Photophysics of Cage/Guest Assemblies: Photoinduced Electron Transfer between a Coordination Cage Containing Osmium(II) Luminophores, and Electron-Deficient Bound Guests in the Central Cavity.
Photophysics of Cage/Guest Assemblies: Photoinduced Electron Transfer between a Coordination Cage Containing Osmium(II) Luminophores, and Electron-Deficient Bound Guests in the Central Cavity.
复制标题
DOI：
10.1021/acs.inorgchem.8b02860
复制
发表时间：
2019-01
影响因子：
4.6
通讯作者：
Jennifer S. Train;A. Wragg;Alexander J. Auty;A. J. Metherell;D. Chekulaev;Christopher G. P. Taylor;S. Argent;J. Weinstein;M. Ward
中科院分区：
文献类型：
--
作者：
Jennifer S. Train;A. Wragg;Alexander J. Auty;A. J. Metherell;D. Chekulaev;Christopher G. P. Taylor;S. Argent;J. Weinstein;M. Ward
合成了一个异金属八核配位笼[Os4Zn4（Lnap）12] X16（记作Os·Zn; X =高氯酸盐或氯化物）（Lnap是一个双齿桥联配体，含有两个吡唑基-吡啶螯合单元，中间被一个1，5-萘二基间隔基隔开）.位于立方体的八个顶点中的四个的{Os（NN）3} 2+单元具有长寿命的磷光3MLCT激发态，其是比[Ru（bipy）3] 2+更强的电子供体。Os·Zn的氯化物形式是水溶性的，在其中心空腔中与疏水性的电子受体有机客体1，2，4，5-四氰基苯、1，4-萘醌和1-硝基萘结合，结合常数在103 - 104 M-1之间，导致Os（II）单元产生的磷光猝灭。已确定的晶体结构的同构的Co 8笼内含有一个分子的1，2，4，5-四氰基苯作为一个客户的空腔内的结构。超快瞬态吸收测量表明，形成的电荷分离的Os（III）/客体·-状态所产生的笼到客体的光诱导电子转移;这种状态是在13 - 21 ps内形成，并在约的时间尺度上衰减。200磅在具有大结合常数的竞争客体（环十一烷酮）的存在下，其从笼腔中置换每个电子接受猝灭剂，不再观察到电荷分离状态。此外，具有相同电子接受物种的单核{Os（NN）3} 2+模型络合物的组合显示没有形成电荷分离的Os（III）/客体·-态的证据。这两个对照实验表明，{Os（NN）3} 2+发色团需要组装成笼状结构，以结合电子接受客人，并发生PET。这些结果有助于铺平道路，利用光活性配位笼作为主机的光氧化还原催化反应的结合客人。
A heterometallic octanuclear coordination cage [Os4Zn4(Lnap)12]X16 (denoted Os•Zn; X = perchlorate or chloride) has been prepared (Lnap is a bis-bidentate bridging ligand containing two pyrazolyl-pyridine chelating units separated by a 1,5-naphthalenediyl spacer group). The {Os(NN)3}2+ units located at four of the eight vertices of the cube have a long-lived, phosphorescent 3MLCT excited state which is a stronger electron donor than [Ru(bipy)3]2+. The chloride form of Os•Zn is water-soluble and binds in its central cavity the hydrophobic electron-accepting organic guests 1,2,4,5-tetracyanobenzene, 1,4-naphthoquinone and 1-nitronaphthalene, with binding constants in the range 103-104 M-1, resulting in quenching of the phosphorescence arising from the Os(II) units. A crystal structure of an isostructural Co8 cage containing one molecule of 1,2,4,5-tetracyanobenzene as a guest inside the cavity has been determined. Ultrafast transient absorption measurements show formation of a charge-separated Os(III)/guest•- state arising from cage-to-guest photoinduced electron transfer; this state is formed within 13-21 ps, and decays on a time scale of ca. 200 ps. In the presence of a competing guest with a large binding constant (cycloundecanone) which displaces each electron-accepting quencher from the cage cavity, the charge-separated state is no longer observed. Further, a combination of mononuclear {Os(NN)3}2+ model complexes with the same electron-accepting species showed no evidence for formation of charge-separated Os(III)/guest•- states. These two control experiments indicate that the {Os(NN)3}2+ chromophores need to be assembled into the cage structure to bind the electron-accepting guests, and for PET to occur. These results help to pave the way for use of photoactive coordination cages as hosts for photoredox catalysis reactions on bound guests.