Theoretical investigations on electronic structures and photophysical properties of novel bridged triphenylamine derivatives

It has been proved that triphenylamine (TPA) derivatives can be excellent candidates for hole‐transporting materials in organic light‐emitting diodes (OLEDs). To improve on the thermal and morphological stability, a fully diarymethylene‐bridged TPA derivative (FATPA) which has been proven to enhance electroluminescent (EL) efficiency was synthesized. On the basis of FATPA, two series of novel bridged TPA derivatives have been designed by using diarylmethylene (Series A) or dimethyfluorene (Series B) as the linkage between the ortho‐positions of the phenyl rings in this work (see Fig. 1 ). To reveal the relationships between electronic structures and photophysical properties of these novel functional materials, an in‐depth theoretical investigation was elaborated via quantum chemical calculations using the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods. In addition, the feasibility of using these bridged TPA derivatives as host in the device of ITO/MoO₃/NPB/mCP/host:Ir(ppy)₃/TAZ/LiF/Al was also evaluated, which including the discussion to their energy levels match with adjacent layers and energy transfer from host to guest. These calculated results show that photophysical properties can be easily tuned by the introduction of various substituent groups into the bridged TPA derivatives, such as the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), the energies difference between the HOMOs and LUMOs (Δ_H‐L), the lowest singlet (E_S) and triplet (E_T) excitation energies, ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ) and the absorption and emission spectra, indicating that these bridged TPA derivatives have great potential applications for OLEDs. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

洛汾碱衍生物的电子结构及光谱性质的理论研究

采用密度泛函理论(DFT)的B3LYP/6-31G*方法,对4种洛汾碱类化合物的几何构型进行了优化,在此基础上计算分子的电子结构,并结合有限场FF方法研究了二阶非线性光学(NLO)性质.用含时密度泛函理论(TD-DFT)对上述化合物分子进行吸收光谱的研究.研究表明在4,5-二-苯基-2-对甲酰苯基咪唑生色团中4,5苯环上引入硝基和3位N原子引入苄基改变分子的共轭平面,使二阶非线性极化率总有效值(βtot)减小,吸收峰总体蓝移.同时还发现,在CH2Cl2溶剂中a和c分子的λmax主要来源于HOMO→LUMO的π一π*跃迁,b和d分子的λmax主要来源于HOMO→LUMO+2的π→π*跃迁.     

Theoretical study on photophysical properties of bis-dipolar diphenylamino-endcapped oligoarylfluorenes as light-emitting materials

Bis-dipolar emissive oligoarylfluorenes, OF(2)Ar-NPhs(2), bearing an electron affinitive core, 9,9-dibutylfluorene, as conjugated bridges and diphenylamino as endcaps, show great potential for application in organic light-emitting diodes. The various electron affinitive central aryl cores that include thiophene S,S'-dioxide, dibenzothiophene S,S'-dioxide, 2,1,3-benzothiadiazole, 4,7-dithien-2-yl-2,1,3-benzothiazole, dibenzothiophene, and dibenzofuran produce a remarkable influence on their optical and electronic properties. In this contribution, we apply quantum-chemical techniques to investigate a series of bis-dipolar diphenylamino-endcapped oligoaryfluorenes, OF(2)Ar-NPhs(2). The geometric and electronic structures in the ground state are studied using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states are optimized with ab initio CIS. The maximal absorption and emission wavelengths are investigated by employing time-dependent density functional theory (TDDFT). As a result, HOMOs, LUMOs, energy gaps, ionization potentials, electron affinities, and reorganization energies are affected by varying the electron affinitive cores in OF(2)Ar-NPhs(2). The absorption and emission spectra of this series of bis-dipolar oligoarylfluorenes also exhibit red shifts to some extent due to the electron-withdrawing property and the conjugated length of the electron affinitive cores. Remarkably, their calculated emission spectra can cover the full UV-vis spectrum (from 412 to 732 nm). Also, the Stokes shifes are unexpectedly large, ranging from 34 to 234 nm, resulting from a more planar conformation of the excited state between the two adjacent units in the oligoarylfluorenes. All the calculated results show that the oligoarylfluorenes can be used as hole and electron transport/injection materials in organic light-emitting diodes.     

Theoretical investigations on geometrical and electronic structures of silver clusters

Geometrical structures and ground and excited states of silver clusters are theoretically investigated using long-range corrected (LC) density functional theory (DFT) calculations. The discrepancy between HOMO-LUMO gaps and the vertical ionization potential minus vertical electron affinity values, which should be the same values, is explored to reveal the significance of long-range exchange effects on the electronic states of metal clusters. The difference between HOMO-LUMO gaps and HOMO-LUMO excitation energies, which is called “exciton binding energy,” is also tested. As a result, it is found that the long-range exchange effects are requisite in DFT calculations to quantitatively investigate the ground and excited states of metal clusters. © 2018 Wiley Periodicals, Inc.     

