Prediction of Fluorooxoborates with Colossal Second Harmonic Generation (SHG) Coefficients and Extremely Wide Band Gaps: Towards Modulating Properties by Tuning the BO3/BO3F Ratio in Layers

Fluorooxoborates have inspired investigations of deep‐ultraviolet (DUV) nonlinear optical (NLO) materials that can meet the multiple criteria. Herein, five stable structures with the composition of BaB₂O₃F₂ (I–V) are discovered using the ab initio evolutionary algorithm. Among them, BaB₂O₃F₂‐I has been synthesized experimentally and confirms the reliability of the method. All of the predicted structures possess extremely wide band gaps (8.1–9.0 eV). Moreover, four new structures exhibit giant second harmonic generation (SHG) coefficients (>3×KDP, d₃₆=0.39 pm V^?1). A novel type of the [BOF] layer with BO₃:BO₃F ratio of [1:1] is found in BaB₂O₃F₂‐II and BaB₂O₃F₂‐III. While BaB₂O₃F₂‐IV and BaB₂O₃F₂‐V are solely composed of the BO₃F group and have colossal SHG coefficients (ca. 4×KDP). It gives the direct evidence that the BO₃F group could generate strong SHG effect. Most importantly, the influences of BO₃:BO₃F ratio and their number density on band gap, birefringence and SHG effects are investigated.     

Surface‐Enhanced Raman Spectra Promoted by a Finger Press in an All‐Solid‐State Flexible Energy Conversion and Storage Film

Electrochemically up‐regulated surface‐enhanced Raman spectroscopy (E‐SERS) effectively increases Raman signal intensities. However, the instrumental requirements and the conventional measurement conditions in an electrolyte cell have hampered its application in fast and on‐site detection. To circumvent the inconveniences of E‐SERS, we propose a self‐energizing substrate that provides electrical potential by converting film deformation from a finger press into stored electrical energy. The substrate combines an energy conversion film and a SERS‐active Ag nanowire layer. A composite film prepared from a piezoelectric polymer matrix and surface‐engineered rGO that simultaneously presents high permittivity and low dielectric loss is the key component herein. Using our substrate, increased E‐SERS signals up to 10 times from a variety of molecules were obtained in the open air. Various tests on real‐life sample surfaces demonstrated the potentials of the substrate in fast on‐site detection.     

Asymmetric Synthesis of Chiral Cyclopentanes Bearing an All‐Carbon Quaternary Stereocenter by Zirconium‐Catalyzed Double Carboalumination

Herein, we report a zirconium‐catalyzed enantio‐ and diastereoselective inter/intramolecular double carboalumination of unactivated 2‐substituted 1,5‐dienes, which provides efficient and direct access to chiral cyclopentanes through the generation of two stereocenters, including one all‐carbon quaternary stereocenter, generally with excellent diastereo‐ and high enantioselectivity. This tandem carboalumination process creates two new C−C bonds as well as one C−Al bond, which can be oxidized in situ with O₂ or hydrolyzed. Furthermore, the obtained chiral cyclopentanes can be readily functionalized to provide various chiral compounds.     

Nickel‐Catalyzed Conjugate Addition of Silyl Ketene Imines to In Situ Generated Indol‐2‐ones: Highly Enantioselective Construction of Vicinal All‐Carbon Quaternary Stereocenters

The first enantioselective conjugate addition of silyl ketene imines to in situ generated indol‐2‐ones was performed in the presence of a chiral N ,N ′‐dioxide/Ni^II catalyst. This method provides efficient access to chiral β‐alkyl nitriles bearing congested vicinal all‐carbon quaternary stereocenters in up to 90 % yield with 23:1 d.r. and 98 % ee . The products enable facile transformations to chiral pyrroloindoline frameworks and spirocyclohexane oxindole derivatives. A possible transition state was also proposed to explain the origin of the asymmetric induction.     

A Single Stereodynamic Center Modulates the Rate of Self‐Assembly in a Biomolecular System

Chirality is a property of asymmetry important to both physical and abstract systems. Understanding how molecular systems respond to perturbations in their chiral building blocks can provide insight into diverse areas such as biomolecular self‐assembly, protein folding, drug design, materials, and catalysis. Despite the fundamental importance of stereochemical preorganization in nature and designed materials, the ramifications of replacing chiral centers with stereodynamic atomic mimics in the context of biomolecular systems is unknown. Herein, we demonstrate that replacement of a single amino acid stereocenter with a stereodynamic nitrogen atom has profound consequences on the self‐assembly of a biomolecular system. Our results provide insight into how the fundamental biopolymers of life would behave if their chiral centers were not configurationally stable, highlighting the vital importance of stereochemistry as a pre‐organizing element in biomolecular folding and assembly events.