Qian Peng

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Name: 彭谦

Organization: Institute of Chemistry, Chinese Academy of Sciences , China

Department:

Title: Associate Researcher/Associate Professor(PhD)

TOPICS

Material Chemistry

OLED

Organic Chemistry

OLED

Chemicals
References

Theoretical Investigations on the Roles of Intramolecular Structure Distortion versus Irregular Intermolecular Packing in Optical Spectra of 6T Nanoparticles

Co-reporter:Wenqiang Li, Qian Peng, Huili Ma, Jin Wen, Jing Ma, Linda A. Peteanu, and Zhigang Shuai

Chemistry of Materials March 28, 2017 Volume 29(Issue 6) pp:2513-2513

Publication Date(Web):January 23, 2017

DOI:10.1021/acs.chemmater.6b04210

It is of vital importance to theoretically understand unique nanoparticle size-tunable and excitation wavelength-dependent multiple optical properties in organic nanoparticles. In this work, we proposed a theoretical protocol to calculate the optical spectrum of the organic nanoparticles, which combines molecular dynamics (MD) simulation, the quantum mechanics/molecular mechanics (QM/MM) approach, and vibronic-coupled Frenkel exciton spectrum theory. By using the protocol, we explored the relationship between intramolecular structure distortion, irregular intermolecular packing, and optical spectra in α-sexithiophene nanoparticles. Two representative clusters cutting from the simulated amorphous nanoparticle were investigated and found to exhibit a blue shift for absorption and emission spectra compared to the solution, which is totally different from the blue-shifted absorption and red-shifted emission in crystal. For the cluster with distorted monomer and disordered packing, the blue shift results from the higher excitation energy and larger vibronic coupling of low-frequency vibration modes, while for the cluster with planar monomer and ordered packing, the blue shift is induced by the synergism of vibronic coupling and excitonic coupling. Strikingly, the superposition of the spectra of two clusters reproduces the experimental spectra and well explains the unusual blue-shifted emission observed for α-sexithiophene nanoparticles. Our theoretical protocol is general and applicable to other organic nanoparticles, thus aiding the rational design of high-quality organic nanoparticles.

Excitonic coupling effect on the nonradiative decay rate in molecular aggregates: Formalism and application

Co-reporter:Wenqiang Li, Lili Zhu, Qiang Shi, Jiajun Ren, Qian Peng, Zhigang Shuai

Chemical Physics Letters 2017 Volume 683(Volume 683) pp:

Publication Date(Web):1 September 2017

DOI:10.1016/j.cplett.2017.03.077

•An analytical nonradiative rate formalism is derived including excitonic coupling.•The nonradiative decay rate is enhanced by the coupling for both H- and J- aggregates.•Excitonic coupling effect is minor for the Aggregation-induced emission luminogens.We present here an analytical thermal vibration correlation function formalism to calculate the nonradiative decay rate constant (knr) considering excitonic coupling effect (ECE) for molecular aggregates based on split-operator approximation. Combining with first-principles calculations, we found that knr is enhanced by ECE for both H- and J-aggregates. In addition, ECE is found to be minor for the AIEgens (aggregation-induced emission luminogens).Download high-res image (77KB)Download full-size image

Using the isotope effect to probe an aggregation induced emission mechanism: theoretical prediction and experimental validation

Co-reporter:Tian Zhang, Qian Peng, Changyun Quan, Han Nie, Yingli Niu, Yujun Xie, Zujin Zhao, Ben Zhong Tang and Zhigang Shuai

Chemical Science 2016 vol. 7(Issue 8) pp:5573-5580

Publication Date(Web):11 May 2016

DOI:10.1039/C6SC00839A

Aggregation-induced emission (AIE) has become a hot topic for a variety of potential applications, but the understanding of its working mechanism is still under scrutiny. Herein, we proposed the use of the isotope effect (IE) to identify the AIE mechanism: under the restriction of an internal motion mechanism, the IE is pronouncedly different in excited-state decay rates when contrasting AIE luminogens (AIEgens) and non-AIEgens in theoretical calculations. For the complete deuteration of AIEgens, the IE of nonradiative decay rate in solution (<−10%) is much weaker than that (−65% to −95%) in aggregate, because the former stems from the overall results of competitive vibronic coupling and the severe mixing of low-frequency modes while the latter mainly comes from the vibronic coupling only. The experimental results confirm the isotopic “jump” behaviors in AIEgens well. However, non-AIEgens exhibit equivalent IEs (−40% to −90%) in both solution and solid phases. Further partial deuteration schemes for the 6-ring AIE analogues show positional dependence.

