典的贵金属[Ru(α - 二亚胺)]电荷转移配合物，后者常用于光学传感和光（氧化还原）催化，凸显了这些分子红宝石类似物的光明前景。
