Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes [Ln 3 (H−HEDP) , and Y (QDU-1(Y)); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between Dy III ions and photogenerated O • radicals, showing SMM behavior after RT illumination. For the first time, we observed the reversible RT photochromism and photomagnetism in the lanthanide-based materials. This work realized the radicals-actuated on/off SMM behavior via RT light irradiation, providing a new strategy for constructing the lightinduced SMMs.

Using the pillar-layer strategy, two isomorphic crystalline coordination compounds with obvious photochromic and photomagnetic behaviors actuated by nonphotochromic ligands were synthesized.

Multiple switchable physical properties have been demonstrated in one single niccolite structural metal-organic framework, [(CH CH ) NH ][Fe Fe (HCOO) ] (1), including (i) a reversible ferroelastic phase transition triggered by freezing the disordered (CH CH ) NH cations, (ii) a thermally switchable dielectric constant transition accompanied by phase transition, and (iii) thermal and positive magnetic field driven magnetic poles reversal at low temperatures, attributed to different responses of the magnetization of Fe and Fe sublattices to external stimuli. More interestingly, the exchange anisotropy between the two sublattices can also give rise to tunable positive and negative exchange bias fields. Straightforwardly, such diverse demonstrations of bistability in one single material (depending on the specific tuning way) will provide extra freedom and flexibility for the design of switcher devices.

The cover picture shows the molecular structure of the helically extended angular [8]phenylene. An unprecedented cobalt-catalyzed triple cyclization of an appropriate nonayne was successful in assembling the largest crystallographically characterized helical phenylene (heliphene). Its properties are intriguing; the heliphene is unusually configurationally labile and has a strongly attenuated bathochromic increment in the UV spectrum, shielding of the terminal rings as a result of spatial overlap, and alternating ring-current intensities along the angular frame. The X-ray crystallographic data detail the helical and s ± p distortive features. Most surprisingly, the remarkable flexibility of the heliphene provided an unusually low barrier (DG = (À 4.5 8C) 13.4 AE 0.4 kcal mol À1 ) for enantiomerization. The 1 H NMR spectrum was consistent with the alternation of cyclohexatrienoid and aromatic character; the terminal rings are the most diatropic and the penultimate ones the least. Further details about this chiral polycyclic benzenoid hydrocarbon are described by K. P. C. Vollhardt, et al. on p 3227 ff.

No abstract