Molecular Gyrotops Research Articles

Theoretical Investigations of the Crystal Structures and Molecular Energetics of High Quality Silicon Carbide (β-SiC) Precursor Compound 1,4-bis(trimethylsilyl)benzene

Over the last decades, the rapidly growing theoretical methods have revolutionized whole scientific paradigm, developed state-of-art analyses, and created substantial computational platforms through the huge support of outstanding mathematical algorithms. The self-consistent-charge density-functional based tight-binding (SCC-DFTB) scheme is one of them that offers versatile and efficient quantum mechanical calculations with some unique features compatible especially to the crystalline solid even at low computational resources. Its effective parametrizations and computational implementations under the Gaussian standardized interface as an "External program" via the users' script (Gaussian- External methodology; GEM) has added an additional value because of which various in-built high-level Gaussian computations are directly accessible. Herewith, the Gaussian offered geometry optimization algorithms and convergence criteria plus the ModRedundant type relaxed potential energy surface (PES) scanning techniques are assessed through the GEM, and characterized the crystal structures with concerned molecular energetics and PES of the experimentally synthesized 1,4-bis (trimethylsilyl) benzene (1,4-BTMSB) compound; a potential precursor for the high quality Silicon Carbide (β-SiC) coating particles, and an ideal "Internal Standard" for the quantitative spectroscopic analyses. The general results reveal that the 1,4- BTMSB molecules in its unit-cell and crystal lattice experience significant non-bonding interactions that induces them to attain the definite molecular geometry with recognizable ring, angle, torsional, and steric strains. The quantitative analyses of its PES depict that the phenylene ring has to overcome multiple yet unidentical energy barriers with the tallest Ea1= 5.3 kcal/mol in order to undergo internal 2π angular rotation around the 1,4-(C-Si) axes. And, exhibiting such type internal rotation of its phenylene ring is energetically highly probable as this compound is widely employed in coating high temperature reactors, and in quantizing analyte in high energy run spectroscopic facilities. The same quantification is referred here in order to underscore the significance of adopting perfectly closed topological molecular architectures while designing/synthesizing amphidynamic type crystalline free molecular gyrotops and their prototypes.

Synthesis and fluorescence properties of 9,9-dimethylfluorene-diyl bridged molecular gyrotops: effects of slight fluorophore motion on fluorescence efficiency in the solid state

Solid-state fluorescence was quenched by libration of a fluorophore in a dimethylfluorene-diyl bridged macrocage.

Structure and Dynamics of Crystalline Molecular Gyrotops with a Difluorophenylene Rotor.

Macrocage molecules with a bridged π-electron system could be assumed as crystalline molecular gyrotops because of the structural similarity and the rotatable π-electron system. In this study, 1,2-difluoro-3,6-phenylene-bridged macrocages were designed and synthesized as crystalline molecular gyrotops with a dipolar rotor. The thermal ring dynamics of the dipolar rotor in the crystal were investigated by solid-state NMR and dielectric spectroscopy. The gyrotop that was surrounded by three C14-alkyl chains exhibited an exchange between two stationary positions in the crystalline state. In contrast, the gyrotop cage consisting of C18 chains exhibited no dynamics in the crystalline state. Although the corresponding phenylene derivatives exhibit a facile rotational motion of the phenylene group in the crystalline state, the dynamics of each derivative was observed to be different. The reason for this difference is ascribed to the difference in the bulkiness between the fluorine and hydrogen atoms in the rotor.

A Furan-2,5-diyl Bridged Macrocage as a Highly Distorted Molecular Gyrotop

A novel molecular gyrotop with a furan-2,5-diyl was synthesized. The furan-diyl rotor showed rotation inside the cage in a solution. However, no furan-rotor dynamics was observed in a crystalline s...

Chemistry of Macrocage Molecules with a Bridged π-Electron System as Crystalline Molecular Gyrotops

Rotation of the part of the molecules has been of interest in terms of artificial molecular rotors, which are one of the classes of molecular machines. We have been investigated macrocage molecules with a bridged π-electron system have been synthesized as “crystalline molecular gyrotops”, because the interior π-electron system can be rotate even in a crystal. These molecules were easily synthesized by applying silicon junctions that connect the π-electron rotor and three alkyl spokes. In this paper, chemistry of molecular gyrotops having phenylene, biphenylene, naphthalene-diyl, thiophene-diyl, and thiophenedioxide-diyl rotors have been described. Their cage structures were successfully confirmed by X-ray crystallography. Rotation of the rotor was investigated by solution and solid-state NMR spectroscopy. Some of them showed crystal-to-crystal phase transitions between static and dynamic states of the rotor, and their mechanisms were discussed.