Supramolecular Structure-Dependent Thermally-Activated Delayed Fluorescence (TADF) Properties of Organic Polymorphs

Co-reporter:Yuewei Zhang, Huili Ma, Shipan Wang, Zhiqiang Li, Kaiqi Ye, Jingying Zhang, Yu Liu, Qian Peng, and Yue Wang

The Journal of Physical Chemistry C 2016 Volume 120(Issue 35) pp:19759-19767

Publication Date(Web):August 15, 2016

DOI:10.1021/acs.jpcc.6b05537

Electrostatic Interaction-Induced Room-Temperature Phosphorescence in Pure Organic Molecules from QM/MM Calculations

Co-reporter:Huili Ma; Wen Shi; Jiajun Ren; Wenqiang Li; Qian Peng;Zhigang Shuai

The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 15) pp:2893-2898

Publication Date(Web):July 14, 2016

DOI:10.1021/acs.jpclett.6b01156

Room temperature phosphorescence (RTP) from pure organic material is rare due to the low phosphorescence quantum efficiency. That is why the recent discovery of crystallization induced RTP for several organic molecules aroused strong interests. Through a combined quantum and molecular mechanics CASPT2/AMBER scheme taking terephthalic acid (TPA) as example, we found that electrostatic interaction not only can induce an enhanced radiative decay T1 → S0 through the dipole-allowed S1 intermediate state, but also can hinder the nonradiative decay process upon crystallization. From gas phase to crystal, the nature of S1 state is converted to 1(π,π*) from 1(n,π*) character, enhancing transition dipole moment and serving as an efficient intermediate radiative pathway for T1 → S0 transition, and eventually leading to a boosted RTP. The intermolecular packing also blocks the nonradiative decay channel of the high-frequency C═O stretching vibration with large vibronic coupling, rather than the conventional low-frequency aromatic rotation in crystal. This mechanism also holds for other organic compounds that contain both ketones and aromatic rings.

Spectroscopic Signature of the Aggregation-Induced Emission Phenomena Caused by Restricted Nonradiative Decay: A Theoretical Proposal

Co-reporter:Tian Zhang

The Journal of Physical Chemistry C 2015 Volume 119(Issue 9) pp:5040-5047

Publication Date(Web):February 16, 2015

DOI:10.1021/acs.jpcc.5b01323

It has been suggested that the exotic aggregation-induced emission (AIE) phenomenon was caused by the restriction on the nonradiative decay through intramolecular vibrational/rotational relaxation. There have been other proposed mechanisms such as J-aggregation or excimer formation, etc. Through computational studies, we propose a direct approach to verify the AIE process, namely, using resonance Raman spectroscopy (RRS) to explore the microscopic mechanism of AIE. Taking examples of AIE-active 1,2-diphenyl-3,4-bis(diphenylmethylene)-1-cyclobutene (HPDMCb) and AIE-inactive 2,3-dicyanopyrazino phenanthrene (DCPP) for comparison, we found that for the AIEgen, after aggregation into cluster, the intensities of low-frequency peaks in RRS are evidently reduced relative to the high-frequency peaks, along with a remarkable blueshift. However, the RRS of non-AIEgen remains almost unaffected upon aggregation. Such distinctive spectroscopic characteristics can be ascribed to the intramolecular vibrational relaxation which is hindered for AIEgen, especially for the low-frequency ring-twisting motions, because the RRS amplitude is proportional to the mode vibrational relaxation energy times frequency λjωj. Thus, RRS is a direct way to clarify the recent dispute on the AIE mechanism. If such predictions are true, it will clearly validate the earlier proposed restriction on the nonradiative decay through an intramolecular vibration/rotation relaxation mechanism.

Influences of Conjugation Extent on the Aggregation-Induced Emission Quantum Efficiency in Silole Derivatives: A Computational Study

Co-reporter:Yujun Xie;Tian Zhang; Zhen Li;Dr. Qian Peng;Dr. Yuanping Yi; Zhigang Shuai

Chemistry – An Asian Journal 2015 Volume 10( Issue 10) pp:2154-2161

Publication Date(Web):

DOI:10.1002/asia.201500303

Abstract

The photophysical properties of a series of silole derivatives, with hydrogen (TPS), bromine (BrTPS), and conjugated phenyl (HPS), triphenylsilyethynyl (BTPES), and dimethylfluorene (BFTPS) substituents at 2,5-positions in both gas and aggregate phases have been investigated computationally by employing the correlation function rate formalism coupled with a hybrid quantum/molecular mechanics (QM/MM) approach. It is found that the solid-state fluorescence quantum efficiency first increases sharply with the degree of π-conjugation of the 2,5-substituents, then levels off, and finally starts to decrease slightly. This is because the side-group conjugation tends to enhance the radiative decay rate in both gas and solid phases. However, a further increase in conjugation leads to saturation in the radiative decay rate but increases the non-raditiave decay rate due to the decreased energy gap.