Synthesis and device properties of carbazole/benzimidazole-based host materials

We report two bipolar host materials bearing hole-transport benzofurocarbazole/indenocarbazole cores and an electron-transport benzimidazole moiety for red phosphorescence organic light emitting devices (PhOLEDs). The two novel host materials exhibited excellent physical properties with high thermal stabilities, appropriate HOMO-LUMO energy levels and balanced charge transport. Both of them were applied to fabricate red PhOLEDs as promising host materials, and 7,7-dimethyl-5-(4′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′-biphenyl]-4-yl)-5,7-dihydroindeno[2,1-b]carbazole (ICBI) based device demonstrated outstanding electroluminescence performance with the maximum current efficiency, power efficiency and external quantum efficiency of 33.0 cd/A, 13.9 lm/W and 18.9%, respectively.     

苯并噻二嗪衍生物电子结构和非线性光学性质的研究

运用量子化学PM3方法，对苯并噻二嗪几种衍生物的几何构型、电子结构和前线分子轨道成分进行了分析，研究了电荷分布规律。同时，基于体系中电子转移的特点，利用有限场FF方法探讨了其非线性光学性质的变化。结果表明，苯并噻二嗪分子具有较好的二阶非线性光学性质，并可能成为一类良好的光学材料。     

Synthesis and photophysical properties of tetrafluorophenyl-modified carbazole oligomers

A series of tetrafluorophenyl-modified oligo(3,6-carbazole ethynylene)s (CfCzCf, CfCz2Cf, CfCz3Cf, (CfCz)2Cf, and Cf2CzCf2) were synthesized by a Pd/Cu-catalyzed Sonogashira coupling reaction and fully characterized. Their photophysical and electronic properties as well as their thermal stabilities were investigated. It is noteworthy that these tetrafluorophenyl modified compounds showed relative thermal stabilities and low-lying HOMO levels ranging from −5.54 to −5.60 eV, which might be the promising candidates for hole-transporting materials in OLEDs.     

Theoretical investigations on the geometric and electronic structures of phenylene-acetylene macrocycles.

The geometric and electronic structures of a series of conjugated macrocycles (phenylene-acetylene macrocycles, PAMs) have been studied theoretically with ab initio and semiempirical molecular orbital methods. The ab initio calculations at the HF/6-31G* level demonstrate that the model molecules may have a planar conformation. Bigger macrocycles, for example, 7PAM, 8PAM, and 9PAM, result in several energy minima. The boatlike conformation is the most energetically favored form. Based on the conformational analysis, a novel method for analyzing the ring-strain energy was proposed and used. In view of their potential applications as electronic materials, the electronic structures of a series of PAMs are also investigated. The LUMO-HOMO gaps of the planar PAMs show an odd-even difference behavior. In addition, the HOMOs of the planar species 3PAM, 5PAM, 7PAM, and 9PAM are doubly degenerated.     

苯并噻二嗪吸电子基取代衍生物电子性质的理论研究

运用量子化学半经验方法对1，2，4-苯并噻二嗪-1，1二氧类化合物的8种取代衍生物进行了量子化学计算，从体系能量、几何构型、电子结构、前线分子轨道等几方面分析了吸电子基-CN，-NO2等取代后体系的电子性质变化规律．结果表明：随着取代基吸电子能力的增强，体系的活性增强，可为药物合成提供一定的理论指导．     

Theoretical studies on molecular and structures of mono- and binuclear chromium carbazole derivatives for optoelectronics

