Theoretical study on optical and electronic properties of bis-dipolar 1,8-naphthalimide derivatives

A series of donor–π–acceptor type of 1,8-naphthalimide derivatives with ethylene as π-conjugated bridges have been designed to explore their optical and electronic properties as luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbital analysis turned out that the vertical electronic transitions of absorption and emission are characteristic as intramolecular charge transfer. The calculations showed that their optical and electronic behaviours are clearly affected by the aromatic substitute groups, but not significantly to the stability of molecules. The calculated results suggest that all the selected candidates are promising as luminescent materials for OLEDs.     

Theoretical study on alkyne-linked carbazole polymers for blue-light multifunctional materials

This paper studied poly[(3,6-di-tert-butyl-N-hexadecyl-1,8-carbazolylene) butadiynylene] (P1), butadiynylene-linked poly (3,6-carbazole) (P2) and butadiynylene-linked poly (2,7-carbazole) (P3) through the theoretical measurements with Gaussian 03 program package. To investigate the relationship between structures and properties of these multifunctional electroluminescent materials, their geometrical structures of ground and excited-states were optimized by B3LYP/6-31G (d) and CIS/6-31G (d) methods, respectively. The lowest excitation energies (E_g's), and the maximum absorption and emission wavelengths of these polymers were calculated by time-dependent density functional theory methods (TD-DFT). The important parameters for luminescent materials were also predicated including the ionization potentials (I_p's) and electron affinities (E_a's). The calculated results show that the highest-occupied molecular orbital (HOMO) energies lift about 0.27-0.49 eV compared to N,N′-bis(naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), suggesting the significant improved hole-accepting and transporting abilities. In addition, substitution of alkyne for carbazole resulted in a narrow band gap and a red shift of both the absorption and emission peaks. Through above calculations, it is evidenced that these polymers can be considered as candidates for excellent OLEDs with good hole-creating abilities and high blue-light emission.     

Theoretical studies on nitrogen‐rich furoxan‐based heterocyclic derivatives

The density functional theory method was used to study the heats of formation (HOFs), energetic properties, electronic structure of a series of 4,4″‐dinitro(3,3′:4′,3′′)tris([1,2,5]oxadiazole)‐2′‐oxide (3,4‐bis[4′‐nitrofurazan‐3′‐yl]furoxan) derivatives. The results show that the substitution of the nitro group is very useful for improving their HOFs and detonation performances. The HOFs of the title compounds are all positive and larger than those of 1,3,5‐trinitro‐1,3,5‐triazinane and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane. The analysis of oxygen balance shows that the studied compounds need the oxygen in the explosive. Compound A1 has larger detonation velocity and detonation pressure than those of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane and can be regarded as a potential candidate for high‐energy compounds because of the moderate heat of detonation, high density, and high N. In addition, the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital of the studied compounds are further investigated.     

新型稀磁半导体Mn掺杂LiZnAs的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法, 对纯LiZnAs, Mn掺杂的LiZnAs, Li过量和不足下Mn掺杂的LiZnAs体系进行几何结构优化, 计算并对比分析了体系的电子结构、半金属性、光学性质及形成能.结果表明新型稀磁半导体Li (Zn_0.875Mn_0.125) As, Li_1.1 (Zn_0.875Mn_0.125) As和Li_0.9 (Zn_0.875Mn_0.125) As均表现为100%自旋注入, 材料均具有半金属性, Li过量和不足下体系的半金属性明显增强. Li过量可以提高体系的居里温度, 改善材料的导电性, 使体系的形成能降低. 说明LiZnAs半导体可以实现自旋和电荷注入机理的分离, 磁性和电性可以分别通过Mn的掺入和Li的含量进行调控. 进一步对比分析光学性质发现, 低能区的介电函数虚部和复折射率函数明显受到Li的化学计量数的影响. 关键词： Mn掺杂LiZnAs 电子结构 光学性质 第一性原理     

BaZrO3和CaZrO3能带和光学性质的第一性原理研究

采用基于密度泛函理论基础上的CASTEP软件包,计算了BaZrO3和CaZrO3的能带以及光学性质.计算得到BaZrO3直接带隙和间接带隙分别为3.49 eV和3.23eV,CaZrO3直接带隙和间接带隙分别为3.73 eV和3.38 eV.对这两种材料的介电函数、吸收系数、反射系数、折射系数、湮灭系数和能量损失系数等光学系数进行了计算,并基于电子能带对光学性质进行了解释.得出,光学特性的异同是由于其内部微观结构上的异同所引起的.     