SERS and NMR Studies of Typical Aggregation-Induced Emission Molecules

Co-reporter:Cheng Fang, Yujun Xie, Martin R. Johnston, Yinlan Ruan, Ben Zhong Tang, Qian Peng, and Youhong Tang

The Journal of Physical Chemistry A 2015 Volume 119(Issue 29) pp:8049-8054

Publication Date(Web):June 24, 2015

DOI:10.1021/acs.jpca.5b05478

Over recent decades, aggregation-induced emission (AIE) molecules have attracted increasing attention. Restriction of intramolecular rotation (RIR) has been widely accepted as the cause of the emission when AIE molecules aggregate into clusters. The intramolecular rotation of AIE molecules can be monitored by molecular vibration spectra such as nuclear magnetic resonance (NMR), infrared, and Raman, especially surface-enhanced Raman scattering (SERS) which has high sensitivity down to a single molecule. We employed SERS and NMR to study the AIE emission mechanism and compared experimental results with simulation data to monitor the RIR. Interestingly, we found that intramolecular rotation was also restricted for individual AIE molecules loaded onto SERS substrate surfaces due to the laid-down configuration.

Unusual Aggregation-Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion

Co-reporter:Fan Bu;Ruihong Duan;Yujun Xie;Dr. Yuanping Yi;Dr. Qian Peng;Dr. Rongrong Hu; Anjun Qin; Zujin Zhao; Ben Zhong Tang

Angewandte Chemie International Edition 2015 Volume 54( Issue 48) pp:14492-14497

Publication Date(Web):

DOI:10.1002/anie.201506782

Abstract

Aggregation-induced emission (AIE) is commonly observed for propeller-like luminogens with aromatic rotors and stators. Herein, we report that a coumarin derivative containing a seven-membered aliphatic ring (CD-7) but no rotors showed typical AIE characteristics, whereas its analogue with a five-membered aliphatic ring (CD-5) exhibited an opposite aggregation-caused quenching (ACQ) effect. Experimental and theoretical results revealed that a large aliphatic ring in CD-7 weakens structural rigidity and promotes out-of-plane twisting of the molecular backbone to drastically accelerate nonradiative excited-state decay, thus resulting in poor emission in solution. The restriction of twisting motion in aggregates blocks the nonradiative decay channels and enables CD-7 to fluoresce strongly. The results also show that AIE is a general phenomenon and not peculiar to propeller-like molecules. The AIE and ACQ effects can be switched readily by the modulation of molecular rigidity.

Unusual Aggregation-Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion

Co-reporter:Fan Bu;Ruihong Duan;Yujun Xie;Dr. Yuanping Yi;Dr. Qian Peng;Dr. Rongrong Hu; Anjun Qin; Zujin Zhao; Ben Zhong Tang

Angewandte Chemie 2015 Volume 127( Issue 48) pp:14700-14705

Publication Date(Web):

DOI:10.1002/ange.201506782

Abstract

Solvent Effects on the Optical Spectra and Excited-State Decay of Triphenylamine-thiadiazole with Hybridized Local Excitation and Intramolecular Charge Transfer

Co-reporter:Di Fan, Yuanping Yi, Zhendong Li, Wenjian Liu, Qian Peng, and Zhigang Shuai

The Journal of Physical Chemistry A 2015 Volume 119(Issue 21) pp:5233-5240

Publication Date(Web):November 17, 2014

DOI:10.1021/jp5099409

The triphenylamine-thiadiazole molecule (TPA-NZP) is a newly popular, highly efficient OLED fluorescent emitter with exciton utilization efficiency exceeding the upper limit of spin statistics (25%). In this work, the optical spectra and the radiative and nonradiative decay rate constants have been investigated theoretically for TPA-NZP in hexane, ethyl ether, tetrahydrofuran, and dimethylformamide solvents, in comparison with the gas phase. We observed the evolutions of the excited states from the hybridized local and charge-transfer (HLCT) character to complete intramolecular charge transfer (CT) character with the increase of the solvent polarities. It is found that upon increasing the solvent polarity, the amount of red shift in the absorption peak is much less than that of emission, resulting in breakdown of the mirror symmetry. This is because that 0–0 transition energy is red-shifted but the vibrational relaxation increases with the solvent polarity, leading to subtraction in absorption while addition in emission. The radiative decay rate constant is calculated to be almost independent of polarity. The nonradiative decay rate increases by almost one order of magnitude from that in nonpolar hexane to the strongly polarized dimethylformamide, which is attributed to the dual effects of the red shift in the gap and enhancement of the vibrational relaxation by solvent polarity.

