Molecular aggregation by hydrogen bonding in cold-crystallization behavior of mixed nucleobases analyzed by temperature-controlled infrared spectroscopy.

The cold-crystallization behaviors of dodecyl-substituted nucleobases (adenine, uracil, and thymine) were analyzed. The dodecyl derivative from uracil alone did not exhibit cold crystallization; however, a mixture of adenine and uracil derivatives at a molar ratio of 1 : 1 exhibited cold crystallization. These results are similar to the thermal behavior of dodecyl derivatives of adenine and thymine alone and in mixtures reported in a previous study. Temperature-controlled infrared spectroscopy was used to observe the molecular assembly states of the liquid, supercooled state, and cold-crystallized compounds. Hydrogen-bonded molecular pairs in the high-temperature liquid state, multiple hydrogen-bonded networks in the supercooled state, and reverse Hoogsteen-type complementary hydrogen bonds in cold-crystallized compounds were observed using infrared spectroscopy. The heterogeneity of the system, due to multiple types of hydrogen bonding, retarded the crystallization rate, resulting in supercooling and cold crystallization. Infrared spectroscopy, which can be used to measure the aggregation state of molecules, including the liquid and supercooled states, is an effective analytical method for clarifying the process of cold crystallization.

Cold crystallization and photo-induced thermal behavior of alkyl-derivatized diarylethene molecules.

The thermal behavior of alkylated diarylethene molecules (2,3-bis(2,4,5-trimethyl-3-thienyl)-N-alkylmaleimides; DAE-Cn) was investigated. DAE-C1 and DAE-C2 exhibited cold crystallization, which is a heat-storage phenomenon. In addition, DAE-Cn showed photoisomerization; the open-ring isomer O-DAE-Cn was formed by visible light irradiation and transformed to the closed-ring isomer C-DAE-Cn by UV light irradiation. X-ray diffraction and optical microscopy analyses revealed that O-DAE-Cn exhibited cold crystallization and C-DAE-Cn showed poor crystallinity. UV irradiation (365 nm) inhibited cold crystallization, and visible light irradiation (525 nm) triggered cold crystallization, suggesting that heat storage by the cold crystallization of DAE-Cn can be photo-controlled.

Alkyl substituent-dependent systematic change in cold crystallization of azo molecules.

The thermal behavior of alkyl-derivatized 1-(2,4-dimethylphenylazo)-4-naphthol and 1-(2,4-dimethylphenylazo)-2-naphthol (2,4-DM-4-Cn and 2,4-DM-2-Cn, respectively) was investigated. The change in the position of the alkyl substituent led to a variation in the thermal behavior, including the cold crystallization, which is a heat-storing phenomenon. In addition, a comprehensive study of the alkyl chain length revealed that 2,4-DM-4-Cn had better crystallinity and exhibited cold crystallization with short alkyl chains. The π-π, C-H⋯N, and C-H⋯π interactions stabilized the crystal structure of 2,4-DM-4-Cn. On the other hand, the polymorphism of 2,4-DM-2-Cn inhibited the formation of a uniform crystalline phase during cooling, which led to poor crystallinity. The only difference between the compounds, the position of the substituent, resulted in a clear variation in the cold crystallization and heat storage properties.

Surface Structures Formed by a Copper(II) Complex of Alkyl-Derivatized Indigo.

Assembled structures of dyes have great influence on their coloring function. For example, metal ions added in the dyeing process are known to prevent fading of color. Thus, we have investigated the influence of an addition of copper(II) ion on the surface structure of alkyl-derivatized indigo. Scanning tunneling microscope (STM) analysis revealed that the copper(II) complexes of indigo formed orderly lamellar structures on a HOPG substrate. These lamellar structures of the complexes are found to be more stable than those of alkyl-derivatized indigos alone. Furthermore, 2D chirality was observed.

Five types of odd-even effect and crystal structure changes brought about by ω-phenylalkyl group in [Ni(dmit)2] complex salts.

A series of [Ni(dmit)2] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate) salts of ω-phenylalkyl-trimethylammonium (CnPh: n is the alkylene chain length; n = 2-5) have been prepared and characterized by X-ray crystallographic structural analysis. All complex salts are found to be composed of an alternating stack of [Ni(dmit)2] anions and CnPh cations, whereas the crystal structures are different in each complex. Interestingly, this series exhibited five types of odd-even effects in the crystal structures: 1. [Ni(dmit)2] anion length, 2. CnPh cation length, 3. orientation of the alkylene group against the terminal phenyl group, 4. relative orientation of the terminal phenyl group against [Ni(dmit)2] anions, 5. structure of dimerized [Ni(dmit)2] anions. The last odd-even effect led to an unusual vertical dimer structure. The vertical dimer is a unique structure in [M(dmit)2] complex salts (M = transition metal) and has not been reported. The introduction of a terminal phenyl group is concluded to have increased the steric effect and led to a marked structural difference between odd and even-numbered complex salts, i.e. the odd-even effect.

Thermally activated polymorphic transition from a 1D ribbon to a 2D carpet: squaric acid on Au(111).

Polymorphic transition from the 1D ribbon to the 2D carpet superstructure of squaric acid molecules on Au(111) was achieved through a thermally activated process. Our combined STM and DFT study revealed that the molecular arrangements in 1D and 2D superstructures are determined by the stability of their conformational isomers and assembled structures, respectively.

1,2-Bis(undecyl-sulfan-yl)benzene.

In the title compound, C(28)H(50)S(2), the alkyl chains adopt a fully extended all-trans conformation and each of them is almost perfectly planar. One of the alkyl chains is coplanar with the benzene ring and the other is twisted out of the benzene ring plane; the C-C-S-C torsion angles are 176.4 (2) and 80.8 (3)°. In the crystal structure, an inter-molecular S⋯S inter-action [3.2123 (13) Å] links the mol-ecules into a centrosymmetric dimer; dimers are linked through weak C-H⋯π and C-H⋯S inter-actions, forming a column along the a axis.

Formation and observation of dimers of a metal complex with long alkyl side chains aligned on a graphite surface.

Scanning tunnelling microscope was successfully applied to observe self-assembled molecular images of (bis(5-dodecylsalicylidene)ethylenediaminato)nickel(II) in the form of dimers on highly oriented pyrolytic graphite.