Electronic structures and optical properties of TiO₂:Improved density-functional-theory investigation

TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha’s modified Becke-Johnson(TB-mBJ) exchange potential(plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation(LDA) and generalized gradient approximation(GGA),in contrast with substantially overestimated values from many-body perturbation(GW) calculations.As for optical dielectric functions(both real and imaginary parts),refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.     

Theoretical studies on 2‐(5‐amino‐3‐nitro‐1,2,4‐triazolyl)‐3,5‐dinitropyridine (PRAN) and its derivatives

In this work, a set of derivatives of 2‐(5‐amino‐3‐nitro‐1,2,4‐triazolyl)‐3,5‐dinitropyridine (PRAN) with different energetic substituents (?N₃, –NO₂, –NH₂, –NF₂) have been studied at the Becke, three‐parameter, Lee–Yang–Parr/aug‐cc‐pvdz, Becke, three‐parameter, Lee–Yang–Parr/6‐31G(d), Becke, three‐parameter, Perdew 86/6‐31G(d), and Becke three‐parameter, Perdew–Wang 91/6‐31G(d,p) levels of density functional theory. The gas‐phase heats of formation were predicted with isodesmic reactions and the condensed‐phase HOFs were estimated with the Politzer approach. The effects of different functionals and basis sets were analyzed. –N₃ and –NO₂ greatly increase while –NH₂ and –NF₂ slightly decrease heats of formation. An analysis of the bond dissociation energies and impact sensitivity shows that all compounds have good stability. The crystal densities (1.82–2.00 g/cm³) computed from molecular packing calculations are big for all compounds and that of the –NF₂ derivative is the largest. All derivatives have higher detonation velocity and detonation pressure than PRAN. Compounds 3 and 4 (R = NO₂ and NF₂) have better performance than hexahydro‐1,3,5‐trinitro‐1,3,5‐trizine and the performance of 4 is quite close to that of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane, they are promising candidates of high energy compounds and worth further investigations. Copyright © 2012 John Wiley & Sons, Ltd.     

Bacteria‐based branched structures for bionanophotonics

Branched photonic structures have served as paramount important components for nanophotonic integration and circuitry. However, these structures are generally constructed with photonic and plasmonic nanowires, which are nonbiomaterials and often need to be specially engineered to interface with cells and biological system. For bionanophotonics, photonic components assembled with self‐adaptive biomaterials are highly desirable to be directly interfaced with the dynamic biological system. In this work, branched structures for bionanophotonics assembled with natural living biomaterials, i.e., nanorod‐shaped Escherichia coli bacteria are reported. The E. coli cells were orderly trapped using a specially desired tapered optical fiber, forming structures with different branches and lengths. Light‐propagation performances along these branched structures were investigated, and the robustness property of the structures were demonstrated. The results show that the bacteria‐based branched structures provide different promising self‐sustainable and evolvable components, such as multidirectional waveguides and beam splitters, for bionanophotonics by connecting the biological and optical worlds with a seamless interface.

     

太赫兹波发射晶体的亚波长微棱锥增透结构的设计与实验研究

光学整流方法产生太赫兹(THz)辐射常用的非线性发射晶体在THz波段都具有较高的折射率, 使得很大一部分THz波由于晶体表面的菲涅尔反射而无法有效耦合输出. 本文报道了GaP晶体THz波发射器输出表面上亚波长微棱锥增透结构的设计和实验研究. 利用有效介质模型在理论上验证了亚波长光栅结构的增透效果, 并进一步设计了适用于不同频段的增透结构的参数. 实验中, 通过微机械加工手段在GaP晶体输出端面刻划了多种亚波长微棱锥结构, 验证了其增透效果及参数对增透频带的关系. 理论与实验的符合证明该设计思想也可用于其他THz波发射晶体. 关键词： THz波 光学整流 亚波长微棱锥增透结构 微加工     

Manipulating charge‐transfer character and tuning emission color with electron‐withdrawing main‐group moieties in iridium‐based electrophosphors: a theoretical investigation

