Zhigang Shuai

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Organization: Institute of Chemistry

Department: Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science

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Material Chemistry

OLED

Organic Chemistry

OLED

Chemicals
References

Modeling thermoelectric transport in organic materials

Co-reporter:Dong Wang, Wen Shi, Jianming Chen, Jinyang Xi and Zhigang Shuai

Physical Chemistry Chemical Physics 2012 vol. 14(Issue 48) pp:16505-16520

Publication Date(Web):06 Sep 2012

DOI:10.1039/C2CP42710A

Thermoelectric energy converters can directly convert heat to electricity using semiconducting materials via the Seebeck effect and electricity to heat via the Peltier effect. Their efficiency depends on the dimensionless thermoelectric figure of merit of the material, which is defined as zT = S2σT/κ with S, σ, κ, and T being the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature respectively. Organic materials for thermoelectric applications have attracted great attention. In this review, we present our recent progress made in developing theories and computational schemes to predict the thermoelectric figure of merit at the first-principles level. The methods have been applied to model thermoelectric transport in closely-packed molecular crystals and one-dimensional conducting polymer chains. The physical insight gained in these studies will help in the design of efficient organic thermoelectric materials.

Multifunctional bipolar triphenylamine/oxadiazole derivatives: highly efficient blue fluorescence, red phosphorescence host and two-color based white OLEDs

Co-reporter:Youtian Tao, Qiang Wang, Yuan Shang, Chuluo Yang, Liang Ao, Jingui Qin, Dongge Ma and Zhigang Shuai

Chemical Communications 2009 (Issue 1) pp:77-79

Publication Date(Web):20 Nov 2008

DOI:10.1039/B816264F

Two simple triphenylamine/oxadiazole derivatives were synthesized and fully characterized; their multifunctionality as highly efficient non-doped blue fluorescence, excellent red phosphorescent host and single-doped two-color based white OLEDs has been demonstrated.

Influences of Crystal Structures and Molecular Sizes on the Charge Mobility of Organic Semiconductors: Oligothiophenes

Co-reporter:Xiaodi Yang, Linjun Wang, Caili Wang, Wei Long and Zhigang Shuai

Chemistry of Materials 2008 Volume 20(Issue 9) pp:3205

Publication Date(Web):April 11, 2008

DOI:10.1021/cm8002172

Both crystal packing and molecular size have strong influences on the charge mobility for organic semiconductors. The crystal structures for oligothiophene (nT) can be roughly classified into two types: the Z = 2 (two molecules in one unit cell) or high temperature (HT) phase and the Z = 4 or low temperature (LT) phase. Through first-principles calculations within the Marcus electron transfer theory coupled with random walk simulation for room temperature charge diffusion constants, we found that the hole mobility of the HT phase is about 3–4 times larger than that of the LT phase because the molecular packing in the HT phase favors the hole transfer (i.e., the frontier orbital wave function phases of the dimer are constructive, which tends to maximize the overlap), while for the LT phase, the molecules are packed in a position that reduces the intermolecular orbital overlap due to phase cancellation. As the molecular size increases from 2T to 8T, the hole mobility tends to increase because the reorganization energy decreases with the chain length.

Theoretical comparative studies of charge mobilities for molecular materials: Pet versus bnpery

Co-reporter:Caili Wang, Fuhe Wang, Xiaodi Yang, Qikai Li, Zhigang Shuai

Organic Electronics 2008 Volume 9(Issue 5) pp:635-640

Publication Date(Web):October 2008

DOI:10.1016/j.orgel.2008.04.003

Charge mobility is the most important issue for organic semiconductors. We calculate the electron and hole mobilities for prototypical polycyclic hydrocarbon molecules, perylothiophene (pet) and benzo(g,h,i)-perylene (bnpery) using Marcus electron transfer theory coupled with a diabatic model and a homogeneous diffusion assumption to obtain the charge mobility. The first-principles DFT calculations show that the hole mobility is about an order of magnitude higher than the electron mobility in pet. However, we find that for bnpery, the electron and hole transports are balanced, namely, very close in mobility, indicating the possible application in light-emitting field-effect transistor. The crystal packing effects on the frontier orbital coupling are found to be essential to understand such differences in transport behaviors.

