Yueshun Jiang

From Achiral Molecular Components to Chiral Supermolecules and Supercoil Self‐Assembly

The self-assembly in chloroform of a pair of achiral molecular compo- nents, 5-(4-dodecyloxybenzylidene)-(1H,3H)-2,4,6-pyrimidinetrione (1) and 4-ami- no-2,6-didodecylamino-1,3,5-triazine (2) was found to generate a mesoscopic super- coil structure some 10 mm in length and about 300 nm in diameter. The self-assembly process took over 1200 h to reach equilibrium in chloroform at room temperature. In this system of positive cooperativity, chiral supermolecules based on a network of hydrogen bonds are initially generated from 1 and 2. Further assembly of such chiral supermolecules results in the formation of the observed mesoscopic supercoil structure. Owing to the lack of chirality in 1 and 2, both left- and right-handed supercoils are observed.

X-ray photoelectron spectroscopy study of the synthesis of copper sulphide in Langmuir-Blodgett films

On the basis of work by Barraud et al. (A. Barraud et al., Mol. Cryst., Liq. Cryst., 134 (1986) 347), the process of H2S diffusion into Langmuir-Blodgett (LB) films of copper stearate and the formation of layers of copper sulphide with semiconducting properties were studied by X-ray photoelectron spectroscopy measurements. It was shown that the reaction rate is mainly controlled by the diffusion of H2S. Thus various non-stoichiometric products can be obtained by controlling the H2S pressure. At least two sulphur species were found in the product, the sulphur ion (S2-) and the sulphur molecular ion (S22-), and the S22-:S2- ratio seems to be related to the extent of reaction. Finally, the specific effect of the microenvironment of LB films and the characteristics of the reaction in the LB film are discussed.

Temperature-dependent FTIR study of a supramolecular mesophase from the self-assembly of melamine and barbituric acid derivatives

A supramolecular mesophase was prepared from molecular recognition directed self- assembly of two complementary molecular components, namely 5-(4-dodecyloxy- benzylidene)-2,4,6-(1H,3H)-pyrimidinetrione and 4-amino-2,6-didodecylamino-1,3,5triazine. Differential scanning calorimetry measurements indicate a mesophase having liquid crystalline properties. Infrared studies suggest that not only hydrogen bonds but also pi-aromatic stacking and van der Waals interactions direct the formation of the mesophase.

Formation of mesophase by hydrogen bond directed self-assembly between barbituric acid and melamine derivatives

Abstract The 1:1 mesophase was formed through molecular self-assembly directed by hydrogen bonding between light active barbituric acid derivative, 5-[4-dodecyloxybenzylidene]-2, 4, 6,-(1H, 3H)-pyrimidinetrione (B) and melamine derivative, 4-amino-2, 6-didodecylamino-1, 3, 5-triazine (M). It was found through temperature-dependent IR spectra that there are three kinds of hydrogen bonds with different strength in this mesophase. When dispersed in chloroform, this mesophase shows a double helical structure.

Aggregation behaviors of light-active barbituric acid molecular components in solution

Abstract Self-aggregation of light active barbituric acid derivatives and their self-assembly with melamine derivatives through hydrogen-bonding, π-aromatic stacking, and other weak interactions were studied by UV–visible absorption and fluorescence spectroscopy. PB12Me has the same fluorescence behavior as PB12 in chloroform though it cannot aggregate through a hydrogen-bond. AB12 and AB1 lead to different degrees of fluorescence splitting. When barbituric acid molecular components were self-assembled with melamine a similar splitting phenomenon was observed. It was shown that π-aromatic stacking resulted in the exclusive fluorescence changes and H-aggregates were formed in solution.

Frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group

The frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group were analyzed based on the electrochemical, UV-visible spectral and spectroelectrochernical results of five ferrocene derivatives, R-Fc-A1(P1), A1-Fc-A1(PII), D-Fc-R (PIII), D-Fc-A1(PIV) and D-Fc-A2(PV) (R, CH2OH; A1 CHO; A2, CH = C(CN)2 and D, ((318H37)2N-C6&-CH = CH). It was found that there are strong interactions of the LUMO (π a* ) of electron drawing substituents with 1e2g (dry, dr2 - y2) and e2u(ϕ4u, ϕ5u) of the ferrocenyl group because the energy levels of πA * and e2g, e2u of (Cp-)2 are close, which lower not only the energy levels of bonded orbits πA *+[ϕ4u] and dx 2\t-y2 of PI, PII, PIV and PV obviously, but also those of their non-bonded orbit,dxy For PIII, PIV and PV, there are strong interactions of HOMO (πD) of the electron pushing substituent with lelu (ϕ2u, ϕ3u) of the ferrocenyl group because the levels of πD and eluof (Cp-)2 are close, which result in the formation of anti-bonded orbit, πD\t-[ϕ3u], and bonded orbit, ϕ3u +[πD].