A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2‐phenylpyridine) with various main group moieties in [Ir(ppy‐X)₂(acac)] (X = POPh₂, SO₂Ph, GePh₃, OPh, OPh(CF₃)₃, SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time‐dependent density functional theory (TD‐DFT) and Hartree–Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD‐DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground‐ and excited‐state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light‐emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron‐injection and electron‐transporting features. Copyright © 2012 John Wiley & Sons, Ltd.     

m-BiVO_4与t-BiVO_4的电子结构和光学性质的第一性原理研究

采用第一性原理的密度泛函理论赝势平面波方法,计算了单斜m-BiVO_4与四方t-BiVO_4的电子结构和光学性质.计算结果表明:m-BiVO_4为间接带隙半导体,禁带宽度为2.171 e V,t-BiVO_4为直接带隙半导体,禁带宽度为2.644 e V;m-BiVO_4与t-BiVO_4均可吸收紫外光及可见光,m-BiVO_4还可以吸收部分红外光.     

W掺杂ZnO电子结构与光学性质第一性原理计算

采用了基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算本征ZnO和不同W掺杂浓度下W:ZnO体系的电子结构和光学性质.计算结果表明:W掺杂可以提高ZnO的载流子浓度,从而改善ZnO的导电性.掺杂后,吸收光谱发生红移现象,且光学性质变化集中在低能量区,而高能量区的光学性质没有太大变化,计算结果与相关实验结果相符合.最后,结合电子结构定性分析了光学性质的变化.     

(Cu,N)共掺杂TiO2/MoS2异质结的电子和光学性能:杂化泛函HSE06

在密度泛函理论的基础上,系统地研究了Cu/N（共）掺杂的TiO₂/MoS₂异质结体系的几何结构、电子结构和光学性质.计算发现,TiO₂/MoS₂异质结的带隙相比于纯的TiO₂（101）表面明显变小,Cu/N（共）掺杂TiO₂/MoS₂异质结体系的禁带宽度也明显地减小,这导致光子激发能量的降低和光吸收能力的提高.通过计算Cu/N（共）掺杂TiO₂/MoS₂的差分电荷密度,发现光生电子与空穴积累在掺杂后的TiO₂（101）表面和单层MoS₂之间,这表明掺杂杂质体系可以有效地抑制光生电子-空穴对的复合.此外,我们计算了在不同压力下TiO₂/MoS₂异质结的几何、电子和光学性质,发现适当增加压力可以有效提高异质结的光吸收性能.本文结果表明,Cu/N（共）掺杂TiO₂/MoS₂异质结和对TiO₂/MoS₂异质结加压都能有效地提高材料的光学性能.     

不同浓度下V掺杂Mg2Si的第一性原理研究

本文用基于密度泛函理论的超软赝势平面波方法,分别计算了四种V掺杂模型Mg_2-xV_xSi(x=0,0.25,0.5,0.75)的电子结构和光学性质,并对其能带图、态密度图和光学性质进行了分析.结果表明,V掺杂之后会使Mg₂Si由其原本的半导体性变为半金属性,在费米能级处出现了杂质能级,态密度图也显示V元素的3d轨道的贡献在费米能级附近占据主导地位,Mg₂Si的光学性质随着V元素的掺入也发生了改变.该文为Mg₂Si材料在电子器件和光学器件方面的应用提供了理论依据.     

Organic‐inorganic hybrids based on phenanthrene‐functionalized gold nanoparticles for OLEDs

The electroluminescence intensity of the phenanthrene‐functionalized gold nanoparticles, PMPT‐Au nanoparticles/CPB: Ir(PIA)₂ (acac) film, was increased by 4.9 times compared with control device, CPB: Ir(PIA)₂ (acac) due to coupling between the excitons of emissive layer and localized surface plasmonic resonance of PMPT‐Au NPs. The maximum luminous efficiencies of devices II to IV with PMPT‐Au NPs were 39.2 cd A^?1 (11.8 V), 40.1 cd A^?1 (10.5 V), and 43.1 cd A^?1 (9.0 V), respectively. The increment of current efficiency with PMPT‐Au NP coated devices was strongly related to the energy transfer between the radiated light generated from CBP: Ir(PIA)₂ (acac) emissive layer and localized surface plasmonic resonance excited by PMPT‐Au NP layer.     