Theoretical Designs of Molecular Photonics Materials

Co-reporter:Yuanping Yi;Lingyun Zhu

Macromolecular Theory and Simulations 2008 Volume 17( Issue 1) pp:12-22

Publication Date(Web):

DOI:10.1002/mats.200700054

Theoretically Rational Designs of Transport Organic Semiconductors Based on Heteroacenes

Co-reporter:Yuan-Hang HE;Ren-Jie HUI;Yuan-Ping YI;Zhi-Gang SHUAI

Chinese Journal of Chemistry 2008 Volume 26( Issue 6) pp:1005-1010

Publication Date(Web):

DOI:10.1002/cjoc.200890179

Abstract

A Marcus electron transfer theory coupled with an incoherent polaron hopping and charge diffusion model in combining with first-principle quantum chemistry calculation was applied to investigating the effects of heteroatom on the intermolecular charge transfer rate for a series of heteroacene molecules. The influences of intermolecular packing and charge reorganization energy were discussed. It was found that the sulphur and nitrogen substituted heteroacenes were intrinsically hole-transporting materials due to the reduced hole reorganization energy and the enhanced overlap between HOMOs. For the oxygen-substituted heteroacene, it was found that both the electronic couplings and the reorganization energies for holes and electrons were comparative, indicating the application potential of ambipolar devices. Most interestingly, for the boron-substituted heteroacenes, theoretical calculations predicted a promising electron-transport material, which is rare for organic materials. These findings provide insights into rationally designing organic semiconductors with specific properties.

Local configuration interaction single excitation approach: Application to singlet and triplet excited states structure for conjugated chains

Co-reporter:Qingxu Li, Qikai Li, Zhigang Shuai

Synthetic Metals 2008 Volume 158(8–9) pp:330-335

Publication Date(Web):June 2008

DOI:10.1016/j.synthmet.2008.02.002

A local configuration interaction single (LCIS) excitations approach is implemented and applied to investigate the electronic excited states of extended conjugated polyenes up to 400 carbons within the semi-empirical Pariser–Parr–Pople (PPP) model. Numerical results show that the LCIS approach can reproduce well the canonical CIS results with much less computational costs. The dimension of the Hamiltonian matrix scales linearly in LCIS approach, comparing to quadratic scaling with canonical orbitals. Calculations for the lowest singlet excitation energy and the singlet–triplet splittings up to system with 400 carbons are demonstrated to saturate at about 100 carbons for polyene chain.

Electron correlation effects on the nonlinear optical properties of conjugated polyenes

Co-reporter:Qingxu Li, Liping Chen, Qikai Li, Zhigang Shuai

Chemical Physics Letters 2008 Volume 457(1–3) pp:276-278

Publication Date(Web):20 May 2008

DOI:10.1016/j.cplett.2008.04.020

Abstract

We employ the coupled cluster method to calculate the nonlinear optical coefficients for conjugated polyenes and their push–pull forms. We find that the electron correlation always reduces the nonlinear optical responses. While MP2 can predict correct trend for properties like dipole moment and polarizability, it gives completely wrong trend for the hyperpolarizabilites for long polyenes. It is highly cautioned to use MP2 when benchmarking computational methods for nonlinear properties such as improving exchange-correlation functionals in DFT.

Multiphoton Absorption in Expanded Porphyrins

Co-reporter:Yuanhang He, Renjie Hui, Yuanping Yi, Zhigang Shuai

Acta Physico-Chimica Sinica 2008 Volume 24(Issue 4) pp:565-570

Publication Date(Web):April 2008

DOI:10.1016/S1872-1508(08)60023-6

We have calculated the multiphoton absorption cross-sections for three expanded porphyrin derivatives using the sum-over-states-involved tensor approach in combination with the strongly correlated multireference determinant single- and double-configuration interaction method. The calculated results showed that the two- and three-photon energies corresponding to the first peak of the multiphoton absorption spectra showed a decrease (red-shifted) with the number of inserted thiophene groups, whereas the cross sections showed a remarkable increase, particularly for three-photon absorption cross-section. However, the larger twist of the molecular plane for the expanded molecule resulted in an obvious drop in the increasing trend for three-photon absorption cross-section.