A novel amphiphilic push-pull ferrocene derivative: Langmuir–Blodgett films and second-order optical nonlinearity

Abstract The Langmuir–Blodgett (LB) films built from the mixture of an amphiphilic push–pull ferrocene derivative ( P ) and behenic acid were investigated. Langmuir films of P diluted by behenic acid exhibit a very good cohesion and the mixed films can easily be transferred onto solid substrates. Linear dichroism UV-visible and IR spectroscopy measurements of the mixed LB multilayers confirm that the molecules ( P ) are oriented to the substrate. The nonlinear optical experiments on the mixed monolayer deposited on the CaF 2 slide showed that P displayed efficient optical second harmonic generation (SHG) with a molecular hyperpolarizability ( β ) as high as 6.0×10 -29 e.s.u.

A novel amphiphilic ferrocene derivative containing a barbituric acid unit: synthesis and quadratic optical non-linearity

Abstract A novel amphiphilic ferrocene derivative ( P ) containing barbituric acid was designed and synthesized. It has a π-donor-switch-acceptor structure, in which the N , N -dioctadecylaniline unit serves as the electron donor, the ferrocene moiety as the switch, and the barbituric acid unit as the electron acceptor. The non-linear optical experiments show the lipid P displays efficient optical second harmonic generation (SHG) with a molecular hyperpolarizability (β) as high as 1.8 × 10 −28 e.s.u. The lipid P alone is unable to form a high quality monolayer at the gas-water interface. The molecular recognition of the lipid P and its complementary substrate-melamine derivative ( M ), at the gas-water interface, may significantly improve the monolayer formation of the lipid P . The improvement of the monolayer has been found to exhibit a temperature-dependent effect: at about 24.5 °C it reaches the optimum.

X-ray photoelectron spectroscopy of non-stoichiometric lead sulfide monolayers in stearic acid Langmuir-Blodgett films

Abstract The chemical state, composition and stability in air of monolayers of lead sulfide synthesized in stearic acid LB films at a H 2 S pressure of 1 Torr were studied mainly by X-ray photoelectron spectroscopy (XPS). Its S/Pb ratio is about 1.5:1. In air, the lead sulfide monolayer slowly decomposes to PbSt 2 , elemental sulfur and other sulfur compounds which escape in air in the form of H 2 S or SO 2 . After exposure to air for 77 days, the lead sulfide monolayer had decomposed about 90%, of which elemental sulfur is 62%.

Structural study on the alternating Langmuir—Blodgett films deposited with two complementary barbituric acid and melamine derivatives

Abstract Alternating Langmuir-Blodgett films were deposited with two complementary molecules: 5-(4- N,N -dioctadecyl aminobenzylidene)-2,4,6-(1H,3H)-pyrimidinetrione (B) and 4-amino-2,6-didodecylamino-1,3,5-triazine (M). Pressure-area isotherms were recorded. The transfer behavior of the alternating films was compared with that of the separate films of B. X-ray diffraction measurements confirm that the alternating films have a genuinely alternating structure: MBMB…MB. Transmission FTIR measurements reveal that in the separate films B is exclusively self-aggregated through the hydrogen bonding between the C=O and N−H on the barbituric ring of B, and in the alternating films new hydrogen bonds are formed between B and M at the expense of those of the initial self-aggregation. Polarized attenuated total reflectance Fourier transform infrared spectroscopy measurements show that in the alternating films the hydrocarbon chains stand almost vertically, in comparison with the separate films of B as well as of M. It is found that in the alternating films the 2-position carbonyl on the barbituric ring of B is perpendicular to the film plane. It is concluded that the interlayer hydrogen bonding between B and M gives rise to a better film structure.