Thermo- and photo-driven crystalline molecular switches comprising pseudorotaxanes

Abstract

This thesis describes the thermo- and photo-driven molecular switches comprising ferrocene-containing pseudorotaxanes in the solid state. Chapter 1 presents an overview of supermolecular chemistry as well as the purpose of this project. Chapter 2 describes the reversible mechanical deformations of the single crystals of the pseudorotaxanes caused by a combination of temperature control and light-irradiation. Laser irradiation to the ferrocenyl group of the pseudorotaxane induces molecular structural changes in the crystals: it triggers a crystal-to-crystal thermal phase transition deforming the crystal shape at 124 oC; it causes rapid and reversible expansion of the crystal at room temperature. In addition, the local laser irradiation to a part of the single crystal enables selective transport of micro-particles. Chapter 3 describes the preparation and morphological studies of the thermally responsive pseudorotaxane films. The thin films of the pseudorotaxane molecule can be prepared on a glass or SiO2 substrates by a solution casting method, which affords the polycrystalline films without dissociation of the pseudorotaxane molecule. Obtained films are characterized by X-ray diffraction, differential scanning calorimetry (DSC), polarized optical microscopy, and grazing incident wide-angle X-ray scattering (GIWAXS) measurement with temperature control. The pseudorotaxane film on the substrate exhibits the reorganization of the molecule to give a large crystal face with 50-100 μm on heating, followed by the reversible solid-to-solid thermal phase transition on heating and cooling. GIWAXS analysis can conduce to the molecular alignment of the pseudorotaxane in the film; the pseudorotaxane adopts edge-on orientation, in which one-side of oligo-ethylene glycol group -(CH2CH2O)n- of the dibenzocrown ether molecule in the pseudorotaxane lies on the substrate, probably due to the molecule-surface interaction and formation of the bulky interlocked structure. Chapter 4 described the synthesis and characterization of a new pseudorotaxane composed of 4,4’,5,5’-tetrabromodibenzo[24]crown-8 ether as a ring molecule and ferrocene-containing ammonium cation as an axle molecules. The optical properties of the pseudorotaxane are observed and related to the molecular alignment in the single crystal state. Chapter 5 presents the conclusions of the project and gives forecast of this research. Finally chapter 6 presents the experimental conditions.