Abstract
In this thesis, molecular alignment of pseudorotaxanes in single crystal state and an optical anisotropy of the crystals are described. In Chapter 2, a series of new pseudorotaxanes having interlocked structure of dibenzo[24]crown-8 ether (DB24C8) or 4,4’,5,5’-tetrabromodibenzo[24]crown-8 ether (DB24C8-Br4) and axle molecules based on ammonium cation are synthesized changing substituents of tolyl and phenyl groups in the axle molecules. Pseudorotaxane structures are analyzed by X-ray single crystallography, which shows that the pseudorotaxanes are stabilized their supermolecular structures by following non-covalent interactions in solid state: (1) hydrogen bonds (N+-H…O and C-H…O) between the oxygen acceptor atoms of the DB24C8 or DB24C8-Br4 ring molecule and the hydrogen donor atoms of the cation’s NH2+ and CH2 groups, (2) pi-pi intramolecular interactions between aromatic part of ring molecules and tolyl or phenyl part of axle molecules, and (3) pi-pi intermolecular interactions between aromatic rings. These crystallographic data are used for discussion of optical properties of pseudorotaxane crystals. The crystals of pseudorotaxanes having pi-pi intramolecular interactions tend to show higher birefringence value. On the other hand, the pseudorotaxanes with C-H…pi intramolecular interactions instead of the pi-pi intramolecular interactions give lower birefringence value. Chapter 3 shows that [2]pseudorotaxanes composed of ferrocene-containing axle with DB24C8 act as a thermally-driven molecular switch in the single-crystal state. The pseudorotaxane structure can be altered reversibly in the single crystal state by thermal stimulation by observation of differential scanning calorimetry (DSC) and polarized optical microscope combined with hot stage. When the counter anion is replaced from PF6− to AsF6−, the pseudorotaxane molecule applies C-H…pi intramolecular interaction which does not show crystal-to-crystal phase-transition. Birefringence values of these crystals are measured changing composition ratios of the counter anions (PF6−/AsF6−). The pseudorotaxanes with higher PF6− compositions show higher birefringences due to well-aligned aromatic rings derived from pi-pi interactions, whereas those with higher AsF6− compositions exhibit lower birefringence because of less ordered C-H…pi interactions.