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Organic light-emitting diodes:theoretical understanding of highly efficient materials and development of computational methodology

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National Science Review 2017年第2期4卷 224-239页

作者： zhigang shuai Qian Peng MOE Key Laboratory of Organic Optoelectronics and Molecular Engineering Department of ChemistryTsinghua University CAS Key Laboratory of Organic Solids Institute of ChemistryChinese Academy of Sciences

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.

关键词： excited-state theory organic electroluminescence spin statistics quantum efficiency vibration correlation function

Molecular mechanism of aggregation-induced emission

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Aggregate 2021年第5期2卷 151-170页

作者： Qian Peng zhigang shuai School of Chemical Sciences University of Chinese Academy of SciencesBeijingChina Kay Laboratory of Organic Solids and Beijing National Laboratory for Molecular Science Institute of ChemistryChinese Academy of SciencesBeijingChina MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering Department of ChemistryTsinghua UniversityBeijingChina

Deep understanding of the inherent luminescence mechanism is essential for the development of aggregation-induced emission(AIE)materials and *** 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 ***,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 *** 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 *** 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 *** theoretical work not only justifies a plethora of experimental results but also makes reliable predictions on molecular design and mechanism that can be experimentally *** 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.

关键词： aggregation-induced emission dipole-allowed bright state minimum energy crossing point nonradiative decay vibration relaxation

Effects of charge distribution on water filling process in carbon nanotube

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Science China Chemistry 2009年第2期52卷 137-143页

作者： MENG LingYi LI QiKai shuai zhigang Beijing National Laboratory for Molecular Sciences and Key Laboratory of Organic Solids Institute of ChemistryChinese Academy of SciencesBeijing 100190China Department of Chemistry Tsinghua UniversityBeijing 100084China

Using umbrella sampling technique with molecular dynamics simulation,we investigated the nanoflu-idic transport of water in carbon nanotube(CNT).The simulations showed that a positive charge modi-fication to the carbon nanotube can slow down the water column growth process,while the negative charge modification to the carbon nanotube will,on the other hand,quicken the water column growth *** free energy curves were obtained through the statistical process of water column growth under different charge distributions,and the results indicated that these free energy curves can be employed to explain the dynamical process of water column growth in the nanosized channels.

关键词： nanotube micro/nanofluidic molecular dynamics

Promoting-mode free formalism for excited state radiationless decay process with Duschinsky rotation effect

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Science China Chemistry 2008年第12期51卷 1153-1158页

作者： NIU YingLi PENG Qian shuai zhigang Key Laboratory of Organic Solids Beijing National Laboratory for Molecular Sciences(BNLMS)Institute of ChemistryChinese Academy of SciencesBeijing 100190China Department of Chemistry Tsinghua UniversityBeijing 100084China

In the present work, through the path integral of Gaussian type correlation function, a new formalism based on Fermi-Golden Rule for calculating the rate constant of nonradiative decay process with Duschinsky rotation effect in polyatomic molecules is developed. The advantage of the present path-integral formalism is promoting-mode free. In order to get the rate constant, a "transition rate matrix" needs to be calculated. The rate constant calculated previously is only an approximation of diagonal elements of our "transition rate matrix " . The total rate should be the summation over all the matrix elements.

关键词： Duschinsky rotation radiationless decay correlation function path integral promoting-mode free

From electronic excited state theory to the property predictions of organic optoelectronic materials

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Science China Chemistry 2013年第9期56卷 1277-1284页

作者： shuai zhigang XU Wei PENG Qian GENG Hua MOE Key Laboratory of Organic Optoelectronics and Molecular Engineering Department of ChemistryTsinghua University Key Laboratory of Organic Solids Beijing National Laboratory for Molecular ScienceInstitute of ChemistryChinese Academy of Sciences

We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.

关键词： electron dynamics methods statistical physics approaches light-emitting efficiency charge mobility exciton diffusion

The role of acoustic phonon scattering in charge transport in organic semiconductors:a first-principles deformation-potential study

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Science China Chemistry 2009年第10期52卷 1646-1652页

作者： TANG Ling LONG MengQiu WANG Dong shuai zhigang Department of Chemistry Tsinghua UniversityBeijing 100084China Key Laboratory of Organic Solids Beijing National Laboratory for Molecular ScienceInstitute of ChemistryChinese Academy of SciencesBeijing 100190China

The electron-acoustic phonon scattering for charge transport in organic semiconductors has been studied by first-principles density functional theory and the Boltzmann transport equation with relaxation time approximation. Within the framework of deformation-potential theory, the electron-longitudinal acoustic phonon scattering probability and the corresponding relaxation time have been obtained for oligoacene single crystals (naphthalene, anthracene, tetracene and pentacene). Previously, the electron-optic phonon scattering mechanism has been investigated through Holstein-Peierls model coupled with DFT calculations for naphthalene. Numerical results indicate that the acoustic phonon scattering intensity is about 3 times as large as that for the optic phonon and the obtained mobility is in much better agreement with the result of the experiment done for ultrapure single crystals. It is thus concluded that for closely packed molecular crystal where the electron is partly delocalized, acoustic phonon scattering mechanism prevails in the charge transport. Moreover, it is found that the intrinsic electron mobility is even larger than hole mobility. A frontier orbital overlap analysis can well rationalize such behavior.

