A DNA-Stabilized Ag1812+ Cluster with Excitation-Intensity-Dependent Dual Emission

DNA-stabilized silver nanoclusters (DNA-AgNCs) are easily tunable emitters with intriguing photophysical properties. Here, a DNA-AgNC with dual emission in the red and near-infrared (NIR) regions is presented. Mass spectrometry data showed that two DNA strands stabilize 18 silver atoms with a nanocluster charge of 12+. Besides determining the composition and charge of DNA₂[Ag₁₈]¹²⁺, steady-state and time-resolved methods were applied to characterize the picosecond red fluorescence and the relatively intense microsecond-lived NIR luminescence. During this process, the luminescence-to-fluorescence ratio was found to be excitation-intensity-dependent. This peculiar feature is very rare for molecular emitters and allows the use of DNA₂[Ag₁₈]¹²⁺ as a nanoscale excitation intensity probe. For this purpose, calibration curves were constructed using three different approaches based either on steady-state or time-resolved emission measurements. The results showed that processes like thermally activated delayed fluorescence (TADF) or photon upconversion through triplet-triplet annihilation (TTA) could be excluded for DNA₂[Ag₁₈]¹²⁺. We, therefore, speculate that the ratiometric excitation intensity response could be the result of optically activated delayed fluorescence.     

Three-Photon Infrared Stimulation of Endogenous Neuroreceptors in Vivo

To interrogate neural circuits and crack their codes, in vivo brain activity imaging must be combined with spatiotemporally precise stimulation in three dimensions using genetic or pharmacological specificity. This challenge requires deep penetration and focusing as provided by infrared light and multiphoton excitation, and has promoted two-photon photopharmacology and optogenetics. However, three-photon brain stimulation in vivo remains to be demonstrated. We report the regulation of neuronal activity in zebrafish larvae by three-photon excitation of a photoswitchable muscarinic agonist at 50 pM, a billion-fold lower concentration than used for uncaging, and with mid-infrared light of 1560 nm, the longest reported photoswitch wavelength. Robust, physiologically relevant photoresponses allow modulating brain activity in wild-type animals with spatiotemporal and pharmacological precision. Computational calculations predict that azobenzene-based ligands have high three-photon absorption cross-section and can be used directly with pulsed infrared light. The expansion of three-photon pharmacology will deeply impact basic neurobiology and neuromodulation phototherapies.     

AM1, PM3, and PM5 calculations of the absorption maxima of basic organic dyes

The absorption maxima, λ_max, of various organic dyes such as indigo, azobenzene, phenylamine, hydrazone, anthraquinone, naphthoquinone, and malachite green were calculated using the AM1, PM3, and PM5 semiempirical molecular orbital theories with the configuration interaction singles (CIS) and random phase approximation (RPA) approaches. The calculated λ_max were then compared with the values obtained by CNDO/S, INDO/S, ab initio CIS, and time-dependent density functional theory (TD-DFT). We found that the λ_max values calculated by AM1, PM3, and PM5 were in good correlation with the observed λ_max values. When B3LYP/cc-pVDZ optimized geometries were used, the square of the correlation coefficients between the calculated and observed λ_max, , at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.891, 0.897, and 0.927, respectively. In particular, at PM5-RPA//B3LYP/cc-pVDZ was the largest among those obtained from all the other calculations including TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ . Accordingly, the standard deviation of the difference between observed and calculated λ_max by the linear regression function at PM5-RPA//B3LYP/cc-pVDZ was the smallest. It was therefore concluded that this method was the most promising for the prediction of λ_max of various dyes among the computational methods studied here. When AM1 optimized geometries were used, at the AM1-RPA, PM3-RPA, and PM5-RPA levels were 0.822, 0.841, and 0.901, respectively, and they were also comparable to that at TD/B3LYP/cc-pVDZ//B3LYP/cc-pVDZ. Therefore, although some calibration efforts may be needed for AM1 geometries, PM5-RPA(CIS)//AM1 may be a second candidate available for the prediction of the absorption maxima of dyes, especially in the case of emphasizing computational cost.     

Analysis of Excitations for a Groove Guide Resonator at 10 GHz by means of the FDTD Method

Various excitations of a new groove guide resonator working in the X-band (8 GHz – 12 GHz) are investigated by means of numerical simulations. For the numerical simulations the Finite-Difference Time-Domain method is used. The groove guide resonator, modelled both with and without excitation structures, is discretised in space. The results in the time domain are then transformed into the frequency domain in order to obtain the resonance frequency spectrum. Comparison between simulations with and without excitations shows the effect of the excitations on the resonance frequency spectrum. The results are compared with those of previous analytical methods.     