Aggregation induced blue-shifted emission – the molecular picture from a QM/MM study

Co-reporter:Qunyan Wu, Tian Zhang, Qian Peng, Dong Wang and Zhigang Shuai

Physical Chemistry Chemical Physics 2014 vol. 16(Issue 12) pp:5545-5552

Publication Date(Web):2014/01/24

DOI:10.1039/C3CP54910K

In general, optical emission in the solid-state is red-shifted with respect to the solution phase. A series of recently synthesized compounds exhibits aggregation induced blue-shifted emission (AIBSE) phenomena. By employing a polarizable continuum model (PCM) and a hybrid quantum mechanics/molecular mechanics (QM/MM) approach, we investigate the excited-state electronic structures of some typical AIE-active molecules both in solvents and in aggregates at the time-dependent density functional theory (TD-DFT) level. It is found that the AIBSE phenomena originate from the smaller reorganization energy in aggregates than in the solution phase, as evidenced through the restricted structural relaxation, planarization in the excited state, and freezing of low-frequency out-of-plane twists in the transition state.

Aggregation Effects on the Optical Emission of 1,1,2,3,4,5-Hexaphenylsilole (HPS): A QM/MM Study

Co-reporter:Tian Zhang, Yuqian Jiang, Yingli Niu, Dong Wang, Qian Peng, and Zhigang Shuai

The Journal of Physical Chemistry A 2014 Volume 118(Issue 39) pp:9094-9104

Publication Date(Web):June 12, 2014

DOI:10.1021/jp5021017

We investigate the photophysical property for 1,1,2,3,4,5-hexaphenylsilole (HPS) through combined quantum mechanical and molecular mechanical (QM/MM) simulations. Under the displaced harmonic oscillator approximation with consideration of the Duschinsky rotation effect (DRE), the radiative and nonradiative rates of the excited-state decay processes for HPS are calculated by using the analytical vibration correlation function approach coupled with first-principles calculations. The intermolecular packing effect is incorporated through electrostatic interaction modeled by a force field. We find that from the gas phase to the solid state (i) the side phenyl ring at the 5-position becomes coplanar with the central silacycle, which increases the degree of conjugation, thus accelerating the radiative decay process, and (ii) the rotation of the side phenyl ring at the 2-position is restricted, which blocks the excited-state nonradiative decay channels. Such a synergetic effect largely enhances the solid-state luminescence quantum efficiency through reducing the nonradiative decay rate by about 4 orders of magnitude, leading to the radiative decay overwhelming the nonradiatvie decay. In addition, the calculated solid-phase absorption and emission optical spectra of HPS are found to be in agreement with the experiment.

Theoretical design of polythienylenevinylene derivatives for improvements of light-emitting and photovoltaic performances

Co-reporter:Yuqian Jiang, Qian Peng, Xing Gao, Zhigang Shuai, Yingli Niu and Sheng Hsien Lin

Journal of Materials Chemistry A 2012 vol. 22(Issue 10) pp:4491-4501

Publication Date(Web):12 Jan 2012

DOI:10.1039/C1JM14956C

Poly(thienylene vinylene) (PTV) is a low-bandgap polymer but shows poor performance in both light-emitting and photovoltaic applications. Recently a derivative of PTV with carboxylate substitution, poly(3-carboxylated thienylenevinylene) (P3CTV), has been synthesized and was shown to be fluorescent. The photovoltaic power conversion efficiency based on P3CTV has been found to be much larger than PTV, indicating an intrinsically concomitant relationship between light-emitting and photovoltaic properties. Employing quantum chemistry calculations coupled with our correlation function formalism for excited state decay and optical spectra, we have investigated a series of side-chain substituted PTVs targeting optimal optoelectronic performance. We predict that the carbonyl substituted PTV is a strongly fluorescent polymer with low bandgap, long exciton lifetime, and large spectral overlap between emission and absorption. It is expected that carbonyl PTV is a promising light-emitting and photovoltaic polymer. Methodology wise, we find that (i) our correlation function approach to calculate the optical spectrum has much lower computational scaling with respect to the system size than the conventional method; (ii) the harmonic oscillator approximation for the nonadiabatic decay works better for a large system than for a small system.