关键词： mobility acoustic phonon scattering Boltzmann equation organic materials

Strain induced polymorphism and band structure modulation in low-temperature 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene single crystal

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Science China Chemistry 2017年第2期60卷 275-283页

作者： Jianfeng Chen Wen Shi Yuqian Jiang Dong Wang zhigang shuai MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering Department of ChemistryTsinghua UniversityBeijing 100084China National Center for Nanoscience and Technology Beijing 100190China Key Laboratory of Organic Solids Beijing National Laboratory for Molecular Science(BNLMS)Institute of ChemistryChinese Academy of SciencesBeijing 100190China Collaborative Innovation Center of Chemistry for Energy Materials Xiamen UniversityXiamen 351005China

Organic semiconductors are inherently soft,making it possible to increase their mobilities by *** a unique feature can be exploited directly in flexible electronics for improved device *** 2,7-dioctyl[1]benzothieno[3,2-b][1]-benzothiophene derivative,C8-BTBT is one of the best small-molecule hole transport ***,we demonstrated its band structure modulation under strains by combining the non-equilibrium molecular dynamics simulations and first-principles *** found that the C8-BTBT lattice undergoes a transition from monoclinic to triclinic crystal system at the temperature below 160 *** shear and uniaxial strains were applied to the low-temperature triclinic phase of C8-BTBT,and polymorphism was identified in the shear *** band width enhancement is up to 8%under 2%of compressive strain along the x direction,and 14%under 4%of tensile strain along the y *** band structure modulation of C8-BTBT can be well related to its herringbone packing motifs,where the edge to face and edge to edge pairs constitute two-dimensional charge transport pathways and their electronic overlaps determine the band widths along the two directions *** findings pave the way for utilizing strains towards improved performance of organic semiconductors on flexible substrates,for example,by bending the substrates.

关键词： charge transport shear strain polymorphism band structure modulation flexible electronics

Substituent-controlled aggregate luminescence:Computational unraveling of S_(1)/S_(0)surface crossing

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Aggregate 2023年第3期4卷 110-119页

作者： Ping-An Yin Qi Ou Qian Peng zhigang shuai MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering Department of ChemistryTsinghua UniversityBeijingChina AI for Science Institute BeijingChina School of Chemical Science University of Chinese Academy of SciencesBeijingChina School of Science and Engineering The Chinese University of Hong KongShenzhenGuangdongChina

We computationally investigated the molecular aggregation effects on the excited state deactivation processes by considering both the direct vibrational relaxation and the S0/S1 surface crossing,that is,the minimum energy conical intersection(MECI).Taking classical AIEgens bis(piperidyl)anthracenes(BPAs)isomers and the substituted silole derivatives as examples,we show that the deformation ofMECI always occurs at the atom with greater hole/electron ***,the energetic and structural changes of MECI caused by substituent has been *** find that effective substituent such as the addition of the electron-donating groups,which can polarize the distribution of hole/electron density of molecules,will lead to the pyramidalization deformation of MECI occurring at the substituent position and simultaneously reduce the required energy to reach *** MECI is sterically restricted by the surrounding molecules in solid phase,which remarkably hinders the non-radiative decay through surface *** quantitative computational assessments of the fluorescence quantum efficiency for both solution and solid phases,we elucidate the role of MECI and its dependence on the substitutions through pyramidalization deformation,which give rise to the aggregation-induced emission(AIE)phenomenon for 9,10-BPA,to aggregation-enhance emission(AEE)behavior for 1,4-BPA,and to conventional aggregation-caused quenching(ACQ)for 1,*** further verify such mechanism for siloles,for which we found that the substitutions do not change the AIE *** findings render a general molecular design approach to manipulating the aggregation effect for optical emission.

关键词： aggregation-caused quenching aggregation-induced emission minimum energy conical intersection substituent effect

Simultaneous studies of pressure effect on charge transport and photophysical properties in organic semiconductors:A theoretical investigation

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Chinese Chemical Letters 2021年第3期32卷 1233-1236页

作者： Xueying Lu Yajing Sun Zhicheng Zhang zhigang shuai Wenping Hu Tianjin Key Laboratory of Molecular Optoelectronic Sciences Department of ChemistrySchool of ScienceTianjin UniversityTianjin 300072China MOE Key Laboratory of Organic Optoelectronics and Molecular EngineeringDepartment of ChemistryTsinghua UniversityBeijing 100084China

High-mobility and strong luminescent materials are essential as an important component of organic photodiodes,having received extensive attention in the field of organic *** the conventional chemical synthesis of new molecules,pressure technology,as a flexible and efficient method,can tune the electronic and optical properties ***,the mechanism in organic materials has not been systematically ***,we theoretically predicted the pressure-depended luminescence and charge transport properties of high-performance organic optoelectronic semiconductors,2,6-diphenylanthracene(DPA),by first-principle and multi-scale theoretical calculation *** dispersion-corrected density functional theory(DFT-D)and hybrid quantum mechanics/molecular mechanics(QM/MM)method were used to get the electronic structures and vibration properties under ***,the charge transport and luminescence properties were calculated with the quantum tunneling method and thermal vibration correlation *** found that the pressure could significantly improve the charge transport performance of the DPA single *** the applied pressure increased to 1.86 GPa,the hole mobility could be *** the same time,due to the weak exciton coupling effect and the rigid flat structure,there is neither fluorescence quenching nor obvious emission enhancement *** DPA single crystal possesses a slightly higher fluorescence quantum yield~0.47 under *** work systematically explored the pressure-dependence photoelectric properties and explained the inside ***,we proposed that the exte rnal pressure would be an effective way to improve the photoelectric perfo rmance of organic semiconductors.

关键词： Pressure effect Organic semiconductors Charge transport properties Fluorescence quantum yield Density functional theory Multi-scale theoretical calculation