New luminescent “carbene–metal–amide” (CMA) Cu, Ag, and Au complexes based on monocyclic (C6) or bicyclic six-ring (BIC6) cyclic (alkyl)(amino)carbene ligands illustrate the effects of LUMO energy ...stabilization, conformational flexibility, excited state energy, and geometry on the photoluminescent properties, leading to 100% luminescence quantum yields, short excited state lifetimes Cu > Au > Ag down to 0.5 μs, and high radiative rates of 106 s–1. Gold complexes with the BIC6 ligand exhibit exceptional photostability under hard and soft UV light compared with analogous complexes with C5 and C6 carbenes. Steady-state and time-resolved photoluminescence spectroscopy at 298 and 77 K enabled an estimate of the energy levels of the charge transfer (CT) and locally excited (LE) states with singlet and triplet character. A four-state model is applied to describe thermally activated delayed fluorescence (TADF) properties in CMA materials and correlates excited state lifetimes with the energy difference between LE and CT states.
The mathematical assessment of effect of uncertainty components on measurement results in using concentration ratio calibration in inductively coupled plasma atomic emission spectrometry was ...performed. Formulas for the calculation of the relative standard uncertainty for different components were derived. It was shown that, in different scenarios of using concentration ratio calibration, the combined standard uncertainty basically depends on the repeatability of the determination of the intensity ratio of the analytical line of a test element to the line of the main matrix component of the sample.
The results obtained by calculating the rate of muon transfer from the
state of muonic protium to a free-oxygen nucleus in the collision-energy range between
and 10 eV are presented. The calculation ...was based on the method of perturbed stationary states used within a version proposed earlier. Electron screening in the entrance channel of the transfer reaction was taken into account. The existence of a
-wave resonance in the reaction rate at a collision energy of about 0.1 eV is predicted. This result is of interest in the context of the planned laser experiment aimed at a precision measurement of the energy of hyperfine splitting of the
state of muonic protium.
Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable ...solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.
Conformationally flexible "Carbene-Metal-Amide" (CMA) complexes of copper and gold have been developed based on a combination of sterically hindered cyclic (alkyl)(amino)carbene (CAAC) and 6- and ...7-ring heterocyclic amide ligands. These complexes show photoemissions across the visible spectrum with PL quantum yields of up to 89% in solution and 83% in host-guest films. Single crystal X-ray diffraction and photoluminescence (PL) studies combined with DFT calculations indicate the important role of ring structure and conformational flexibility of the amide ligands. Time-resolved PL shows efficient delayed emission with sub-microsecond to microsecond excited state lifetimes at room temperature, with radiative rates exceeding 10
6
s
−1
. Yellow organic light-emitting diodes (OLEDs) based on a 7-ring gold amide were fabricated by thermal vapor deposition, while the sky-blue to warm-white mechanochromic behavior of the gold phenothiazine-5,5-dioxide complex enabled fabrication of the first CMA-based white light-emitting OLED.
Conformationally flexible "Carbene-Metal-Amide" (CMA) complexes of copper and gold show photoemissions across the visible spectrum, including mechanochromic behavior which led to the first CMA-based white light-emitting OLED.
Carbene-metal-amides are soluble and thermally stable materials which have recently emerged as emitters in high-performance organic light-emitting diodes. Here we synthesise carbene-metal-amide ...photoemitters with CF
-substituted ligands to show sky-blue to deep-blue photoluminescence from charge-transfer excited states. We demonstrate that the emission colour can be adjusted from blue to yellow and observe that the relative energies of charge transfer and locally excited triplet states influence the performance of the deep-blue emission. High thermal stability and insensitivity to aggregation-induced luminescence quenching allow us to fabricate organic light-emitting diodes in both host-free and host-guest architectures. We report blue devices with a peak external quantum efficiency of 17.3% in a host-free emitting layer and 20.9% in a polar host. Our findings inform the molecular design of the next generation of stable blue carbene-metal-amide emitters.
Gold-centered carbene-metal-amides (CMAs) containing cyclic (alkyl)(amino)carbenes (CAACs) are promising emitters for thermally activated delayed fluorescence (TADF). Aiming at the design and ...optimization of new TADF emitters, we report a density functional theory study of over 60 CMAs with various CAAC ligands, systematically evaluating computed parameters in relation to photoluminescence properties. The CMA structures were primarily selected based on experimental synthesis prospects. We demonstrate that TADF efficiency of the CMA materials originates from a compromise between oscillator strength coefficients and exchange energy (ΔE
). The latter is governed by the overlap of HOMO and LUMO orbitals, where HOMO is localized on the amide and LUMO over the Au-carbene bond. The S
ground and excited T
states of the CMAs adopt approximately coplanar geometry of carbene and amide ligands, but rotate perpendicular in the excited S
states, resulting in degeneracy or near-degeneracy of S
and T
, accompanied by a decrease in the S
-S
oscillator strength from its maximum at coplanar geometries to near zero at rotated geometries. Based on the computations, promising new TADF emitters are proposed and synthesized. Bright CMA complex (
CAAC)Au(carbazolide) is obtained and fully characterized in order to demonstrate that excellent stability and high radiative rates up to 10
s
can be obtained for the gold-CMA complexes with small CAAC-carbene ligands.
