Successful control of the orientation of the π-electron systems in media has been achieved in certain liquid crystals, making them applicable to devices for optical systems because of the variation in the optical properties with the orientation of the π-electron system. However, because of close packing, changing the orientation of molecules in the crystalline state is usually difficult. A macrocage molecule with a bridged thiophene rotor was synthesized as a molecular gyrotop having a dipolar rotor, given that the dipole derived from the thiophene can rotate even in the crystal. The thermally induced change in the orientation of the dipolar rotors (thiophene ring) inside the crystal, i.e., order-disorder transition, and the variation in the optical properties in the crystalline state were observed.

Recently, functional organic materials have been put into practical use. The application of molecular motions has the potential to create new molecule-based materials. For this reason, considerable attention has been focused on the chemistry and properties of molecular machines in which mechanical motions of parts of the molecules are observed. In particular, phenylene rotation in the crystalline state has been investigated using framed molecular gyrotops having a phenylene rotor encased in three long alkyl spokes. In this study, we show thermal modulation of birefringence in a crystal due to the states of dynamic equilibrium of a novel molecular gyrotop. A macrocage molecule having a bridged phenylene rotor was synthesized as a novel molecular gyrotop. Rapid rotation of the phenylene rotor of the molecular gyrotop was confirmed by solid-state 2 H NMR spectroscopy that showed changes in the optical properties of a single crystal, i.e., the thermal modulation of birefringence. These results are the first application of the dynamic states in a crystal causing an optical change. These phenomena were also confirmed by control experiments using a molecular gyrotop with a nonrotating xylene rotor. We anticipate our finding to be a starting point for the creation of a new field of material chemistry that will make use of the dynamic states of molecules. molecular design | molecular material | solid-state NMR O rganic materials, such as liquid crystals and organic lightemitting devices, have been put into practical use, and they have improved the lifestyles of people. These functional organic molecules usually contain moieties of planar π-electron systems such as benzene and naphthalene (1). Benzene is one of the simplest aromatic molecules, and due to its planar structure, a strong anisotropy exists in its physical properties between the in-plane and out-of-plane directions. Therefore, an aggregate of oriented π-electron systems such as crystals and liquid crystals shows anisotropy in its physical properties. When the orientation of molecules inside an ordered aggregation can be switched by partial molecular motion, the physical properties may switch between being anisotropic and isotropic, or they may change the direction of anisotropy as observed in the study of functional liquid crystals and so on. In other words, the application of molecular motions inside an ordered aggregate has the potential to create new molecule-based materials. For this reason, considerable attention has been focused on the chemistry of molecular machines (2-9) in which mechanical motions of parts of the molecules are observed. In particular, the chemistry of partial molecular rotations in the crystalline state has been investigated using molecules that consist of rotors and stators (2,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Macrocyclic molecules having a rotor encased in a three-spoke stator are expected to have the functions of gyroscopes and compasses in the crystalline state; such molecules were reported as molecular g...

Introduction of the clutch-declutch mechanism into a new gear system, bis(4-methyl-9-triptycyl)difluorosilane 1, is achieved by the reversible attachment of fluoride ion giving the corresponding fluorosilicate 2. Although the phase isomers of 1 (1(dl) and 1(meso)) cannot be separated because of the equilibrium via a slow gear slippage process (DeltaH(double dagger) = 17.2 +/- 0.2 kcal x mol(-1) and DeltaS(double dagger) = 0.9 +/- 0.9 cal x mol(-1) x K(-1)), 1 works as meshed molecular gears in solution at room temperature. On the other hand, silicate 2 in the solid state has quite an unusual TBP structure having two organic triptycyl groups at the apical positions and three electronegative fluorine atoms at the equatorial positions against the Muetterties rule. Rotation of the two triptycyl groups around Si-C bonds in 2 is facile and independent to each other in solution. Silicate 2 is reverted to the corresponding silane mixture by treating with excess water.

Photolysis of diazomethylstannylene 2 (ArSn-C(N2)Si(i-Pr)3, Ar = C6H3-2,6-Tip2 (Tip = C6H2-2,4,6-(i-Pr)3)) generated formal stannaacetylene 1 as a reactive intermediate, which was evidenced by the formation of cyclic arylalkylstannylene 4 via an intramolecular carbene insertion to a CH bond of isopropyl groups. The structures of the compounds 2 and 4 were fully characterized by X-ray crystallography. Stannaacetylene 1 was directly observed by laser flash photolysis of 2; lambdamax = 355 nm, tau = 50 ms at room temperature. No triplet ESR signals were observed during the photolysis of 2 in 3-methylpentane glass matrix at 77 K, indicating the singlet nature of 1. Theoretical calculations for the parent stannaacetylene suggest that the stannaacetylene is characterized as a SnC triple-bonded compound with a significant contribution of stannylene-(doubly excited)carbene structure.

Significant electron-donating effects of the germyl substituents in the first stable monomeric germyl-(aryl)stannylene and germyl(aryl)germylene, which have the sterically encumbering 2,6-dimesitylphenyl group as the aryl substituent, were evidenced by the n f p transition bands appearing at very long wavelengths and the significant downfield shift of the 119 Sn NMR resonance in the stannylene.

A macrocage molecule with a bridged phenylene rotor has been reported as a molecular gyrotop, because the rotor can rotate even in a crystalline state. Although the most stable cage structure of the molecular gyrotop in a crystal was folded and shrunken at low temperature, expansion of the cage was observed at high temperature due to rapid rotation of the phenylene in a crystal. This phenomenon is analogous to the deflation and inflation of a balloon. Moreover, the unusually large thermal expansion coefficient of the crystal was estimated in the temperature range in which the expansion of the cage was observed, indicating a new function of dynamic states of the molecules.

A molecular gyroscope which has a phenylene rotator encased in three long siloxaalkane spokes was synthesized. The phenylene ring is observed by X-ray crystallography at three rotational positions around the 1,4-axis between 223–303 K. The area in which the phenylene ring is found is significantly reduced at 173 K owing to the deformation of a siloxaalkane spoke; the temperature-dependent phenylene disorder is reversible.

Macrocage molecules with a bridged π-electron system have been reported as molecular gyrotops in which the π-electron system can rotate within the cage. We recently reported the dynamics of the rotor in solution using 1,4-naphthalenediyl-bridged molecular gyrotops, which consist of cages formed of three C14, C16, or C18 chains. In this work, we synthesized novel gyrotops with C15 and C17 chains and systematically investigated the activation energies for the rotation of the rotor in solution. The activation energies for rotation in solution were found to decrease with increasing size of the cage. Therefore, a rotational barrier can be designed by adjusting the length of the side chains in these molecular gyrotops. Additionally, these gyrotops were fluorescent in solution; the quantum yields and lifetimes of the fluorescence were investigated. However, these properties were not influenced by the chain length owing to a large difference in time scale between fluorescence (10(-8)-10(-9) s) and the rotational dynamics inside the cage (10°-10(-5) s).