Photochromic Dithienylethene‐Containing Triarylborane Derivatives: Facile Approach to Modulate Photochromic Properties with Multi‐addressable Functions

A series of dithienylethene‐containing triarylboranes has been designed, synthesized, and characterized. The electrochemistry, photophysics, and photochromic behavior have also been studied. The photophysical and photochromic properties could be facilely tuned in this system by varying the thiophene spacers (thiophene, thienothiophene, and bithiophene) between the dithienylethene and the dimesitylboron (BMes₂) or the position of the BMes₂ substitution in the thiophene spacers. The absorption of closed form has been found to be more sensitive towards the structural modification upon incorporation of the BMes₂ unit. Moreover, multi‐addressable photochromic reactivity is obtained upon addition of Lewis base (F^?), which is due to the formation of boron–Lewis base adduct. The dependence of the photophysical and photochromic properties on the thiophene spacers and the position of the BMes₂ substitution has been further supported by computational studies.     

Alkyltelluro Substitution Improves the Radical‐Trapping Capacity of Aromatic Amines

The synthesis of a variety of aromatic amines carrying an ortho‐alkyltelluro group is described. The new antioxidants quenched lipidperoxyl radicals much more efficiently than α‐tocopherol and were regenerable by aqueous‐phase N‐acetylcysteine in a two‐phase peroxidation system. The inhibition time for diaryl amine 9 b was four‐fold longer than recorded with α‐tocopherol. Thiol consumption in the aqueous phase was found to correlate inversely to the inhibition time and the availability of thiol is the limiting factor for the duration of antioxidant protection. The proposed mechanism for quenching of peroxyl radicals involves O‐atom transfer from peroxyl to Te followed by H‐atom transfer from amine to alkoxyl radical in a solvent cage.     

Total Synthesis of (±)- Cis -5-Hydroxycalamenene

A total synthesis of (±)-cis-5-hydroxycalamenene 1 has been achieved from tetralone 5, which in turn was prepared from 5-methoxy-α-tetralone 3. Grignard reaction of compound 5 with isopropylmagnesium chloride, followed by dehydration and aromatization, provided the substituted naphthalene 7 whose conversion to (±)-cis-5-hydroxycalamenene 1 was accomplished by demethylation, formylation, and hydrogenation.     

Differential dynamic microscopy of bacterial motility

We demonstrate a method for the fast, high-throughput characterization of the dynamics of active particles. Specifically, we measure the swimming speed distribution and motile cell fraction in Escherichia coli suspensions. By averaging over ～10(4) cells, our method is highly accurate compared to conventional tracking, yielding a routine tool for motility characterization. We find that the diffusivity of nonmotile cells is enhanced in proportion to the concentration of motile cells.     

New light on disordered ensembles: ab initio structure determination of one particle from scattering fluctuations of many copies

We report on the first experimental ab?initio reconstruction of an image of a single particle from fluctuations in the scattering from an ensemble of copies, randomly oriented about an axis. The method is applicable to identical particles frozen in space or time (as by snapshot diffraction from an x-ray free electron laser). These fluctuations enhance information obtainable from an experiment such as conventional small angle x-ray scattering.     

Crystallization mechanism of hard sphere glasses

In supercooled liquids, vitrification generally suppresses crystallization. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystallization of monodisperse hard-sphere glasses at constant volume (as in a colloid experiment). Multiple crystalline patches appear without particles having to diffuse more than one diameter. As these patches grow, the mobility in neighboring areas is enhanced, creating dynamic heterogeneity with positive feedback. The future crystallization pattern cannot be predicted from the coordinates alone: Crystallization proceeds by a sequence of stochastic micronucleation events, correlated in space by emergent dynamic heterogeneity.     

Optical manipulation of microparticles using whispering-gallery modes in a silicon nitride microdisk resonator

We demonstrate optical manipulation of 1?μm sized polystyrene microparticles on silicon nitride microdisk resonator devices using whispering-gallery modes in an integrated optofluidic chip. We demonstrate multiple trapping tracks and extended trapping ranges within single wavelengths through exciting high-order modes. We observe various sets of trapping tracks and ranges through exciting various resonance modes. We switch particle traveling tracks by tuning the laser wavelength to various wavelengths. We also observe microparticles assembling along the trapping tracks.     

Hamiltonian constructions of Kähler-Einstein metrics and Kähler metrics of constant scalar curvature

Assuming the existence of a real torus acting through holomorphic isometries on a Kähler manifold, we construct an ansatz for Kähler-Einstein metrics and an ansatz for Kähler metrics with constant scalar curvature. Using this Hamiltonian approach we solve the differential equations in special cases and find, in particular, a family of constant scalar curvature Kähler metrics describing a non-linear superposition of the Bergman metric, the Calabi metric and a higher dimensional generalization of the LeBrun Kähler metric. The superposition contains Kähler-Einstein metrics and all the geometries are complete on the open disk bundle of some line bundle over the complex projective spaceP _n. We also build such Kähler geometries on Kähler quotients of higher cohomogeneity.Partially supported by the NSF Under Grant No. DMS 8906809     

Schur product of matrices and numerical radius (range) preserving maps

Let F(A) be the numerical range or the numerical radius of a square matrix A. Denote by A ° B the Schur product of two matrices A and B. Characterizations are given for mappings on square matrices satisfying F(A ° B) = F(?(A) ° ?(B)) for all matrices A and B. Analogous results are obtained for mappings on Hermitian matrices.