Diamagnetic Raman Optical Activity of Chlorine,Bromine, and Iodine Gases

Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties. Magnetic Raman optical activity has recently been observed in a paramagnetic gas (Angew. Chem. Int. Ed. 2012 , 51, 11058; Angew. Chem. 2012 , 124, 11220). In diamagnetic molecules, it has been considered too weak to be measurable. However, in chlorine, bromine and iodine vapors, we could detect a significant signal as well. Zeeman splitting of electronic ground‐state energy levels cannot rationalize the observed circular intensity difference (CID) values of about 10⁻⁴. These are explicable by participation of paramagnetic excited electronic states. Then a simple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is a general event observable under resonance conditions. The phenomenon sheds new light on the role of excited states in the Raman scattering, and may be used to probe molecular geometry and electronic structure.     

Modification of Enzyme Activity by Vibrational Strong Coupling of Water

Vibrational strong coupling (VSC) has recently emerged as a completely new tool for influencing chemical reactivity. It harnesses electromagnetic vacuum fluctuations through the creation of hybrid states of light and matter, called polaritonic states, in an optical cavity resonant to a molecular absorption band. Here, we investigate the effect of vibrational strong coupling of water on the enzymatic activity of pepsin, where a water molecule is directly involved in the enzyme's chemical mechanism. We observe an approximately 4.5‐fold decrease of the apparent second‐order rate constant k_cat/K_m when coupling the water stretching vibration, whereas no effect was detected for the strong coupling of the bending vibration. The possibility of modifying enzymatic activity by coupling water demonstrates the potential of VSC as a new tool to study biochemical reactivity.     

Organic Cocrystals: Beyond Electrical Conductivities and Field‐Effect Transistors (FETs)

Organic cocrystals based on noncovalent intermolecular interactions (weak interactions) have aroused interest owing to their unpredicted and versatile chemicophysical properties and their applications. In this Minireview, we highlight recent research on organic cocrystals on reducing the aggregation‐caused quenching (ACQ) effect, tuning light emission, ferroelectricity and multiferroics, optical waveguides, and stimuli‐responsiveness. We also summarize the progress made in this field including revealing the structure–property relationships and developing unusual properties. Moreover, we provide a discussion on current achievements, limitations and perspectives as well as some directions and inspiration for further investigation on organic cocrystals.     

Organoboron Complexes in Edge‐Sharing Macrocycles: The Triphyrin(2.1.1)–Tetraphyrin(1.1.1.1) Hybrid

The formation of a precisely designed environment predefined for stabilizing electron‐deficient atoms, such as boron(III), is an important approach for optimizing the properties of a chromophore. A triphyrin(2.1.1) motif built on the extended π‐system of a tetraphyrin(1.1.1.1) skeleton creates a new coordination environment, with a CNN set of donors confined in a limited space predefined for binding small cations. The entrapment of boron(III) in the triphyrin(2.1.1) sector, with formation of a direct B?C bond, significantly changes the optical response and the global aromatic character of the compound, leading to an extension of the π‐delocalisation.     

Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature‐Sensitive Polymers

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature‐sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble‐metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM‐capped Au NPs red‐shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red‐shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non‐monotonic or switchable on/off catalytic performance, respectively, of PNIPAM‐capped Au NPs.     

Near-IR Absorbing J-Aggregate of an Amphiphilic BF2-Azadipyrromethene Dye by Kinetic Cooperative Self-Assembly

A new amphiphilic BF₂-azadipyrromethene (aza-BODIPY) dye 1 has been synthesized using a Cu^I-catalyzed “click” reaction. For this dye, two self-assembly pathways that lead to different type of J-aggregates with distinct near-infrared optical properties have been discovered. The metastable off-pathway product displays a broad, structureless absorption band while the thermodynamically stable on-pathway aggregate exhibits the characteristic spectral features of a J-aggregate, that is, red-shifted intense absorption band with significantly narrowed linewidth. The morphology and structure of the aggregates were studied by atomic force microscopy, transmission and scanning electron microscopy. The aggregation processes of 1 were investigated by temperature- and concentration-dependent UV/Vis spectroscopy and evaluated by models for cooperative self-assembly.