Direct observation of long-range chirality transfer in a self-assembled supramolecular monolayer at interface in situ

Probing the adsorption configuration of methanol at a charged air/aqueous interface using nonlinear spectroscopy

Investigating the effects of electrolyte ions on the adsorption configuration of methanol at a charged interface is important for studying the interface structure of electrolyte solutions and the oxidation mechanism of methanol in fuel cells. This study uses sum frequency generation (SFG) and heterodyne-detected second harmonic generation (HD-SHG) to investigate the adsorption configuration of methanol at the air/aqueous interface of 0.1 M NaClO4 solution, 0.1 M HClO4 solution and pure water. The results elucidate that the ion effect in the electrolyte solution affects the interface's charged state and the methanol's adsorption conformation at the interface. The negatively charged surface of the 0.1 M NaClO4 solution and the positively charged surface of the 0.1 M HClO4 solution arise from the corresponding specific ionic effects of the electrolyte solution. The orientation angle of methyl with respect to the surface normal is 43.4° ± 0.1° at the 0.1 M NaClO4 solution surface and 21.5° ± 0.2° at the 0.1 M HClO4 solution surface. Examining these adsorption configurations in detail, we find that at the negatively charged surface the inclined orientation angle (43.4°) of methanol favors the hydroxymethyl production by breaking the C-H bond, while at the positively charged surface the upright orientation angle (21.5°) of methanol promotes the methoxy formation by breaking the O-H bond. These findings not only illuminate the intricate ion effects on small organic molecules but also contribute to a molecular-level comprehension of the oxidation mechanism of methanol at electrode interfaces.

Diagrammatic theory of magnetic and quadrupolar contributions to sum-frequency generation in composite systems

Second-order nonlinear processes like Sum-Frequency Generation (SFG) are essentially defined in the electric dipolar approximation. However, when dealing with the SFG responses of bulk, big nanoparticles, highly symmetric objects, or chiral species, magnetic and quadrupolar contributions play a significant role in the process too. We extend the diagrammatic theory for linear and nonlinear optics to include these terms for single objects as well as for multipartite systems in interaction. Magnetic and quadrupolar quantities are introduced in the formalism as incoming fields, interaction intermediates, and sources of optical nonlinearity. New response functions and complex nonlinear processes are defined, and their symmetry properties are analyzed. This leads to a focus on several kinds of applications involving nanoscale coupled objects, symmetric molecular systems, and chiral materials, both in line with the existing literature and opening new possibilities for original complex systems.

Photocontrolled Reversibly Chiral-Ordered Assembly Based on Cucurbituril

Chirality transfer and regulation, accompanied by morphology transformation, arouse widespread interest for application in materials and biological science. Here, a photocontrolled supramolecular chiral switch is fabricated from chiral diphenylalanine (l-Phe-l-Phe, FF) modified with naphthalene (2), achiral dithienylethene (DTE) photoswitch (1), and cucurbit[8]uril (CB[8]). Chirality transfer from the chiral FF moiety of 2 to a charge-transfer (CT) heterodimer consisting of achiral guest 1 and achiral naphthalene (NP) in 2 has been unprecedented achieved via the encapsulation of CB[8]. On the contrary, chirality transfer from chiral FF to NP cannot be conducted in only guest 2. Crucially, induced circular dichroism of the heterodimer can be further modulated by distinct light, attributing to reversible photoisomerization of the DTE. Meanwhile, topological nanostructures are changed from one-dimensional (1D) nanofibers to two-dimensional (2D) nanosheets in the orderly assembling process of the heterodimer, which further achieved reversible interconversion between 2D nanosheets and 1D nanorods with tunable-induced chirality stimulated by diverse light.