Pushing Fullerene Absorption into the Near-IR Region by Conjugately Fusing Oligothiophenes

Co-reporter:Dr. Zuo Xiao;Gang Ye;Ying Liu;Shan Chen;Dr. Qian Peng;Qiqun Zuo;Dr. Liming Ding

Angewandte Chemie 2012 Volume 124( Issue 36) pp:9172-9175

Publication Date(Web):

DOI:10.1002/ange.201203981

Pushing Fullerene Absorption into the Near-IR Region by Conjugately Fusing Oligothiophenes

Co-reporter:Dr. Zuo Xiao;Gang Ye;Ying Liu;Shan Chen;Dr. Qian Peng;Qiqun Zuo;Dr. Liming Ding

Angewandte Chemie International Edition 2012 Volume 51( Issue 36) pp:9038-9041

Publication Date(Web):

DOI:10.1002/anie.201203981

Excited states structure and processes: Understanding organic light-emitting diodes at the molecular level

Co-reporter:Zhigang Shuai, Qian Peng

Physics Reports (30 April 2014) Volume 537(Issue 4) pp:123-156

Publication Date(Web):30 April 2014

DOI:10.1016/j.physrep.2013.12.002

Photo- or electro-excited states in polyatomic molecules, aggregates, and conjugated polymers are at the center of organic light-emitting diodes (OLEDs). These can decay radiatively or non-radiatively, determining the luminescence quantum efficiency of molecular materials. According to Kasha’s rule, light-emission is dictated by the lowest-lying excited state. For conjugated polymers, the electron correlation effect can lead the lowest-lying excited state to the even-parity 2Ag state which is non-emissive. To understand the nature of the low-lying excited state structure, we developed the density matrix renormalization group (DMRG) theory and its symmetrization scheme for quantum chemistry applied to calculate the excited states structure. We found there are three types of 1Bu/2Ag crossover behaviors: with electron correlation strength U, with bond length alternation, and with conjugation length. These directly influence the light-emitting property.For the electro-excitation, carriers (electron and hole) are injected independently, forming both singlet and triplet excited bound states with statistically 25% and 75% portions, respectively. We found that the exciton formation rate can depend on spin manifold, and for conjugated polymers, the singlet exciton can have larger formation rate leading to the internal electroluminescence quantum efficiency larger than the 25% spin statistical limit. It is originated from the interchain electron correlation as well as intrachain lattice relaxation.For the dipole allowed emissive state, the radiative decay process via either spontaneous emission or stimulated emission can be computed from electronic structure plus vibronic couplings. The challenging issue lies in the non-radiative decay via non-adiabatic coupling and/or spin–orbit coupling. We developed a unified correlation function formalism for the excited state radiative and non-radiative decay rates. We emphasized the low-frequency mode mixing (Duschinsky rotation) effect on the non-radiative decay. We further combined the non-adiabatic coupling and spin–orbit coupling for the triplet state decay (phosphorescence) quantum efficiency. All the formalisms have been developed analytically, which have been applied to optical spectroscopy, aggregation-induced emission phenomena, and polymer photovoltaic property.

Aggregation induced blue-shifted emission – the molecular picture from a QM/MM study

Co-reporter:Qunyan Wu, Tian Zhang, Qian Peng, Dong Wang and Zhigang Shuai

Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 12) pp:NaN5552-5552

Publication Date(Web):2014/01/24

DOI:10.1039/C3CP54910K

Theoretical design of polythienylenevinylene derivatives for improvements of light-emitting and photovoltaic performances

Co-reporter:Yuqian Jiang, Qian Peng, Xing Gao, Zhigang Shuai, Yingli Niu and Sheng Hsien Lin

Journal of Materials Chemistry A 2012 - vol. 22(Issue 10) pp:NaN4501-4501

Publication Date(Web):2012/01/12

DOI:10.1039/C1JM14956C

Using the isotope effect to probe an aggregation induced emission mechanism: theoretical prediction and experimental validation

Co-reporter:Tian Zhang, Qian Peng, Changyun Quan, Han Nie, Yingli Niu, Yujun Xie, Zujin Zhao, Ben Zhong Tang and Zhigang Shuai