Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation‐induced emission (AIE) materials and applications. We first note that the intermolecular ...excitonic coupling is much weaker in strength than the intramolecular electron‐vibration coupling for a majority of newly termed AIEgens, which leads to the emission peak position insensitive to excitonic coupling, hence the conventional excitonic model for J‐aggregation cannot effectively explain their AIE phenomena. Then, using multiscale computational approach coupled with our self‐developed thermal vibration correlation function rate formalism and transition‐state theory, we quantitatively investigate the aggregation effect on both the radiative and the nonradiative decays of molecular excited states. For radiative decay processes, we propose that the lowest excited state could convert from a transition dipole‐forbidden “dark” state to a dipole‐allowed “bright” state upon aggregation. For the radiationless processes, we demonstrate the blockage of nonradiative decay via vibration relaxation (BNR‐VR) in harmonic region or the removal of nonradiative decay via isomerization (RNR‐ISO) or minimum energy crossing point (RNR‐MECP) beyond harmonic region in a variety of AIE aggregates. Our theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally verified. Looking forward, we believe this review will benefit the deep understanding about the universality of AIE phenomenon and further extending the scope of AIE systems with novel applications.
This review provides a comprehensive and profound theoretical picture of the inherent luminescence mechanism of AIE in a variety of AIEgens, which will be helpful to deeply understanding the universality of AIE phenomenon and further extending the scope of AIE systems and exploiting new applications.
Room-temperature phosphorescence (RTP) with long afterglow from pure organic materials has attracted great attention for its potential applications in biological imaging, digital encryption, ...optoelectronic devices, and so on. Organic materials have been long considered to be nonphosphorescent owing to their weak molecular spin–orbit coupling and high sensitivity to temperature. However, recently, some purely organic compounds have demonstrated highly efficient RTP with long afterglow upon aggregation, while others fail. Namely, it remains a challenge to expound on the underlying mechanisms. In this study, we present the molecular descriptors to characterize the phosphorescence efficiency and lifetime. For a prototypical RTP system consisting of a carbonyl group and π-conjugated segments, the excited states can be regarded as an admixture of n → π* (with portion α) and π → π* (portion β). Starting from the phosphorescent process and El-Sayed rule, we deduced that (i) the intersystem crossing (ISC) rate of S1 → T n is mostly governed by the modification of the product of α and β and (ii) the ISC rate of T1 → S0 is determined by the β value of T1. Thus, the descriptors (γ = α × β, β) can be employed to describe the RTP character of organic molecules. From hybrid quantum mechanics and molecular mechanics (QM/MM) calculations, we illustrated the relationships among the descriptors (γ, β), phosphorescence efficiency and lifetime, and spin–orbit coupling constants. We stressed that the large γ and β values are favorable for the strong and long-lived RTP in organic materials. Experiments have reported confirmations of these molecular design rules.
An effective condition monitoring system of wind turbines generally requires installation of a high number of sensors and use of a high sampling frequency in particular for monitoring of the ...electrical components within a turbine, resulting in a large amount of data. This can become a burden for condition monitoring and fault detection systems. This paper aims to develop algorithms that will allow a reduced dataset to be used in wind turbine fault detection. This paper first proposes a variable selection algorithm based on principal component analysis with multiple selection criteria in order to select a set of variables to target fault signals while still preserving the variation of data in the original dataset. With the selected variables, this paper then describes fault detection and identification algorithms, which can identify faults, determine the corresponding time and location where the fault occurs, and estimate its severity. The proposed algorithms are evaluated with simulation data from PSCAD/EMTDC, Supervisory control and data acquisition data from an operational wind farm, and experimental data from a wind turbine test rig. Results show that the proposed methods can select a reduced set of variables with minimal information lost whilst detecting faults efficiently and effectively.
Electrically pumped organic lasing is one of the most challenging issues in organic optoelectronics. We present a systematic theoretical investigation to screen out electrical pumping lasing ...molecules over a wide range of organic materials. With the electronic structure information obtained from time-dependent density functional theory, we calculate multiple photophysical parameters of a set of optical pumping organic laser molecules in our self-developed molecular material property prediction package (MOMAP) to judge whether the electrically pumped lasing conditions can be satisfied, namely, to avoid reabsorption from excitons and/or polarons, and the accumulation of triplet excitons. In addition, a large oscillator strength of S1 and weak intermolecular π–π interaction are preferred. With these criteria, we are able to conclude that BP3T, BSBCz, and CzPVSBF compounds are promising candidates for electrically pumped lasing, and the proposed computational strategy could serve as a general protocol for molecular design of organic lasing materials.Though the goal of current organic solid-state laser research remains the realization of electrically pumped lasing, identifying organic semiconductors with ideal properties remains a challenge. Here, the authors report a computational strategy for screening electrical pumping lasing molecules.
