Photochromic species exhibit not only color change but variation of diverse physicochemical properties in the reversible manner. Photoswitchable magnetism, the so-called photomagnetism, may find potential applications in optical information storage and medical service. Polycyanometallate compounds, especially Prussian Blue analogues (PBAs), were thought to offer the most promising perspectives in this field and have received great attention.
Unfortunately, most PBAs exhibit photomagnetism below liquid nitrogen temperature and only very few samples around room temperature (RT). Therefore, it is of great scientific significance to develop Polycyanometallate compounds with both photochromism and photomagnetism at room temperature.
In 2003, we reported the synthesis and crystal structure of the cyanide-bridged 3d−4f heterobimetallic compound [NdIII(DMF)4(H2O)3(μ-CN)FeIII(CN)5]·H2O (NdFeDMF). Somewhat after, Einaga and Iversen found this compound and other similar 3d−4f heterobimetallic hexacyanoferrates showed surprisingly photomagnetism at temperature below 50 K However, the photoresponsive mechanisms for these compounds remain ambiguous.
The research team headed by Prof. GUO GuoCong and WANG Mingsheng at the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, realized, for the first time, the photochromism and photomagnetism of 3d−4f hexacyanoferrates at room temperature (RT) in [EuIII(18C6)(H2O)3]FeIII(CN)6·2H2O.
Photoinduced electron transfer (PET) from crown to Fe(III) yields long-lived charge-separated species at RT in air in the solid state. Upon irradiation by UV-vis light, the compound showed typical photochromism with color change from yellowish to orange. The orange sample could slowly decolor in dark condition or heat. After coloration, the χMT value at 300 K fell by 33.5%. This magnitude is much larger than that of NdFeDMF (<3%) reported by Iversen et al.
This work for the first time found the photochromism and photomagnetism of a 3d–4f hexacyanoferrates at room temperature (RT). This work not only successfully excavated a new type of photochromic material from the known compounds, but develops a new type of photoinduced valence tautomeric compounds with room-temperature photomagnetism. This finding has been published in J. Am. Chem. Soc. 2015, 137, 10882−10885（http://pubs.acs.org/doi/10.1021/jacs.5b05320）.
The work has received financial support from 973 program (2013CB933200), the NSF of China (21373225, 21221001, 21471149), the NSF of Fujian Province (2014J07003, 2014J01065), and Youth Innovation Promotion Association, CAS.
Previously, Prof. GUO’s group has made a series of progress in structural chemistry of the organic-inorganic hybrid photochromic material. (Angew. Chem. Int. Ed., 2007, 46, 3269、2008, 47, 3565、2008, 47, 4149、2012, 51, 3432、2014, 53, 9298、2014, 53, 11529；Chem. Commun., 2010, 46, 361, review).
Photoinduced electron-transfer progress and photomagnetism of [EuIII(18C6)(H2O)3]FeIII(CN)6·2H2O（Image by Prof. GUO’s group）
Contact:
Prof. GUO Guocong
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
Email: gcguo@fjirsm.ac.cn
