R. Lu

Self-assembly of a chiral lipid gelator controlled by solvent and speed of gelation.

Glutamine derivative 1 with two-photon absorbing units has been synthesized and was found to show gelation ability in some solvents. Its self-assembly in the gel phase could be controlled by the solvent and speed of gelation. For example, in DMSO the organogelator self-assembled into H-aggregates with weak exciton coupling between the aromatic moieties. On the other hand, in DMSO/diphenyl ether (1:9, v/v) the molecules formed 1D aggregates, but with strong exciton coupling due to the small distance between the chromophores. Moreover, the formation of these two kinds of aggregates could be adjusted by the ratio of DMSO to diphenyl ether. In DMSO/toluene, DMSO/butanol, DMSO/butyl acetate, and DMSO/acetic acid systems similar results were observed. Therefore, conversion of the packing model occurs irrespective of the nature of the solvent. Notably, a unique sign inversion in the CD spectra could be realized by controlling the speed of gelation in the DMSO/diphenyl ether (1:9, v/v) system. It was found that a low speed of gelation induces the gelator to adopt a packing model with strong pi-pi interactions between the aromatic units. Moreover, the gels, when excited at 800 nm, emit strong green fluorescence and the quantum chemical calculations suggest that intramolecular charge transfer leads to two-photon absorption of the gelator molecule.

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.

A Smart Gelator as a Chemosensor: Application to Integrated Logic Gates in Solution, Gel, and Film

A gelator that consisted of one benzimidazole moiety and four amide units was used as a chemosensor. We found that its absorption and emission spectra in solution were sensitive to two complementary chemical stimuli: protons and anions. Thus, YES and INH logic gates were obtained when absorbance was defined as an output. A combination gate of XNOR and AND with an emission output was also obtained. Moreover, wet gels in two solvents were used to construct two more-complicated three-input-three-output gates, owing to the existence of the gel phase as an additional output. Finally, in xerogel films that were formed from two kinds of wet gels, reversible changes in their emission spectra were observed when they were sequentially exposed to volatile acid and NH(3). Another combination two-output logic gate was obtained for xerogel films. Finally, three states of the gelator were used to construct not only basic logic gate, but also some combination gates because of their response to multiple chemical stimuli and their multiple output signals, in which one chemical input could erase the effect of another chemical input.

High‐Resolution Triple‐Color Patterns Based on the Liquid Behavior of Organic Molecules

Driven by anticipation of novel applications, enormous progress has been made in organic semiconductors since the 1950s. Historically, much of the initial work was centered on organic light-emitting diodes (OLEDs) [ 1 , 2 ] and photovoltaics (PVs) [ 3 , 4 ] due to their intensive applications. Owing to efforts from both academia and industry over the last two decades, the research interest has dramatically expanded to transistors, [ 5 ] sensors, [ 6 ] memories, [ 7 ] lasers, [ 8 ] etc. In organic microelectronics and optoelectronics, the ability to create scalable high-resolution patterns of semiconductor organic molecules still presents challenges for fabrication technology. As an example, a full-color microdisplay requires high-resolution red, green, and blue (RGB) OLEDs to be patterned in close proximity of micrometers. Current patterning techniques based on shadow-mask [ 9 ] and vapor-jet printing [ 10 ] suffer from low resolution, poor scalability, and complicated multistep processing. Previously, we demonstrated the template-directed growth technique as a promising method for patterning organic semiconductors with tunable physical properties. [ 11–13 ] Herein, we show the liquid behavior of appropriately selected dye molecules on prepatterned substrates. By further controlling the diffusion of molecules between designed patterns, we achieve heteropatterning of organic materials, that is, the thickness of organic molecule patterns differs in a controlled way over predefi ned areas. Further deposition of a second type of molecule on the heteropatterned structure produces high-resolution, ordered, triple-color organic patterns using only two dyes. In this study, we use N , N ′ -di[( N -(3,6-ditertbutylcarbazyl))n -decyl] quinacridone (DtCDQA), an orange light-emitting material with high quantum yield and multiple emission states in both liquid and solid solvents. [ 13 ]

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.

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.

Effect of interlayer molecular recognition on the structural and non-linear optical properties of alternating Langmuir-Blodgett films of two complementary molecular components

Abstract Alternating Langmuir-Blodgett films were successfully deposited with two complementary molecular components: 5-(4-N, N-dioctadecylaminobenzylidene)-2, 4, 6-(1H, 3H)-pyrimidinetrione (B) and 4-amino-2, 6-didodecylamino-1, 3, 5-triazine (M). It was found that the interlayer molecular recognition improved the deposition of B. Preliminary studies were made about the effect of interlayer molecular recognition on the second harmonic generation and UV-visible absorbance of the charge transfer band of B.

Porphyrin–TiO2 nanoparticle heterostructure assembly by Langmuir–Blodgett method

Abstract Surface pressure–area ( π –A) isotherm characteristics of 5,10,15-(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl) porphyrin monolayers on both the water and TiO 2 hydrosol subphases, the UV–vis absorption and fluorescence spectra of the monolayers deposited onto CaF 2 substrates are investigated. π –A isotherms find that the porphyrin ring extends to lie more flat on a TiO 2 hydrosol surface than on a water surface. The UV–vis absorption spectra of the deposited monolayers prove that the porphyrin TiO 2 nanoparticle heterostructure assembly is formed, in which the J-aggregated effect of porphyrin is weakened, comparing with that in the monolayer deposited from water subphase. The fluorescence spectra show that the fluorescent emission quenching by the photoinduced electron transfer from the excited porphyrin molecule to TiO 2 nanoparticle, occurs under excitation in the Soret band region of porphyrin.