Studies on the molecular geometries, electronic properties and second-order nonlinearities of a series of mono- and binuclear chromium carbazole complexes: (N-vinylcarbazole)Cr(CO)(3) (M1), (N-vinylcarbazole)Cr(CO)(2)PPh(3) (M2), (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(3) (B1), and (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(2)PPh(3) (B2) were carried out, using the density functional theory (DFT) at the B3LYP//LanL2DZ/6-31G(d) level. The experimental singlet metal-to-ligand charge transfer ((1)MLCT) spectra of these complexes can also be well simulated and discussed by the time-dependent DFT (TDDFT) at the B3LYP//LanL2DZ/6-311+G(d) level associated with the polarizable continuum model (PCM). The computational results show that an unusual characteristic of chromium carbazole structures is explained in terms of interaction between frontier molecular orbitals of the metal and its ligands. The highest occupied molecular orbitals (HOMOs) of these complexes are composed of a set of distorted degenerated Cr 3d orbitals, whereas the lowest unoccupied molecular orbitals (LUMOs) are predominantly the N-vinylcarbazole ligand π* orbitals. The HOMO-LUMO energy gaps decrease in the order NVC > M1 > B1 > M2 > B2. The considerable coupling between the carbazole and (CO)(3) in M1 creates an asymmetric environment about the chromium atom, leading to modest second-order responses. The PPh(3) ligand is acting as a donor which increases the donating strength of the d(π) orbitals in chromium carbazole species, resulting in the large electronic asymmetry in M2. As for the binuclear chromium carbazole chromophores, a wide-range (1)MLCT band and large oscillator strength are found, allowing for the electronic interactions between two metal centers which can be modified by altering the ligand bound to the metals to induce peculiar asymmetry. Essentially, Cr(CO)(3) acceptor and Cr(CO)(2)PPh(3) donor units in B2 make significant contribution to the charge-transfer process or NLO responses via conventional push-pull chromophoric architecture.     

酞菁及其不对称取代物的电子结构和非线性光学特 性的理论研究

利用AM1方法计算多种酞菁不对称取代物的电子结构与非线性光学特性,并探讨它们之间的关系。结果表明偶极矩μ,能级差△E~D~A,电荷转移△Q~D~A与二阶非线性光学系数β之间都存在一定的规律性,其中μ与β和△E~D~A与β之间的关系较为明显,并有相似趋势。     

Theoretical and experimental investigations of complexation with BF3.Et2O effects on electronic structures,energies and photophysical properties of Anil and tetraphenyl (hydroxyl) imidazol

The novel compounds (E)‐2‐(((4‐hydroxyphenyl)imino)methyl)phenol, Tetraphenyl (hydroxyl) imidazole and their corresponding Boron difluoride complexes were synthesized and characterized by spectroscopic techniques. Density functional theory calculations at B3LYP‐D3/6–311++G (d, p) level of theory were performed for the geometric parameters. The MEP surface studies were used to understand the behavior of molecules in terms of charge transfer and to determine how these molecules interact. We used the GIAO and the B3LYP‐D3 with a 6–311++ G (d, p) basis set to simulate the (¹H‐NMR and ¹⁹F‐NMR) and the IR spectra, respectively. The corresponding calculated results are in good agreement with the experimental data. The stability of the molecule arising from hyperconjugation interaction and charge delocalization were analyzed using NBO analysis. FMOs revealed the occurrence of charge transfer within the molecule. The complexation using BF₃.Et₂O was also found to have remarkable effects on the electrochemical properties of the studied molecules, where (b) and (d) present lower chemical stability, higher reactivity and higher polarizability than (a) and (c), respectively. Moreover, the energy gap of (a) and (c) decreased after complexation using BF₃.Et₂O, indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. These values are the factors explaining the possible charge transfer interaction within the molecule. The absorption and emission spectra of the model compound were also simulated and compared to experimental observations in the DMF solvent. The results of DFT calculations supported the structural and spectroscopic data and confirmed the structure modification of frontier molecular orbitals for BF₂ complexes as well as tunable potentials and energy levels.     

Synthesis, crystal structures, and photophysical properties of triphenylamine-based multicyano derivatives

A new series of intramolecular charge transfer (ICT) molecules were synthesized by attaching various strong electron-withdrawing groups to a triphenylamine backbone. Relationships between chemical structures and optoelectronic properties of these compounds were investigated with X-ray diffraction, cyclic voltammetry, absorption spectroscopy, and density functional theory calculations. It is shown that the compounds exhibit intensive ICT interactions leading to substantial extension of their absorption spectral response, which may be potentially used for efficient solar cells.     

基于喹喔啉和吡啶并吡嗪及咔唑和二苯胺衍生物电子给体-受体结构荧光材料的合成和光电性能

通过α-二酮与邻苯二胺、吡啶二胺缩合反应,构建了喹喔啉和吡啶并吡嗪衍生物作为电子受体,分别以二苯胺、咔唑衍生物为电子给体,合成了 4个具有电子给体-电子受体结构的氮杂环荧光材料 F1~F4。通过低温荧光/磷光光谱、荧光寿命测试,结合密度泛函理论计算可知,F1~F4均为荧光小分子。室温荧光光谱结果表明,利用电子给体和受体的电子效应不同可以调控材料的发光颜色,其中三苯胺相对于苯基咔唑的供电子能力更强,表现为F1比F2、F3比F4红移现象更加明显;而吡啶并吡嗪具有多氮的缺电子结构,与喹喔啉相比共轭程度增加,导致 F3 比 F1、F4 比 F2 发生的斯托克斯位移数值增大。总之,F1~F4的甲苯溶液最大荧光光谱发射峰位于 529、464、568和 507 nm,荧光寿命分别为 12.21、2.61、9.76和 6.03 ns,荧光量子效率最高可达98.2%,具有良好的发光性能。将F1~F4发光材料掺杂在主体材料中制备了有机电致发光二极管DF1~DF4。所得器件DF1和DF3性能更好,最大电流效率分别为13.38和11.98 cd·A^-1,且最大外量子效率分别达到4.8%和4.5%。     