The effect of the heavy metal atom on the photophysics of carbene‐metal‐amide (CMA) photoemitters is explored, where the metal bridge is either Au, Ag, or Cu. Spectroscopic investigations reveal the ...coupling mechanism responsible for communication between the singlet and triplet manifolds. The photophysical properties do not reflect expected trends based upon the heavy atom effect, as both direct coupling between charge‐transfer states and spin‐vibronic coupling via a ligand‐centered triplet state are present. Direct coupling is weakest for CMA(Ag), increasing the importance of the spin‐vibronic pathway and rendering its properties more sensitive to inter‐state energy gaps than for the Au and Cu‐bridged analogues. The measured activation energy correlates with the expected exchange energy of the charge‐transfer state, which is also closely related to the length of the bonds joining the carbene and amide ligands, and decreases in the order CMA(Cu) > CMA(Au) > CMA(Ag). These findings reveal that reducing interference between charge‐transfer and ligand‐centers excited, and minimizing exchange energy, are required for developing efficient luminescent CMA complexes.
The influence of the metal atom on the photophysics of carbene‐metal‐amide (CMA) photoemitters is explored. Measured intersystem crossing (ISC) rates are ordered CMA(Cu) > CMA(Au) > CMA(Ag). Reverse ISC depends strongly on activation energy, with rates ordered CMA(Ag) > CMA(Au) > CMA(Cu). Coupling between the singlet and triplet manifolds is not therefore governed by the heavy atom effect.
The International Commission on Radiological Protection (ICRP) has embarked on a review and revision of the system of Radiological Protection that will update the 2007 general recommendations in ICRP
.... This is the beginning of a process that will take several years, involving open and transparent engagement with organisations and individuals around the world. While the system is robust and has performed well, it must adapt to address changes in science and society to remain fit for purpose. The aim of this paper is to encourage discussions on which areas of the system might gain the greatest benefit from review, and to initiate collaborative efforts. Increased clarity and consistency are high priorities. The better the system is understood, the more effectively it can be applied, resulting in improved protection and increased harmonisation. Many areas are identified for potential review including: classification of effects, with particular focus on tissue reactions; reformulation of detriment, potentially including non-cancer diseases; re-evaluation of the relationship between detriment and effective dose, and the possibility of defining detriments for males and females of different ages; individual variation in the response to radiation exposure; heritable effects; and effects and risks in non-human biota and ecosystems. Some of the basic concepts are also being considered, including the framework for bringing together protection of people and the environment, incremental improvements to the fundamental principles of justification and optimisation, a broader approach to protection of individuals, and clarification of the exposure situations introduced in 2007. In addition, ICRP is considering identifying where explicit incorporation of the ethical basis of the system would be beneficial, how to better reflect the importance of communications and stakeholder involvement, and further advice on education and training. ICRP invites responses on these and other areas relating to the review of the System of Radiological Protection.
This paper is concerned with investigating the capabilities of wave tomography methods via supercomputer numerical simulations on a model problem of imaging the wave velocity structure inside flat ...solid objects. The problem of reconstructing the velocity structure is formulated as a nonlinear coefficient inverse problem. Iterative algorithms for solving this inverse problem are based on computing the gradient of the residual functional between the experimentally measured wave field and the numerically computed wave field. A tomographic diagnostic method is proposed for imaging flat objects which are accessible only from a single side. The method employs two ultrasonic transducer arrays and takes into account reflections from the flat bottom of the object, assuming that the thickness of the object is known. The use of the reflections from the bottom is a key feature of the method, since it significantly increases the number of sounding angles and allows the transmitted waves to be registered. This study compares the results of solving inverse problems with complete and incomplete data sets. The proposed scalable numerical algorithms can be efficiently parallelized on supercomputers. The computations were performed on 50 CPU cores of the ‘‘Lomonosov-2’’ supercomputer at Lomonosov Moscow State University. Numerical simulations were carried out for various tomographic schemes using the high-performance algorithms and supercomputer software developed in this study. The acoustic and geometric parameters of the simulations correspond to a real experiment on nondestructive testing (NDT) of solids.
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