Masakazu Morimoto

A diarylethene cocrystal that converts light into mechanical work.

The photomechancial effect of a rectangular plate two-component cocrystal composed of a photochromic diarylethene derivative, 1,2-bis(2-methyl-5-(1-naphthyl)-3-thienyl)perfluorocyclopentene (1o), and perfluoronaphthalene (FN) has been examined. The crystal of 1o·FN with the size of 1-5 mm in length exhibits reversible bending motion upon alternate irradiation with ultraviolet (UV) and visible light. The reversible bending could be repeated over 250 times. In situ X-ray crystallographic analysis revealed that the deformation of the crystal is due to the elongation of the b-axis of the unit cell, which corresponds to the long axis of the plate crystal, induced by the shape change of component diarylethene molecules upon photocyclization. The bending motion was observed even at 4.7 K, and dynamic measurement of the bending proved that the anisotropic expansion of the crystal takes place in the microsecond time scale at the low temperature. Molecular crystal cantilevers made of 1o·FN can lift metal balls, the weight of which is 200-600 times heavier than the weight of the crystal, upon UV irradiation. The maximum stress generated by UV irradiation was estimated to be 44 MPa, which is 100 times larger than that of muscles (∼0.3 MPa) and comparable to that of piezoelectric crystals, such as lead zirconate titanate (PZT) (∼50 MPa).

Light‐Driven Molecular‐Crystal Actuators: Rapid and Reversible Bending of Rodlike Mixed Crystals of Diarylethene Derivatives

Piezoelectric crystals are useful in industrial and consumer applications because of their special characteristics: they can be bent by electricity. But the crystals require a wire connection so that the electricity can be supplied. This wire connection prevents their use in water and reduction of their size to the micrometer scale. Herein, we report on wireless molecular-crystal actuators, which work upon photoirradiation. Rodlike mixed crystals of 1-(5-methyl-2-phenyl-4-thiazolyl)-2-(5-methyl-2-p-tolyl-4-thiazolyl)perfluorocyclopentene (1a) and 1,2-(5-methyl-2-p-tolyl-4-thiazolyl)perfluorocyclopentene (2a ; Scheme 1) with sizes ranging from micro-

Coordination Assemblies of [Mn4] Single-Molecule Magnets Linked by Photochromic Ligands: Photochemical Control of the Magnetic Properties

To achieve reversible photoswitching of the magnetic properties of single-molecule magnets (SMMs), coordination assemblies of a mixed valence tetranuclear [Mn(II)(2)Mn(III)(2)] complex linked by open- and closed-ring isomers of a photochromic diarylethene ligand were synthesized: [Mn(4)(hmp)(6)(dae-o)(2)(ClO(4))(2)] x 6 H(2)O (open-ring form; 1o) and [Mn(4)(hmp)(6)(dae-c)(2)(H(2)O)(2)](ClO(4))(2) x CH(3)CN x 4 H(2)O (closed-ring form; 1c), where Hhmp is 2-hydroxymethylpyridine, and H(2)dae-o and H(2)dae-c are open- and closed-ring isomers of 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H(2)dae), respectively. From X-ray crystallographic analyses, 1o and 1c have one-dimensional (1-D) chain structures with a repeating unit of [-{Mn(4)}-(dae)-], in which the [Mn(4)] units are bridged by the diarylethene ligands coordinated to the Mn(II) sites via carboxylate groups. Magnetic measurements involving direct-current (dc) and alternating-current (ac) techniques showed that each [Mn(4)] cluster in the 1-D chains had an S(T) = 9 ground state due to two kinds of intracluster ferromagnetic exchange interactions and behaved as SMMs. Both 1o and 1c underwent photochromic reactions in the crystalline phase, and their colors reversibly changed between reddish-brown and blue upon irradiation with ultraviolet (UV) and visible light. For 1o, no significant change in the magnetic properties was observed after the photocyclization of the dae-o moiety by UV irradiation. In contrast, the photocycloreversion of the dae-c moiety by visible irradiation enhanced inter-[Mn(4)] unit interactions in 1c, which was triggered by the geometrical change in the diarylethene moiety during the photoreaction and the subsequent change in the inter-[Mn(4)] arrangement between the neighboring 1-D chains. This work illustrates the usefulness of photochromic molecules for photoswitching the magnetic behavior of complexes, even superparamagnetic systems, with SMM units.

Photochromism of diarylethene single crystals: crystal structures and photochromic performance

Diarylethenes undergo thermally irreversible and fatigue-resistant photochromic reactions not only in solution but also in the single-crystalline phase. This article describes recent development of the single-crystalline photochromism of diarylethene derivatives. We focused on the relationship between their crystal structures and the photochromic performance. Photocyclization/cycloreversion quantum yields, absorption spectra, the absorption anisotropies, and surface morphology changes are strongly dependent on the conformations and packing structures of the molecules in the crystals.

