The Importance of Excited‐State Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives

Understanding excited‐state dynamics is critical for improving the photoluminescence (PL) efficiency of exciplexes. A series of exciplexes based on conventional hole‐transporting materials as donor and newly developed phenylpyridinato boron derivatives as acceptor were investigated. High PL efficiencies were achieved in only some combinations, and a large difference in performance among combinations provided insight into nonradiative processes in exciplex systems. Furthermore, the triplet local excited states (³LE) of each donor and acceptor were found play an important role in triplet exciplex harvesting. Significant contributions from triplets were clearly observed when the charge‐transfer excited states (¹CT and ³CT) and ³LE were ideally aligned. We also demonstrated fine control of relative energy alignment via the concentration to improve the PL efficiency.     

Manipulation of Molecular Aggregation States to Realize Polymorphism,AIE, MCL,and TADF in a Single Molecule

Multifunctional emitting materials are scarce and need to be further explored. Now, a newly anthraquinone derivative, 2‐(phenothiazine‐10‐yl)‐anthraquinone (PTZ‐AQ) was designed and synthesized and found to demonstrate polymorphism, multi‐color emission, aggregation‐induced emission (AIE), mechanochromic luminescence (MCL), and thermally activated delayed fluorescence (TADF) in its different solid forms. It is shown for the first time that TADF properties of a compound can be systematically tuned via its aggregation state. The optimized PTZ‐AQ crystal shows a small singlet–triplet energy splitting of 0.01 eV and exhibits red TADF with a photoluminescence quantum yield as high as 0.848. This study shows that the unique multiple functions can be integrated into one single compound through controlling the aggregation states, which provides a new strategy for the investigation and application of multifunctional organic materials.     

Fluorescence and Time-Resolved Delayed Luminescence of Porphyrins in Organic Solvents and Polymer Matrices

Porphyrin dyes fulfill an essential function in photosynthesis and are important in photodynamic therapy and in a range of electronic devices. Their spectroscopic characteristics may play a crucial role in these processes. The spectral properties of two porphyrin dyes: tetraphenylporphyrin and tetraphenysulfporphyrin in organic solvents (acetone, chloroform, methyl alcohol, and dimethyl-sulfoxide) and in polyvinyl alcohol and poly(methylmethacrylate) films have been investigated. Absorption, fluorescence, and microsecond time-resolved delayed luminescence spectra have been measured at room temperature. The existence of different aggregated dye forms in the ground and excited states has been demonstrated. The manifold of dye species depends on the solvent/polymer. In the case of the polymers, it also depends on the solvent used to coat the polymer film. Delayed luminescence spectra and decay times of the two porphyrins in the different solutions and in polymeric matrices suggest that different mechanisms of deexcitation of the singlet excited states may be responsible for their generation in these and other porphyrin dyes.     

多共振热激活延迟荧光过程的理论研究

本工作借助第一性原理和动力学演化,系统地研究了四个叔丁基-咔唑及吩噻嗪取代的硼-氮化合物(BCz-BN、2PTZ-BN、Cz-PTZ-BN和2Cz-PTZ-BN)的多共振热激活延迟荧光的高效发光机制.结果表明上述分子T₁与T₂间的内转换速率远大于其它辐射与非辐射速率,同时T₂到S₁的反向系间窜越速率也高于T₁到S₁的反向系间窜越速率,因此其多共振热激活延迟荧光过程应遵循T₁→T₂→S₁→S₀的路径.进一步动力学演化表明,T₁与T₂之间的内转换主要发生在演化初期,随着时间的推移,能量逐渐由T₂向S₁转移,并最终在S₁完成荧光发射.上述研究揭示了多共振延迟荧光的微观本质,为未来设计及合成新的多共振热激活延迟荧光分子提供了理论依据.     