Theoretical understanding of organic light-emitting diodes started from the quest to the nature of the primary excitation in organic molecular and polymeric materials. We found the electron ...correlation strength, bond-length alternation as well as the conjugation extent have strong influences on the orderings of the lowest lying excited states through the first application of density matrix renormalization group theory to quantum chemistry. The electro-injected free carriers（with spin 1/2） can form both singlet and triplet bound states. We found that the singlet exciton formation ratio can exceed the conventional 25% spin statistics limit. We proposed a vibration correlation function formalism to evaluate the excited-state decay rates, which is shown to not only give reasonable estimations for the quantum efficiency but also a quantitative account for the aggregation-induced emission（AIE）. It is suggested to unravel the AIE mechanism through resonance Raman spectroscopy.
This paper presents data-driven approaches to improve the active power output of wind turbines based on estimating their health condition. The main procedure includes estimations of fault degree and ...health condition level, and optimal power dispatch control. The proposed method can adjust the active power output of individual turbines according to their health condition and can thus optimize the total energy output of a wind farm. In the paper, extreme learning machine algorithm and Bonferroni interval are applied to estimate fault degree, while an analytic hierarchy process is used to estimate the health condition level. A scheme for power dispatch control is formulated based on the estimated health condition. Models have been identified from supervisory control and data acquisition data acquired from an operational wind farm, which contains temperature data of gearbox bearing and generator winding. The results show that the proposed method can maximize the operation efficiency of the wind farm while significantly reducing the fatigue loading on the faulty wind turbines.
The new round of Healthcare Reform in China has implemented over 3 years since 2009, and promoted greatly the development of public county hospitals. The purpose of this study is to evaluate county ...hospitals efficiency before and after the healthcare reform, and further assess the reform effectiveness through the comparative analysis of the efficiency.
Data envelopment analysis (DEA) was employed to calculate the efficiency of 1105 sample hospitals which were selected from 31 provinces of China, also, Tobit regression was used to regress against those main external environmental factors.
Our results show that the scales and amounts of service of hospitals had increased sharply, however, the efficiency was relatively low and decreased slightly from 2008 to 2012. Thirteen (1.18%) in 2008 and six (0.54%) hospitals in 2012 were defined as technically efficient, and the average scores were 0.2916 and 0.2503. The technical efficiency average score of the post-reform was significantly less than that of the pre-reform (p < 0.001), and the score of eastern region was highest and the western was lowest among three regions of China.
It suggests the reform had not well improved county hospital efficiency although hospitals have reached a fair developing scale, and the corresponding policies and measures should be put into effect for improving efficiency, especially in the level and structure of health investment, operation and supervision mechanism of county hospitals.
Long‐lived phosphorescence at room temperature (RTP) from pure organic molecules is rare. Recent research reveals various crystalline organic molecules can realize RTP with lifetimes extending to the ...magnitude of second. There is little research on how molecular packing affecting RTP. Three compounds are designed with similar optical properties in solution, but tremendously different solid emission characteristics. By investigating the molecular packing arrangement in single crystals, it is found that the packing style of the compact face to face favors of long phosphorescence lifetime and high photoluminescence efficiency, with the lifetime up to 748 ms observed in the crystal of CPM ((9H‐carbazol‐9‐yl)(phenyl)methanone). Theoretical calculation analysis also reveals this kind of packing style can remarkably reduce the singlet excited energy level and prompt electron communication between dimers. Surprisingly, CPM has two very similar single crystals, labeled as CPM and CPM‐A, with almost identical crystal data, and the only difference is that molecules in CPM‐A crystal take a little looser packing arrangement. X‐ray diffraction and cross‐polarization under magic spinning 13C NMR spectra double confirm that they are different crystals. Interestingly, CPM‐A crystal shows negligible RTP compared to the CPM crystal, once again proving that the packing style is critical to the RTP property.
Long‐lived room temperature phosphorescence (RTP) with lifetime up to 0.748 s is realized in a pure organic single crystal. Compact face to face packing style in the crystal is found to favor long RTP lifetime and high photoluminescent intensity. This finding reveals that the molecular packing can affect optical properties significantly.
Catalytic transformations involving metal carbenes are considered one of the most important aspects of homogeneous transition metal catalysis. Recently, gold-catalyzed generation of gold carbenes ...from readily available alkynes represents a significant advance in metal carbene chemistry. This Review summarizes the advances in the gold-catalyzed nitrene-transfer reactions of alkynes with nitrogen-transfer reagents, such as azides, nitrogen ylides, isoxazoles, and anthranils, and gold-catalyzed carbene-transfer reactions, involving oxygen atom-transfer reactions of alkynes with nitro compounds, nitrones, sulfoxides, and pyridine N-oxides, through the presumable α-imino gold carbene and α-oxo gold carbene intermediates, respectively. Gold-catalyzed processes are reviewed by highlighting their product diversity, selectivity, and applicability, and the mechanistic rationale is presented where possible.
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