基于喹喔啉和吡啶并吡嗪及咔唑和二苯胺衍生物电子给体-受体结构荧光材料的合成和光电性能

通过α-二酮与邻苯二胺、吡啶二胺缩合反应,构建了喹喔啉和吡啶并吡嗪衍生物作为电子受体,分别以二苯胺、咔唑衍生物为电子给体,合成了4个具有电子给体-电子受体结构的氮杂环荧光材料F1~F4。通过低温荧光/磷光光谱、荧光寿命测试,结合密度泛函理论计算可知,F1~F4均为荧光小分子。室温荧光光谱结果表明,利用电子给体和受体的电子效应不同可以调控材料的发光颜色,其中三苯胺相对于苯基咔唑的供电子能力更强,表现为F1比F2、F3比F4红移现象更加明显;而吡啶并吡嗪具有多氮的缺电子结构,与喹喔啉相比共轭程度增加,导致F3比F1、F4比F2发生的斯托克斯位移数值增大。总之,F1~F4的甲苯溶液最大荧光光谱发射峰位于529、464、568和507 nm,荧光寿命分别为12.21、2.61、9.76和6.03 ns,荧光量子效率最高可达98.2%,具有良好的发光性能。将F1~F4发光材料掺杂在主体材料中制备了有机电致发光二极管DF1~DF4。所得器件DF1和DF3性能更好,最大电流效率分别为13.38和11.98 cd·A^-1,且最大外量子效率分别达到4.8%和4.5%。     

A boron-containing carbazole dimer: synthesis, photophysical properties and sensing properties

A novel boron-containing π-conjugated compound has been synthesized by the introduction of electron-acceptors (dimesitylboron groups) at the 3,3'-positions of a carbazole dimer (electron-donor). The compound possesses excellent electrochemical properties and high fluorescence quantum yields. In addition, is a sensitive fluorescence sensor with remarkable colour changes and the results could be confirmed through theoretical calculations of the compounds and [(n)Bu(4)N](+)(2)[·(F)(2)](2-). Our studies indicate that could be used as an excellent optoelectronic material in OLED devices and a ratiometric fluorescent chemosensor.     

Theoretical studies on the electronic and optical properties of two new alternating fluorene/carbazole copolymers

Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (Delta(H-L)), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (E(g)s) and the maximal absorption wavelength lambda(abs) of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as Delta(H-L), E(g), IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)(n) series.     

Theoretical study of electronic properties of organic photovoltaic materials

It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C(60), present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p-phenylenevinylene (n-PPV, n = 3-8 units) and C(60)-OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorption and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent-density functional theory (TD-DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n-PPV and fullerene-OPV hybrids were obtained using PBE1PBE/6-31G and ONIOM two-layered version, respectively. All calculations were done with Gaussian 03W program package.     

Optical and photophysical properties of indolocarbazole derivatives

We present a study of the optical and photophysical properties of five ladder indolo[3,2-b]carbazoles, namely, M1, M2, M3, M4, and M5. The ground-state optimized structures were obtained by B3LYP/6-31G* density functional theory (DFT) calculations, whereas the optimization (relaxation) of the first singlet excited electronic state (S1) was performed using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S1 state does not cause important changes in the geometrical parameters of the compounds, as corroborated by the small Stokes shifts. The excitation and emission energies have been obtained by employing the time-dependent density functional theory (TDDFT). For all the compounds, excitation to the S1 state is weakly allowed, whereas the S2 <-- S0 electronic transition of each oligomer possesses a much larger oscillator strength. The absorption and fluorescence spectra of the compounds have been recorded in chloroform. A reasonable agreement is obtained between TDDFT vertical transition energies and the (0,0) absorption and fluorescence bands. On one hand, the pattern of the aliphatic side chains does not affect the absorption and fluorescence maxima of the compounds. On the other hand, the replacement of aliphatic chains by phenyl or thiophene rings induces hypsochromic shifts in the absorption and fluorescence spectra. Finally, the fluorescence quantum yield and lifetime of the compounds in chloroform have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S1 state have been determined.