Anregungsraten und Zerfallsraten der ArII-4p 2 D 5 2/0 -4s2P 3/2 Niveaus und die leistungsgrenzen des 4880 Å-Lasers

Excitation and decay rates of the 4880 Å-ArII-laser transition pumped in a low-pressure arc yield a power limit for ArII high power lasers (arc diameter >1 cm), caused mainly by radiation trapping. Maximum power of the 4880 Å laser is Φ/L=70W/m±25%.     

侧链结构对PPV/C_(60)组合体系的激发传递和电荷转移过程的影响

本文考察不同的侧链长度对聚对苯乙炔 (PPV)衍生物的光学性质等的影响 ,以及PPV/C60 的组合薄膜中的激发传递和电荷转移过程。结果表明随着连接在PPV的侧链长度的增长 ,其π π 跃迁带隙变窄 ,使得吸收和发射峰的位置逐渐红移 ;同时观测到PPV/C60 间存在着极有效的激发传递过程 ,从而使得PPV衍生物的荧光在很大程度上被C60 分子所猝灭 ;MD PPV/C60 组合膜中观测到了C-60 的吸收峰 ,这表明该体系存在着基态电荷转移过程 ,同时也表明PPV衍生物与C60 分子间的相互作用和PPV的侧链长短密切相关。     

Excitation energies, electron affinities and ionization potentials of the transition metals V, Cr and Mn

 Configuration interaction calculations were carried out for neutral ground and excited states and positively and negatively ionized states of the V, Cr and Mn atoms. Energy convergence with respect to systematic expansion of both the one-electron and configuration bases was investigated for valence correlation. Contributions from core electrons to the differential correlation energies and relativistic effects were evaluated separately. Assuming additivity of these contributions, excitation energies, electron affinities and ionization potentials of the atoms were obtained. All calculated values were in excellent agreement with the observed values within a deviation of 0.056 eV except for the electron affinity of the V atom, which had a calculated value 0.110 eV larger than the experimental value. Received: 9 August 2000 / Accepted: 26 October 2000 / Published online: 3 April 2001     

Parametric study of an atmospheric pressure microwave-induced plasma of the mini MIP torch — II. Two-dimensional spatially resolved excitation temperature measurements

Two-dimensional mapping of the excitation temperatures have been carried out in the microwave-induced plasma torch with tangential argon flow. It is detected that the presence of wet aerosols in a nebulizer gas increases axial excitation temperature while desolvation acts in the opposite direction. The influence of low hydrogen concentration in the support gas and potassium in the nebulizer gas on the temperature distribution is studied in detail. The comparison of excitation temperature and electron number density distributions clearly indicates non-equilibrium plasma conditions.     

Imaging fingerprinting of excitation emission matrices

The spectral fingerprinting of the excitation emission matrix (EEM) of fluorescent substances is demonstrated using polychromatic light sources and tri-chromatic image detectors. A model of the measured fingerprints explaining their features and classification performance, based on the polychromatic excitation of the indicators is proposed.Substantial amount of spectral information is retained in the fingerprints as corroborated by multivariate analysis and experimental conditions that favor such situation are identified.In average, for five different substances, the model shows a fitting goodness measured by the Pearson's r coefficient and the root mean square deviation of 0.8541 and 0.0247 respectively, while principal component classification patterns satisfactorily compare with the EEM spectroscopy classification and respectively explain 96% and 93% of the information in the fist two principal components.The measurements can be performed using regular computer screens as illumination and web cameras as detectors, which constitute ubiquitous and affordable platforms compatible with distributed evaluations, in contrast to regular instrumentation for EEM measurements.     

Synchronous fluorescence and excitation emission characteristics of transformer oil ageing

This paper describes the evaluation of synchronous fluorescence spectroscopy (SFS) and excitation emission matrix fluorescence (EEMF) spectroscopy as means of monitoring transformer oil degradation. When accelerated thermal ageing method is used, the onset of degradation of transformer oil on 17th day and transformer oil with polypropylene and cellulosic paper on 23rd and 27th days is sensitively reflected in the SFS and EEMF fluorescence spectral characteristics.