Small deviations of series of independent positive random variables with weights close to exponential

Let ξ, ξ₀, ξ₁, ... be independent identically distributed (i.i.d.) positive random variables. The present paper is a continuation of the article [1] in which the asymptotics of probabilities of small deviations of series S = Σ _j=0 ^∞ a(j)ξ _j was studied under different assumptions on the rate of decrease of the probability ?(ξ < x) as x → 0, as well as of the coefficients a(j) ≥ 0 as j → ∞. We study the asymptotics of ?(S < x) as x → 0 under the condition that the coefficients a(j) are close to exponential. In the case when the coefficients a(j) are exponential and ?(ξ < x) ～ bx ^α as x → 0, b > 0, a > 0, the asymptotics ?(S < x) is obtained in an explicit form up to the factor x ^o(1). Originality of the approach of the present paper consists in employing the theory of delayed differential equations. This approach differs significantly from that in [1].     

一类时滞多组传染病模型的全局稳定性分析

本文研究具有变量分离发生率的具时滞的多组传染病模型.首先,分别针对强连通和非强连通情形,得到基本再生数$R_0$. 然后运用Lyapunov泛函方法和LaSalle不变集原理分别分析了当$R_0<1$时无病平衡点$P_0$ 的全局渐近稳定性以及$R_0>1$时地方病平衡点$P^*$的全局渐近稳定性.     

Adaptive impulsive synchronization of uncertain delayed chaotic system with full unknown parameters via discrete‐time drive signals

This article investigates the adaptive impulsive synchronization of delayed chaotic system with full unknown parameters. Aiming at this problem, we propose a new adaptive strategy, in which both the adaptive–impulsive controller and the parameters adaptive laws are designed via the discrete‐time signals from the drive system. The corresponding theoretical proof is given to guarantee the effectiveness of the proposed strategy. Moreover, the concrete adaptive strategies are achieved for delayed Hopfield neural network, optical Ikeda system and the well‐known delayed Lü chaotic system. As expected, numerical simulations show the effectiveness of the proposed strategy. This method has potential applications in parameters estimation, secure communication, and cryptanalysis when only discrete signals are transmitted in communication channel. © 2014 Wiley Periodicals, Inc. Complexity 21: 43–51, 2016     

Synchronization of fractional‐order delayed neural networks with hybrid coupling

This article presents new theoretical results on the synchronization for a class of fractional‐order delayed neural networks with hybrid coupling that contains constant coupling and discrete‐delay coupling. This is the first attempt to investigate the synchronization problem of fractional‐order coupled delayed neural networks. Based on the fractional‐order Lyapunov stability theorem and Kronecker product properties, sufficient criteria are established to ensure the fractional‐order coupled neural network to achieve synchronization. Numerical simulations are given to illustrate the correctness of the theoretical results. © 2015 Wiley Periodicals, Inc. Complexity 21: 106–112, 2016     

Stability and Hopf bifurcation analysis of novel hyperchaotic system with delayed feedback control

In this article, a novel four dimensional autonomous nonlinear systezm called hyperchaotic Rikitake system is proposed. Basic properties of the new system are investigated and the complex dynamical behaviors, such as time series, bifurcation diagram, and Lyapunov exponents are analyzed by dynamic analysis approaches. To control the new hyperchaotic system, the delayed feedback control is introduced. Regarding the time delay as a bifurcation parameter, stability and bifurcations with respect to time delay are investigated. Conditions assuring the existence of Hopf bifurcation and the distribution of roots to the associated characteristic equation are investigated by utilizing the polynomial theorem. Besides, the Hopf bifurcation is proved to occur when the bifurcation parameter (time delay) crosses through derived critical value. Finally, numerical simulations are provided to prove the consistence with the derived theoretical results. © 2015 Wiley Periodicals, Inc. Complexity 21: 180–193, 2016     

延迟有限理性下推测变差寡头博弈模型的复杂性

在参与人具有延迟有限理性决策下,构造含有伯川德推测变差的动态寡头模型,对模型的推测变差均衡点的存在性和唯一性进行了证明,把企业的产量调整速度作为变量,分析企业的产量调整速度的变化产生的周期分岔、混沌等复杂行为,并对比了延迟理性和DFC方法的混沌控制效果.研究表明,尽管二者作用机理不同,但混沌现象都发生了延迟甚至消失,即系统的稳定性增强.