Abstract
In this thesis, photoinduced mechanical motions and photochemical reactions of supramolecular materials are described. In chapter 2, crystalline phase transitions caused by external stimuli have been used to detect physical changes in the solid state properties. This study presents the mechanical switching of crystals of ferrocene-containing pseudorotaxane controlled by focused laser light. The expansion and contraction of the crystals can be driven by turning on and off laser light at 445 nm. The irradiation-induced expansion of the crystal involves elongation along the a, b and c axes at 30 °C, whereas heating of the crystal at 105 °C causes the shortening of c axis. The expansions reversibly occur and have the advantage of a rapid relaxation (reverse) process. Single-crystal X-ray crystallography reveals the detailed structural changes of the molecules, corresponding to a change in the size of the crystals upon laser irradiation. This molecular crystal behavior induced by laser irradiation, is demonstrated for the remote control of objects, namely, microparticle transport and microswitching in an electric circuit. In Chapter 3, molecular machines and switches composed of flexible pseudorotaxanes respond to external stimuli, transducing incident energy into mechanical motions. This study presents thermo- and photoresponsive dynamic pseudorotaxane crystals composed of axle molecules containing ferrocene or ruthenocene groups threaded through dibenzo[24]crown-8 ether rings. The ruthenocene-containing pseudorotaxane exhibits a crystal-to-crystal thermal phase transition at 86 °C, which is much lower than that of the ferrocene-containing pseudorotaxane (128 °C). Single crystal X-ray crystallography at various temperatures reveals the details of the structural changes, and shows that the bulky ruthenocene provides distortion in the pseudorotaxane structure to facilitate twisting of the axle molecule. A mixed ferrocene and ruthenocene pseudorotaxane crystal is applied to photomechanical conversion under 405 nm laser irradiation at 85 °C and provides a lifting force 6,400-times the weight of the crystal itself upon phase transition. In Chapter 4, photoresponsive dynamic pseudorotaxane crystals composed of axle molecules containing biferrocene or ferrocene groups threaded through a dibenzo[24]crown-8 ether ring are described. A biferrocene-containing pseudorotaxane crystal is used for photomechanical conversion under 445-nm laser irradiation and provides a lifting force that is 2900-times the weight of the crystal itself. In Chapter 5, synthesis, crystal packing, photo- and thermallyinduced reactions of various pseudorotaxane crystals are described. Ferrocenylmethylamine-based pseudorotaxane crystal (5-1H) and its tolyl, phenyl, ethyl and methyl derivatives composed of axle and dibenzo[24]crown-8 ether (DB24C8) ring molecule (1, 5-1Phe, 5-1Eth and 5-1Me) or a tetrabromo-substituted DB24C8-Br4 ring molecule (5-2Tol, 5-2Phe, 5-2Eth, 5-2Me and 5-2H) or a smaller DB18C6 ring molecule (5-3Me and 5-3H) are compared to explore the effect that a structurally modification can have on the photo- and thermallyinduced reactivity. The structure of the derivatives were determined using single-crystal X-ray crystallography. Efficient photoinduced mechanical motion can be achieved by pseudorotaxane with shorter axle molecules, which has a higher photosensitivity at 445 nm (The expansion ratio induced by 445 nm laser: 5-1H > 5-1Me > 5-1Eth > 5-1Phe > 1). In addition, the polymorphous crystals of 5-1H and 5-3Me have different thermal phase transition temperature observed via differential scanning calorimetry (DSC). In Chapter 6, we investigated the dynamic photoresponse of crystals with stilbene and ferrocenyl groups. Single-crystal X-ray crystallography of the molecules shows that only neutral crystal and a crystal with a Cl- group as counter anion exhibit central-to-central π-π interaction between two aromatic rings in which this alignment would be disturbed by exchanging the counter anions to BF4- and PF6-. The [2 + 2] cycloaddition reaction induced by 355 nm UV irradiation was discussed in both solid and solution state. After UV irradiation to a solution of [(FcMAS)·H]+(Cl)- in DMSO-d6, 1H NMR spectrum shows peaks corresponding to the cyclobutane group. The expansion and contraction of crystals induced by 445 nm laser irradiation is compared to ferrocene containing pseudorotaxane crystal. The photo-mechanical conversion efficiency is over 1.7 times higher than our previous results. Moreover, these crystals show interesting secondary harmonic generation (SHG) phenomenon induced by 1030 nm femtosecond laser irradiation, and the frequency is doubled to 515 nm via these crystals. In Chapter 7, facile photoresponsive actuators comprising of ferrocene as a guest chromophore and poly(butyl methacrylate) (PBMA) as a host matrix are described. The ferrocene-doped PBMA film shows mechanical expansion and contraction by turning on and off a 445-nm laser. The photoresponsive film is attached with a commercial sticky tape composed of acetylcellulose, exhibiting a bending motions controlled by turning on and off the laser. The double-layer film is applied to fabricate a table-shaped lifting machine (0.7 mg), lifting a 10.5 mg object up and down by turning on and off the laser. The mechanical force provided by the double-layer film is also recorded. Furthermore, the film with gold-coating is applied to an electric circuit, serving as reversible photoresponsive switch. This film preparation technique is applied to other chromophores (e.g. coumarin 343, rhodamine 6G, sudan blue II and solvent green 3) to control motion of the films independently using 445-nm, 520-nm and 655-nm lasers. The ferrocene-doped films show photoinduced healing from mechanical damages. Finally, morphology changes in the film accompanied by the photoirradiation are observed by the small angle X-ray scattering technique. In Chapter 8, experimental methods are described. In Chapter 9, some suggestions for future prospect are described.