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

Co-reporter:YingLi Niu;Qian Peng

Science China Chemistry 2008 Volume 51( Issue 12) pp:1153-1158

Publication Date(Web):2008 December

DOI:10.1007/s11426-008-0130-4

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.

An Ultra Closely π-Stacked Organic Semiconductor for High Performance Field-Effect Transistors

Co-reporter:H. Li;L. Li;Q. Tang;X. Yang;Y. Song;W. Xu;Y. Liu;Z. Shuai;W. Hu;D. Zhu

Advanced Materials 2007 Volume 19(Issue 18) pp:2613-2617

Publication Date(Web):14 AUG 2007

DOI:10.1002/adma.200700682

High performance organic thin-film transistors were demonstrated based on a cheap, commercially available organic semiconductor, titanyl phthalocyanine (TiOPc), in its α-phase structure. The high performance is due to its ultra close π-stack and favorable edge-on molecular orientation in the films. The high performance, the remarkable stability, low price, nontoxicity, and commercial availability of TiOPc suggest promising prospects in OTFTs.

Tuning the Energy Level and Photophysical and Electroluminescent Properties of Heavy Metal Complexes by Controlling the Ligation of the Metal with the Carbon of the Carbazole Unit

Co-reporter:C. L. Yang;X. W. Zhang;H. You;L. Y. Zhu;L. Q. Chen;L. N. Zhu;Y. T. Tao;D. G. Ma;Z. G. Shuai;J. G. Qin

Advanced Functional Materials 2007 Volume 17(Issue 4) pp:

Publication Date(Web):24 JAN 2007

DOI:10.1002/adfm.200600663

Four novel Ir^III and Pt^II complexes with cyclometalated ligands bearing a carbazole framework are prepared and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction studies of complexes 1, 3, and 4 reveal that the 3- or 2-position C atom of the carbazole unit coordinates to the metal center. The difference in the ligation position results in significant shifts in the emission spectra with the changes in wavelength being 84 nm for the Ir complexes and 63 nm for the Pt complexes. The electrochemical behavior and photophysical properties of the complexes are investigated, and correlate well with the results of density functional theory (DFT) calculations. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ₃/LiF/Al can attain very high efficiencies.

Theoretical study of inelastic X-ray scattering spectra for organic materials: Molecular excitation coupled with molecular exciton descriptions

Co-reporter:Li Ping Chen, Yuanping Yi, Qikai Li, Zhigang Shuai, Ke Yang, Dong Lai Feng

Synthetic Metals 2007 Volume 157(16–17) pp:670-677

Publication Date(Web):August 2007

DOI:10.1016/j.synthmet.2007.07.003

Inelastic X-ray scattering (IXS) spectrum provides a powerful tool to investigate the electronic structure of organic materials, in complimentary to the conventional optical spectra. Starting from a single molecule, then a dimer, and finally a cluster of molecular aggregate, we developed a Frenkel exciton model to describe the IXS process based on the quantum chemical calculations for the molecular excitations in the organic crystal of open-ring photomerocyanine form of spirooxazine (Py-SO). It is shown that the quantum chemical calculation combined with Frenkel exciton model can well describe the experimental measurements in terms of (i) the overall features of the IXS spectra from 2 to 10 eV, (ii) the dispersion behavior of the lowest exciton band, and (iii) the momentum-transfer dependence of the peak intensity. The roles of molecular excited state and the intermolecular interactions have been discussed for the IXS spectra.

Quantum Chemical Investigations on Electron Transport Characteristics of Porphyrin and Metal-porphyrin*

Co-reporter:Sheng-de OUYANG, Yuan-ping YI, Hua GENG, Zhi-gang SHUAI, Yi LUO

Chemical Research in Chinese Universities 2007 Volume 23(Issue 1) pp:87-91

Publication Date(Web):January 2007

DOI:10.1016/S1005-9040(07)60017-8

Localized electronic states in -layer-based superlattices with structural defects

Co-reporter:Wei-Qing Huang, Ke-Qiu Chen, Z. Shuai, Lingling Wang, Wangyu Hu, B.S. Zuo