Dielectric Relaxation of Powdered Molecular Gyrotops Having a Thiophene Dioxide-diyl as a Dipolar Rotor

The dielectric properties of powdered molecular gyrotops with a thiophenedioxide-diyl are reported. Crystals without a solvent molecule show usual dielectric relaxation spectra due to orientation polarization of the dipolar rotor, while a crystal having ethanol as the crystalline solvent molecule showed novel temperature-dependent dielectric relaxation switching by crystal-to-crystal phase transition, which is induced by hydrogen-bonding interactions between thiophene dioxide and ethanol.

A crystalline molecular gyrotop with a biphenylene dirotor and its temperature-dependent birefringence

A crystalline molecular gyrotop with a biphenylene dirotor showed a reduction in the birefringence with increasing temperature.

Molecular Gyrotops with a Five-Membered Heteroaromatic Ring: Synthesis, Temperature-Dependent Orientation of Dipolar Rotors inside the Crystal, and its Birefringence Change

Three-dimensional arrays of dipolar rotors were constructed as single crystals of molecular gyrotops, which are macrocage molecules with a bridged dipolar rotor. In this study, we synthesized novel molecular gyrotops with a five-membered heteroring, i.e., furan-diyl (1), thiophene-diyl (2), and selenophene-diyl (3), and investigated the temperature-dependent orientation and rotation of the dipolar rotors inside the crystal. Unfortunately, furan derivative 1 did not crystallize; however, crystal structures of the other molecular gyrotops, i.e., 2 and 3, showed three-dimensional arrays of dipolar rotors. Thermal order–disorder transitions of the dipolar rotor orientation inside the crystal were observed in 2 and 3 with the transition temperature in selenophene derivative 3 being lower than that of thiophene derivative 2. This may be ascribed to subtle differences in the molecular structure, e.g., the intersection angle between two Si–C(aryl) bonds corresponding to the rotation axis. In accordance with the t...

1,4-Naphthalenediyl-Bridged Molecular Gyrotops: Rotation of the Rotor and Fluorescence in Solution.

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).

Synthesis of crystalline molecular gyrotops and phenylene rotation inside the cage.

Phenylene-bridged macrocage molecules were synthesized as molecular gyrotops because the rotor can rotate even in a crystal. The chain-length-dependent properties of the molecular gyrotops were investigated in order to explore the potential to create new molecular materials. The formation of the cage in the synthesis of each molecular gyrotop depended on the length of the alkyl chains of the precursor. The rotation modes and energy barriers for phenylene rotation inside the crystals of the molecular gyrotops were changed by varying the chain length of the cage.

Ring-closing metathesis for the synthesis of a molecular gyrotop.

Macrocage molecules with a bridged phenylene rotor have been synthesized as molecular gyrotops, whose cages were constructed by ring-closing metathesis (RCM) of bis(trialkenylsilyl)benzenes. An analysis of the yields of the products in the RCM reaction under various temperature conditions revealed that the desired cage, i.e., a molecular gyrotop, was produced in good yield under reflux, indicating that the cage is a thermodynamically controlled product.

A crystalline molecular gyrotop with germanium junctions between a phenylene rotor and alkyl spokes

A molecular gyrotop with germanium junctions was synthesized, and the dynamics of the phenylene and the optical properties were discussed.

Order–Disorder Transition of Dipolar Rotor in a Crystalline Molecular Gyrotop and Its Optical Change

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.

Cage Size Effects on the Rotation of Molecular Gyrotops with 1,4-Naphthalenediyl Rotor in Solution

1,4-Naphthalenediyl-bridged macrocages (2, 3, and 4) were synthesized as novel molecular gyrotops. Compound 2 (C14 chains) does not show rotation of the naphthalene ring about an axis in solution. The 1,4-naphthalenediyl moieties of compounds 3 (C16 chains) and 4 (C18 chains) show restricted and rapid rotation inside the cage in solution, respectively. Therefore, steric protective effects on the rotation of the rotor in molecular gyrotops can be controlled by changing the size of the cage.

A Molecular Balloon: Expansion of a Molecular Gyrotop Cage Due to Rotation of the Phenylene Rotor

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.

Thermal modulation of birefringence observed in a crystalline molecular gyrotop

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.

結晶中でπ電子系が回転する「分子コマ」の合成・構造と複屈折変化

結晶中でπ電子系が回転する「分子コマ」の合成・構造と複屈折変化