Copper(II)-terbium(III) Single-Molecule Magnets linked by photochromic ligands

Two assemblies composed of single-molecule magnets (SMMs) linked by photochromic ligands, [Cu(II)(2)Tb(III)(2)(L)(2)(NO(3))(2)(dae-o)(2)]·2(n-BuOH) (1) and {[Cu(II)Tb(III)(L)(n-BuOH)(0.5)](2)(dae-c)(3)}·5(DMF)·4(n-BuOH)·2(H(2)O) (2), were synthesized by reacting the SMM [Cu(II)Tb(III)(L)(NO(3))(3)] (H(2)L = 1,3-bis((3-methoxysalicylidene)amino)propane) and photochromic molecules, H(2)dae-o and H(2)dae-c, which are open- and closed-ring isomers of 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluoropentene (H(2)dae), respectively. 1 has a tetranuclear ring-like structure comprised of two [CuTb] units and two dae-o(2-) ligands. On the other hand, 2 has a one-dimensional ladder-type structure involving the [CuTb] and dae-c(2-) units in a 3 : 2 ratio. Magnetic studies revealed that 1 and 2 had ferromagnetic interactions between the Cu(II) and Tb(III) ions and that both compounds exhibited frequency dependence of ac susceptibilities owing to freezing the magnetization of the [CuTb] SMM. Upon irradiation with ultraviolet light and visible light, an absorption band at ∼600 nm changed, indicating that photochromic reactions involving the dae(2-) ligands occurred. After irradiation, the magnetic behaviour of 1 did not change, whereas magnetic behaviour of 2 changed, due to the modification of intermolecular environment.

Photocontrol Over Self‐Assembled Nanostructures of π–π Stacked Dyes Supported by the Parallel Conformer of Diarylethene

Diarylethenes (DAEs) have rarely been used in the design of photoresponsive supramolecular assemblies with a well-defined morphology transition owing to rather small structural changes upon photoisomerization. A supramolecular design based on the parallel conformation of DAEs enables the construction of photoresponsive dye assemblies that undergo remarkable nanomorphology transitions. The cooperative stacking of perylene bisimide (PBI) dyes was used to stabilize the parallel conformer of DAE through complementary hydrogen bonds. Atomic force microscopy, UV/Vis spectroscopy, and molecular modeling revealed that our DAE and PBI building blocks coassembled in nonpolar solvent to form well-defined helical nanofibers featuring J-type dimers of PBI dyes. Upon irradiating the coassembly solution with UV and visible light in turn, a reversible morphology change between nanofibers and nanoparticles was observed. This system involves the generation of a new self-assembly pathway by means of photocontrol.

Reversible Photocontrol of Surface Wettability between Hydrophilic and Superhydrophobic Surfaces on an Asymmetric Diarylethene Solid Surface

By alternate UV and visible light irradiation, reversible topographical changes were observed on a newly synthesized diarylethene microcrystalline surface between the rough crystalline surface of an open-ring isomer and flat eutectic surfaces. The contact angle changes of a water droplet between 80° and 150° and peak intensities changes of the open-ring isomer in XRD patterns within 2 h of repeating cycle were observed. The results indicated that reversibly photogenerated rod-shaped crystals on the surface were produced based on the lattice of the open-ring isomer crystals in the subphase.

Control of the single-molecule magnet behavior of lanthanide-diarylethene photochromic assemblies by irradiation with light.

Lanthanide-based extended coordination frameworks showing photocontrolled single-molecule magnet (SMM) behavior were prepared by combining highly anisotropic Dy(III) and Ho(III) ions with the carboxylato-functionalized photochromic molecule 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H2 dae), which acts as a bridging ligand. As a result, two new compounds of the general formula [{Ln(III) 2 (dae)3 (DMSO)3 (MeOH)}⋅10 MeOH]n (M=Dy for 1 a and Ho for 2) and two additional pseudo-polymorphs [{Dy(III) 2 (dae)3 (DMSO)3 (H2 O)}⋅x MeOH]n (1 b) and [{Dy(III) 2 (dae)3 (DMSO)3 (DMSO)}⋅x MeOH]n (1 c) were obtained. All four compounds have 2D coordination-layer topologies, in which carboxylate-bridged Ln2 units are linked together by dae(2-) anions into grid-like frameworks. All four compounds exhibited a strong reversible photochromic response to UV/Vis light. Moreover, both 1 a and 2 show field-induced SMM behavior. The slow magnetic relaxation of 1 a is influenced by the photoisomerization reaction leading to the observation of the cross-effect: photocontrolled SMM behavior.

Photoreversible Supramolecular Polymerisation and Hierarchical Organization of Hydrogen‐Bonded Supramolecular Co‐polymers Composed of Diarylethenes and Oligothiophenes

Diarylethene 1 equipped with two monotopic melamine hydrogen-bonding sites and oligothiophene-functionalized ditopic cyanurate (OTCA) were mixed in a nonpolar solvent to form AA-BB-type supramolecular co-polymers (SCPs) bearing photoswitchable moieties in their main chains and extended π systems as side chains. UV/Vis, fluorescence, dynamic light scattering (DLS), TEM, and AFM studies revealed that the two functional co-monomers formed flexible quasi-one-dimensional SCPs in solution that hierarchically self-organized into helical nanofibers through H-aggregation of the oligothiophene side chains. Upon irradiating the SCPs with UV light, a transition occurred from the H-aggregated state to non-aggregated monomeric oligothiophene side chains, as shown by spectroscopic studies, which indicates the formation of small oligomeric species held together only by hydrogen-bonding interactions. TEM and AFM visualized unfolded fibrils corresponding to elongated single SCP chains formed upon removal of solvent. The helical nanofibers were regenerated upon irradiating the UV-irradiated solution with visible light. These results demonstrated that the supramolecular polymerisation followed by hierarchical organization can be effectively controlled by proper supramolecular designs using diarylethenes and π-conjugated oligomers.

Absolute asymmetric photocyclization in chiral diarylethene co-crystals with octafluoronaphthalene

A photochromic diarylethene containing naphthyl groups formed a chiral crystal when co-crystallized with octafluoronaphthalene, although both molecules are achiral, and underwent highly enantioselective photocyclization owing to the conformational confinement in the crystal.