Electron Energies, Dipole Electric Moments, and Distribution of the Laurdan Molecule over the Conformation States of Methyl Groups

Using the methods of molecular simulation and HyperChem v.5.0 programs (PM3 method), we carried out calculations of the principal spectroscopic characteristics and of the structure of the laurdan molecule in the ground and the first excited electronic states. The thermal static distribution of molecules over various possible orientations LE" BORDER="0"> of the plane of methyl groups relative to the plane of the naphthalene bicycle was taken into account. The energies and dipole moments of these electronic states have been calculated as functions of the torsion angle of methyl groups. The existence of an additional mechanism of electronic spectrum broadening is shown; it is associated with thermal mismatch of the equilibrium orientations of the rotational fragment of the molecule and with the dependence of the electron transition frequency on the degree of deviation of the angle LE" BORDER="0"> from the equilibrium value. The dependence of dipole moments on this angle has been found and calculated. This dependence is the strongest for the ground state. The maximum values of dipole moments in the ground and excited states are 4.0 and 7.6 D.     

Luminescence of Molecules with Internal Charge Transfer upon Longwave Excitation

We have studied the spectral properties of luminescence of laurdan molecules in glycerin upon excitation at the red edge of the absorption band at different temperatures. The most significant red-wave shift of the spectra (LE" BORDER="0">10 nm) for the longwave band of dual fluorescence is observed depending on the excitation wavelength at a low temperature of 260 K when a solvent forms a fairly rigid matrix. At the same time, at increased temperatures of up to 370 K a small bathochromic shift and a change in the shape of the luminescence bands are also recorded reliably. Changes in the excitation spectra were observed when luminescence was recorded in the bands of the LE- and CT states. The difference spectrum responsible for the additional absorption that does not make a contribution to the longwave luminescence component has been isolated. The decay kinetics of both luminescence components have been measured and their expansions in decay constants have been analyzed. The experimental dependences obtained point to the complex mechanism of inhomogeneous broadening of spectra.     

Time‐dependent density functional theory study on the hydrogen bonding‐induced twisted intramolecular charge‐transfer excited states of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine

In this work, the time‐dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen‐bonded intramolecular charge‐transfer excited state of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine (DMAPIP) in methanol (MeOH) solvent. All the geometric conformations of the ground state and locally excited (LE) state and the twisted intramolecular charge‐transfer (TICT) state for isolated DMAPIP and its hydrogen‐bonded complexes have been optimized. At the same time, the absorption and fluorescence spectra of DMAPIP and the hydrogen‐bonded complexes in different electronic states are also calculated. We theoretically demonstrated for the first time that the intermolecular hydrogen bond formed between DMAPIP and MeOH can induce the formation of the TICT state for DMAPIP in MeOH solvent. Therefore, the two components at 414 and 506 nm observed in the fluorescence spectra of DMAPIP in MeOH solvent were reassigned in this work. The fluorescence peak at 414 nm is confirmed to be the LE state. Furthermore, the red‐shifted shoulder at 506 nm should be originated from the hydrogen‐bonded TICT excited state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Thermal analysis and expected performance of the low energy instrument on board the HXMT satellite

The Low Energy X-ray Instrument (LE) of the Hard X-ray Modulation Telescope (HXMT) uses the Swept Charge Device (SCD) to detect the X-rays in 1-15 keV. The performance of SCD is vulnerable to temperature. We analyzed the thermal condition of LE at different satellite working attitudes with the Finite Element Method (FEM). It is shown that the angle between the sunlight and the normal line of the barrier should be less them 26°, to keep the SCD detectors working in the required temperature range, i.e. -40 ℃ to -80 ℃. We find that the performance of LE is very stable in this temperature range, with a typical energy resolution of 160 eV at 5.9 keV.     

Interpreting divergences and Madelung-type sums via extrapolations of sequence generating polynomials: Method of intersection and area rule

Based on explorations in estimating certain Madelung constants, we put forward here two separate strategies to understand the meaning of two distinct classes of divergent non-power-series expansions. One class refers to alternating series representations, the other to monotonic ones. They chiefly rest on precise and approximate polynomial extrapolations, depending on situations. In case of sawtooth sequences, e.g., the partial-sums obtainable from Dirichlet eta or beta function at negative integer arguments, exact sequence-generating polynomials are found. Extrapolations yield a graphical meaning to anti-limit here, along with the exact answer. For staircase sequences, like the ones obtained from partial-sums of series representations for lambda and zeta functions, again at negative integer arguments, anti-limits do not exist. But, correct sequence-generating polynomials are obtained. There, our recipe relies on estimation of specific, finite areas embedded by such polynomials. The schemes put forward here are direct, independent and conceptually appealing. A subsequent extension of the latter strategy to alternating series also lends extra credence. Two new interpretations of summability are gained. Pilot calculations on several types of lattice sums reveal the worth of our endeavor with approximate extrapolations as well.     

Turing Patterns in a Reaction-Diffusion System

We have further investigated Turing patterns in a reaction-diffusion system by theoretical analysis and numerical simulations. Simple Turing patterns and complex superlattice structures are observed. We find that the shape and type of Turing patterns depend on dynamical parameters and external periodic forcing, and is independent of effective diffusivity rate σ in the Lengyel-Epstein model. Our numerical results provide additional insight into understanding the mechanism of development of Turing patterns and predicting new pattern formations.     

Anomalous Inhomogeneous Broadening of the Electronic Spectra of N,N-Dimethylaminobenzonitrile in Solutions

The anomalously large spectral inhomogeneity of the electronic bands ( LE" BORDER="0"> 145 nm) of N,N-dimethylaminobenzonitrile in a polar solution of glycerin demonstrating intramolecular charge transfer in an excited state has been revealed and investigated. In a nonpolar solution of n-hexane there is no substantial manifestation of inhomogeneous broadening. The results obtained are explained by the influence exerted by the luminophor-molecule microsurrounding in a polar solution on the broadening of spectra and by the characteristic features associated with mobile groupings of atoms in the molecule.     

Measurements of charge transfer ef f iciency in a proton-irradiated swept charge device

Charged Coupled Devices(CCDs) have been successfully used in several low energy X-ray astronomical satellites over the past two decades. Their high energy resolution and high spatial resolution make them a perfect tool for low energy astronomy, such as observing the formation of galaxy clusters and the environment around black holes. The Low Energy X-ray Telescope(LE) group is developing a Swept Charge Device(SCD) for the Hard Xray Modulation Telescope(HXMT) satellite. A SCD is a special low energy X-ray CCD, which can be read out a thousand times faster than traditional CCDs, simultaneously keeping excellent energy resolution. A test method for measuring the charge transfer efficiency(CTE) of a prototype SCD has been set up. Studies of the charge transfer inefficiency(CTI) with a proton-irradiated SCD have been performed at a range of operating temperatures. The SCD is irradiated by 3×108cm-210 MeV protons.     

白光LED的最新进展

重点对近年来白光LED的进展进行评述,同时介绍一些在这方面的研究结果。     

Optimized synthesis of new LE404-derived azecine-prodrugs

Dibenzoazecines represent a class of high-affinity dopamine and serotonin receptor antagonists. The former synthesis of the lead structure 7-methyl-5,6,7,8,9,14-hexahydrodibenzo[d,g]azecin-3-ol (LE404) has been 5 steps with a total yield of 13%. The present work enabled the synthesis of LE404 with a much higher yield. Based on this research, further azecin derivatives were synthesized with the aim to improve pharmacokinetic parameters.