Theoretical investigation of electronic properties and redox properties for purely inorganic and aryloxide substituted Ti-containing POM derivatives

DFT calculations have been performed to investigate the redox properties and electron transition for a series of purely inorganic and aryloxide substituted Ti-containing polyoxometalate (POM) derivatives. The modification of organic conjugated groups dramatically alters the HOMO population and decreases the energy gap. It is evident from redox analysis that Ti atoms are preferred redox centres in organic–inorganic hybrid Ti-containing POMs, and the incorporation of π-conjugated groups evokes anodic shift for reduction potential. In contrast with mono-TiW₅O₁₈ derivatives, bi-TiW₅O₁₈ derivatives exhibit narrower energy gaps and more active redox properties. It is noteworthy that the attachment of π-conjugated groups induces the low-energy electron transition to be a significant bathochromic-shift, and it has been dramatically red-shifted by 296 nm in compound 1c in contrast with that in compound 1a. When the two TiW₅O₁₈ units are covalently linked as terminals to construct bi-TiW₅O₁₈ derivatives, the low-energy electron transition presents further bathochromical shift compared with corresponding mono-TiW₅O₁₈ derivatives. In addition, the crucial charge transfer for the hybrid Ti-containing POMs are generated from π-conjugated donor to d-Ti orbital with part of p–O_c orbitals. The incorporation of the organic substituents results in attached POMs by covalent linkage to the catalyst supports, which consequently enhances the ability of catalysis.     

Theoretical insights on a series of difluoramino group–based energetic molecules

A series of difluoramino group–based energetic molecules was designed and the relative properties were investigated by density functional theory. The results show that all the designed molecules have high positive heat of formation which ranges from 479.48 to 724.02 kJ/mol, detonation velocity ranges from 8.01 to 11.26 km/s, detonation pressure ranges from 28.03 to 63.46 GPa, and impact sensitivity ranges from 18.2 to 54.5 cm. Then, compounds D2, D3, D5, E4, E5, E6, and F2 were selected as the potential high energy density materials based on detonation properties and sensitivities. Natural bond orbital charges, electronic density, frontier molecular orbital, electrostatic potential on the surface, and thermal dynamic parameters of the screened molecules (compounds D2, D3, D5, E4, E5, E6, and F2) were also predicted at B3LYP/6‐31G(d,p) level to give a better understanding on the chemical and physical properties of them.     

Theoretical study of energetic trinitromethyl‐substituted tetrazole and tetrazine derivatives

Density functional theory method was used to study the heats of formation, energetic properties, and thermal stability for a series of trinitromethyl‐substituted tetrazole and tetrazine derivatives with different substituents. It is found that the group ―NO₂, ―NHNO₂, or ―NF₂ play a very important role in increasing the heats of formation of the derivatives. The calculated detonation velocities and pressures indicate that the group ―CF₂NF₂, ―NHNO₂, ―1H‐tetrazolyl, ―2H‐tetrazolyl, or ―1,2,4,5‐tetrazinyl is an effective structural unit for enhancing their detonation performance. An analysis of the bond dissociation energies for several relatively weak bonds indicates that incorporating the group ―NHNO₂ and ―NH₂ into parent ring decreases their thermal stability. Considering the detonation performance and thermal stability, 37 compounds may be considered as the potential high‐energy compounds. Their oxygen balances are close to zero. These results provide basic information for the molecular design of novel high‐energy compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

Time‐dependent density functional theory study on the excited‐state hydrogen bonding strengthening of photoexcited 4‐amino‐1,8‐naphthalimide in hydrogen‐donating solvents

The time‐dependent density functional theory (TDDFT) method was performed to investigate the excited‐state hydrogen bonding dynamics of 4‐amino‐1,8‐naphthalimide (4ANI) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground‐state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated 4ANi and hydrogen‐bonded 4ANi‐(MeOH)_1,4 complexes were calculated by the DFT and TDDFT methods, respectively. We demonstrated that the intermolecular hydrogen bond C═O···H–O and N–H···O–H in the hydrogen‐bonded 4ANi‐(MeOH)_1,4 is strengthened in the electronically excited state, because the electronic excitation energies of the hydrogen‐bonded complex are correspondingly decreased compared with that of the isolated 4ANi. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electronically excited state of fluorescent dye in hydrogen‐donating solvents exists in many other systems in solution. Copyright © 2013 John Wiley & Sons, Ltd.