Kaul Nidhi, Asempa Eyram, Valdez-Moreira Juan A, Smith Jeremy M, Jakubikova Elena, Hammarström Leif
Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523, SE-75120 Uppsala, Sweden.
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States.
J Am Chem Soc. 2024 Sep 4;146(35):24619-24629. doi: 10.1021/jacs.4c08588. Epub 2024 Aug 6.
Detailed photophysical investigation of a Mn(IV)-carbene complex has revealed that excitation into its lowest-energy absorption band (∼500 nm) results in the formation of an energetic ligand-to-metal charge-transfer (LMCT) state with a lifetime of 15 ns. To the best of our knowledge, this is the longest lifetime reported for charge-transfer states of first-row-based transition metal complexes in solution, barring those based on Cu, with a d configuration. A so-called superoxidant, Mn(IV)-carbene exhibits an excited state potential typically only harnessed via excited states of reactive organic radical species. Furthermore, the long-lived excited state in this case is found to be a dark doublet, with its transition to the quartet ground state being spin-forbidden, a contrast to most first-row literature examples, and a possible cause of the long lifetime. Showcasing excited state properties which in some cases exceed those of complexes based on precious metals, these findings not only advance the library of earth-abundant photosensitizers but also shed general insight into the photophysics of d and related Mn complexes.
对一种锰（IV）-卡宾配合物进行的详细光物理研究表明，激发至其最低能量吸收带（约500纳米）会导致形成一种能量较高的配体到金属的电荷转移（LMCT）态，其寿命为15纳秒。据我们所知，这是溶液中基于第一排过渡金属配合物的电荷转移态所报道的最长寿命，不包括基于具有d构型的铜的那些配合物。一种所谓的超氧化物，锰（IV）-卡宾表现出一种激发态势能，通常仅通过反应性有机自由基物种的激发态来利用。此外，在这种情况下发现的长寿命激发态是一个暗双重态，其向四重基态的跃迁是自旋禁阻的，这与大多数第一排文献中的例子形成对比，也是寿命长的一个可能原因。这些发现展示了在某些情况下超过基于贵金属的配合物的激发态性质，不仅扩充了地球上储量丰富的光敏剂库，还为d和相关锰配合物的光物理提供了一般性见解。
