Give or Take: Effects of Electron-Accepting/-Withdrawing Groups in Red-Fluorescent BODIPY Molecular Rotors

Mapping microviscosity, temperature, and polarity in biosystems is an important capability that can aid in disease detection. This can be achieved using fluorescent sensors based on a green-emitting BODIPY group. However, red fluorescent sensors are desired for convenient imaging of biological samples. It is known that phenyl substituents in the β position of the BODIPY core can shift the fluorescence spectra to longer wavelengths. In this research, we report how electron-withdrawing (EWG) and -donating (EDG) groups can change the spectral and sensory properties of β-phenyl-substituted BODIPYs. We present a trifluoromethyl-substituted (EWG) conjugate with moderate temperature sensing properties and a methoxy-substituted (EDG) molecule that could be used as a lifetime-based polarity probe. In this study, we utilise experimental results of steady-state and time-resolved fluorescence, as well as quantum chemical calculations using density functional theory (DFT). We also explain how the energy barrier height (Ea) for non-radiative relaxation affects the probe’s sensitivity to temperature and viscosity and provide appropriate Ea ranges for the best possible sensitivity to viscosity and temperature.     

On a sub-supersolution method for the prescribed mean curvature problem

The paper is about a sub-supersolution method for the prescribed mean curvature problem. We formulate the problem as a variational inequality and propose appropriate concepts of sub-and supersolutions for such inequality. Existence and enclosure results for solutions and extremal solutions between sub-and supersolutions are established.     

Regio- and enantioselective intermolecular hydroacylation: substrate-directed addition of salicylaldehydes to homoallylic sulfides

We report a Rh-catalyzed, regio- and enantioselective intermolecular olefin hydroacylation under mild conditions. Hydroacylations between homoallylic sulfides, containing a substrate-bound directing group, and salicylaldehyde derivatives occur in the presence of a spiro-phosphoramidite ligand, (R)-SIPHOS-PE, to give α-branched ketones in >20:1 selectivity and up to 97% ee. Our conditions are also applicable to the asymmetric intermolecular hydroacylation of 1,2-disubstituted olefins.     

Domain identification for harmonic functions

The authors investigate the problem of identifying the domainG of a harmonic functionu such that Cauchy data are given on a known portion of the boundary ofG, while a zero Dirichlet condition is specified on the remaining portion of the boundary, which is to be found. Under certain conditions on the domainG, it is shown that the problem reduces to identifying the coefficients of an elliptic equation which, in turn, is converted into the problem of minimizing a functional. Under certain conditions onG, it is shown that the solution, if it exists, is unique. An application is pointed out for the problem of designing a vessel shape that realizes a given plasma shape.This work was completed with a financial support from the National Basic Research in the Natural Sciences.     

Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides

By exploring a new mode of nickel‐catalyzed cross‐coupling, a method to directly transform both aromatic and aliphatic aldehydes into either esters or amides has been developed. The success of this oxidative coupling depends on the appropriate choice of catalyst and organic oxidant, including the use of either α,α,α‐trifluoroacetophenone or excess aldehyde. Mechanistic data that supports a catalytic cycle involving oxidative addition into the aldehyde C? H bond is also presented.     

Rh-catalyzed desymmetrization of α-quaternary centers by isomerization-hydroacylation

We describe a Rh-catalyzed desymmetrization of all-carbon quaternary centers from α,α-bis(allyl)aldehydes by a cascade featuring isomerization and hydroacylation. This desymmetrization competes with two other novel olefin functionalizations that are triggered by C–H bond activation, including carboacylation and bisacylation. A BIPHEP ligand promotes enantioselective formation of α-vinylcyclopentanones. Mechanistic studies support irreversible and enantioselective olefin-isomerization followed by olefin-hydroacylation.     

GaAs photonic crystal cavity with ultrahigh Q: microwatt nonlinearity at 1.55 microm

We haves realized and measured a GaAs nanocavity in a slab photonic crystal based on the design by Kuramochi et al. [Appl. Phys. Lett. 88, 041112 (2006)]. We measure a quality factor Q=700,000, which proves that ultrahigh Q nanocavities are also feasible in GaAs. We show that owing to larger two-photon absorption in GaAs nonlinearities appear at the microwatt level and will be more functional in gallium arsenide than in silicon nanocavities.     

Enhancing the Viscosity-Sensitive Range of a BODIPY Molecular Rotor by Two Orders of Magnitude

Molecular rotors are a class of fluorophores that enable convenient imaging of viscosity inside microscopic samples such as lipid vesicles or live cells. Currently, rotor compounds containing a boron-dipyrromethene (BODIPY) group are among the most promising viscosity probes. In this work, it is reported that by adding heavy-electron-withdrawing −NO₂ groups, the viscosity-sensitive range of a BODIPY probe is drastically expanded from 5–1500 cP to 0.5–50 000 cP. The improved range makes it, to our knowledge, the first hydrophobic molecular rotor applicable not only at moderate viscosities but also for viscosity measurements in highly viscous samples. Furthermore, the photophysical mechanism of the BODIPY molecular rotors under study has been determined by performing quantum chemical calculations and transient absorption experiments. This mechanism demonstrates how BODIPY molecular rotors work in general, why the −NO₂ group causes such an improvement, and why BODIPY molecular rotors suffer from undesirable sensitivity to temperature. Overall, besides reporting a viscosity probe with remarkable properties, the results obtained expand the general understanding of molecular rotors and show a way to use the knowledge of their molecular action mechanism for augmenting their viscosity-sensing properties.     

Catalytic Alkyne Arylation Using Traceless Directing Groups

By using Pd⁰/Mandyphos, we achieved a three‐component aminoarylation of alkynes to generate enamines, which are then hydrolyzed to either α‐arylphenones or α,α‐diarylketones. This Pd‐catalyzed method overcomes established known pathways to enable the use of amines as traceless directing groups for C?C bond formation.