Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States.
Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States.
J Am Chem Soc. 2018 Apr 18;140(15):5161-5170. doi: 10.1021/jacs.8b00599. Epub 2018 Apr 4.
A series of dirhodium(II,II) paddlewheeel complexes of the type cis-[Rh(μ-DTolF)(μ-L)][BF], where DTolF = N,N'-di( p-tolyl)formamidinate and L = 1,8-naphthyridine (np), 2-(pyridin-2-yl)-1,8-naphthyridine (pynp), 2-(quinolin-2-yl)-1,8-naphthyridine (qnnp), and 2-(1,8-naphthyridin-2-yl)quinoxaline (qxnp), were synthesized and characterized. These molecules feature new tridentate ligands that concomitantly bridge the dirhodium core and cap the axial positions. The complexes absorb light strongly throughout the ultraviolet/visible range and into the near-infrared region and exhibit relatively long-lived triplet excited-state lifetimes. Both the singlet and triplet excited states exhibit metal/ligand-to-ligand charge transfer (ML-LCT) in nature as determined by transient absorption spectroscopy and spectroelectrochemistry measurements. When irradiated with low-energy light, these black dyes are capable of undergoing reversible bimolecular electron transfer both to the electron acceptor methyl viologen and from the electron donor p-phenylenediamine. Photoinduced charge transfer in the latter was inaccessible with previous Rh(II,II) complexes. These results underscore the fact that the excited state of this class of molecules can be readily tuned for electron-transfer reactions upon simple synthetic modification and highlight their potential as excellent candidates for p- and n-type semiconductor applications and for improved harvesting of low-energy light to drive useful photochemical reactions.
一系列顺式-[Rh(μ-DTolF)(μ-L)][BF]的二钌(II,II)桨轮配合物，其中 DTolF = N,N'-二(对甲苯基)甲脒基和 L = 1,8-萘啶（np）、2-(吡啶-2-基)-1,8-萘啶（pynp）、2-(喹啉-2-基)-1,8-萘啶（qnnp）和 2-(1,8-萘啶-2-基)喹喔啉（qxnp），被合成并进行了表征。这些分子具有新的三齿配体，同时桥接二钌核心并覆盖轴向位置。这些配合物在整个紫外线/可见光谱范围内和近红外区域强烈吸收光，并表现出相对较长的三重态激发态寿命。通过瞬态吸收光谱和光谱电化学测量确定，单重态和三重态激发态均具有金属/配体-配体电荷转移（ML-LCT）性质。当用低能量光照射时，这些黑色染料能够可逆地经历双分子电子转移，分别向电子受体甲基紫精和电子供体对苯二胺。以前的 Rh(II,II)配合物无法进行后者的光致电荷转移。这些结果强调了这样一个事实，即通过简单的合成修饰，此类分子的激发态可以很容易地为电子转移反应进行调整，并突出了它们作为 p 型和 n 型半导体应用以及改善低能量光收集以驱动有用光化学反应的优秀候选物的潜力。