Physica E: Low-dimensional Systems and Nanostructures 2005 Volume 28(Issue 4) pp:374-384

Publication Date(Web):September 2005

DOI:10.1016/j.physe.2005.04.012

Using an effect-barrier height method, we study the properties of the localized electronic states in an NN-layer-based superlattice with structural defects within the framework of effective-mass theory. The coupling effect between normal and lateral degrees of freedom of an electron on the localized electronic states in both symmetric and asymmetric triple layer superlattices with structural defects has been considered numerically. The results show that the localized states display different behaviors in both symmetric and asymmetric structures in spite of the minibands being not influenced by the structural symmetry. Moreover, the coupling effect causes the minibands, minigaps and localized electron levels to depend on the transverse wave number kxykxy. A brief physical analysis is given.

Charge-Transport Behavior in Aligned Carbon Nanotubes: A Quantum-Chemical Investigation

Co-reporter:X. Yang;L.-P. Chen;Z.-G. Shuai;Y.-Q. Liu;D.-B. Zhu

Advanced Functional Materials 2004 Volume 14(Issue 3) pp:

Publication Date(Web):10 MAR 2004

DOI:10.1002/adfm.200304481

Correlated quantum-chemical calculations are applied to analyze the amplitude of the electronic-transfer integrals that describe charge transport in interacting carbon nanotubes (CNTs) by investigating the influences of: i) the relative positions of the CNTs, ii) the size of the CNTs, and iii) their chemical impurities. Our results indicate that the mobility of the charge carrier is extremely sensitive to the molecular packing and the presence of chemical impurities. The largest splitting for the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels is in the case of perfectly cofacial conformations where hexagons face hexagons in the dimer structure. We found that the diameter of the CNT determines the type of transporting carrier: for CNTs with large diameters hole transport dominates, while for thin CNTs electron transport dominates. In general, the carrier mobility for the perfect CNTs (n ≥ 3) is less pronounced than that of C₆₀ due to their relatively small strain. B- and N-doped CNTs exhibit considerably larger mobilities owing to the possibility of metallic behavior. These results provide a plausible explanation for the high mobility found experimentally in a field-effect transistor (FET) made from a large-area, well-aligned CNT array. In addition, these hole-rich and electron-rich dopants imply potential applications in nanoelectronics.

Charge-transfer states and white emission in organic light-emitting diodes: a theoretical investigation

Co-reporter:Yan Fang, Shengli Gao, Xia Yang, Z Shuai, D Beljonne, J.L Brédas

Synthetic Metals 2004 Volume 141(1–2) pp:43-49

Publication Date(Web):18 March 2004

DOI:10.1016/j.synthmet.2003.09.022

Efficient white light emission has been recently reported in an electroluminescent device where the active material is a complex made of N,N′-bis(α-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and a boron–fluorine derivative of 1,6-bis(2-hydroxy-5-methylphenyl)pyridine ((mdppy)BF). Here, we investigate theoretically the intermolecular charge transfer in the materials. The interfacial layer is modeled on the basis of a simple dimer structure, for which the lowest excited states are described in the framework of a correlated quantum-chemical semiempirical technique. From the analysis of the calculated excited-state wavefunctions, we find that the lowest excited state possesses significant contributions from charge-transfer excitations from the donor (NPB) to the acceptor ((mdppy)BF). The influence of intermolecular distance and medium polarization are also explored.

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.

Multifunctional bipolar triphenylamine/oxadiazole derivatives: highly efficient blue fluorescence, red phosphorescence host and two-color based white OLEDs

Co-reporter:Youtian Tao, Qiang Wang, Yuan Shang, Chuluo Yang, Liang Ao, Jingui Qin, Dongge Ma and Zhigang Shuai

Chemical Communications 2009(Issue 1) pp:NaN79-79

Publication Date(Web):2008/11/20

DOI:10.1039/B816264F

Modeling thermoelectric transport in organic materials

Co-reporter:Dong Wang, Wen Shi, Jianming Chen, Jinyang Xi and Zhigang Shuai

Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 48) pp:NaN16520-16520

Publication Date(Web):2012/09/06

DOI:10.1039/C2CP42710A