Structural,electronic, and optical properties of doubly ortho‐linked quinoxaline/diphenylfluorene hybrids

The optical and electronic properties of spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(4‐t‐butylphenyl)quinoxaline) 1a , spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(4‐methoxyphenyl)quinoxaline) 1b , spiro‐fluorene‐dibenzosuberene[d](1‐(4‐(N,N‐diphenylamino)‐phenyl)‐quinoxaline) 1c , spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methylphenylamino)quinoxaline) 1d , spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methyl‐(4‐methylphenyl)amino)quinoxaline) 1e , spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methyl‐(4‐methoxyphenyl)amino)quinoxaline) 1f , 5,8‐bis‐(4‐methoxy‐phenyl)‐2,3‐diphenyl‐quinoxaline 1 , and N,N,N',N'‐tetraphenyl‐ 5h‐dibenzo[a,d]cycloheptene‐3,7‐diamine 2 were investigated theoretically in this paper. The doubly ortho‐linked quinoxaline/diphenylfluorene hybrids 1a – 1f show great potential as bipolar materials for the design of optimized organic light‐emitting diodes (OLEDs). Density functional theory (DFT) and ab initio HF were employed to study the geometric and electronic structures of these molecules in the ground state, and ab initio CIS were used to investigate the lowest singlet excited states. The radiative lifetime (τ) and the maximal absorption/emission wavelength of these molecules were calculated within time‐dependent DFT (TDDFT). The results show that the LUMO energies of the bipolar molecules 1a – 1d are all lower than those of 1 and 2 , consequently, the electron‐accepting abilities of 1a – 1d are greatly improved. The HOMO energies of 1c – 1f are all higher than those of 1 and 2 , suggesting that the hole‐creating abilities of 1c – 1f become better. Also, the results reveal that the HOMO and LUMO energies, energy gaps, IP, EA, as well as the maximal absorption/emission spectra can be tuned feasibly by changing the C5‐ and C8‐substituents in the quinoxaline backbone of these molecules. As expected, these materials show different emission spectra varying from 436.11 to 715.47 nm. Copyright © 2010 John Wiley & Sons, Ltd.     

DFT/TDDFT studies of the ancillary ligand effects on structures and photophysical properties of rhenium (I) tricarbonyl complexes with the imidazo[4,5‐f]‐1,10‐phenanthroline ligand

The seven rhenium (I) tricarbonyl complexes having a general formula fac‐[ReBr(CO)₃(R₁,R₂,R₃‐N^{^}N)] (N^{^}N = imidazo[4,5‐f]‐1,10‐phenanthroline; R₁ = ? ^tBu, R₂ = R₃ = ? H, 1 ; R₁ = ? C?CH, R₂ = R₃ = ? H, 2 ; R₁ = ? ^tBu, R₂ = ? C?CH, R₃ = ? H, 3 ; R₁ = ? ^tBu, R₂ = R₃ = ? C?CH, 4 ; R₁ = ? ^tBu, R₂ = ? CH₃, R₃ = ? H, 5 ; R₁ = ? ^tBu, R₂ = R₃ = ? CH₃, 6 ; R₁ = ? ^tBu, R₂ = ? OCH₃, R₃ = ? H, 7 ) have been investigated theoretically by density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods. The different substituted groups on N^{^}N ligand induce changes on the electronic structures and photophysical properties for these complexes. It is found that the introduction of ? C?C decreases the energy level of lowest unoccupied molecular orbital (LUMO) while the introduction of ? CH₃ or ? OCH₃ lead to increase the energy level of LUMO. The order of LUMO energy level rising is in line with the increasing of donating abilities of substituted groups; and the influence of R₂ position is greater than that of R₁ position on LUMO energy level. The lowest energy absorption bands have changes in the order of 7 < 6 < 5 < 1 < 2 < 3 < 4 . These results of electronic affinity (EA), ionization potential (IP), and reorganization energy (λ) indicate that all of these complexes can be used as electron transporting materials. Moreover, the smallest difference between λ_electron and λ_hole of 4 indicates that it is better to be used as an emitter in the organic light‐emitting diodes. © 2015 Wiley Periodicals, Inc.     

有序分子组装膜电极非理想伏安图的理论研究

在有序分子组装体系的电化学研究中,电活性物种间的相互作用直接导致其偏离理想的电化学行为,譬如出现双峰或者峰展宽的现象。从这些非理想的电化学数据中提取热力学和动力学数据显得相对困难,因而了解和评价这些非理想的电化学行为显得十分有必要。本文着重就这些非理想电化学现象的理论模型、基本公式和微观认识进行了评述。理解这些非理性电化学的影响因素,不仅加深对表面电化学体系的认识,更对现在的研究热点课题如主客体识别、分子电子器件、生物传感器等具有重要意义。     

Solvent Reorganization Energy and Electronic Coupling for Intramolecular Electron Transfer in Biphenyl-Acceptor Anion Radicals

A novel algorithm was designed and implemented to realize the numerical calculation of the solvent reorganization energy for electron transfer reactions, on the basis of nonequilibrium solvation theory and the dielectric polarizable continuum model. Applying the procedure to the well-investigated intramolecular electron transfer in biphenyl-androstane-naphthyl and biphenyl-androstane-phenanthryl systems, the numerical results of solvent reorganization energy were determined to be around 60 kJ/mol, in good agreement with experimental datKoopman's theorem was adopted for the calculation of the electron transfer coupling element, associated with the linear reaction coordinate approximation. The values for this quantity obtained are acceptable when compared with experimental results.     

Density functional theory study on organic semiconductor for field effect transistors: Symmetrical and unsymmetrical porphyrazine derivatives with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene moieties

Density functional theory (DFT) calculations were carried out to investigate the organic field effect transistor (OFET) performance of the symmetrical metal-free tetrakis (1,2,5-thiadiazole) porphyrazine (S₄)PzH₂ and tetrakis (1,4-diamyloxybenzene) (A₄)PzH₂ as well as the low-symmetry metal-free porphyrazine with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene groups in the ratio 2:2 (cis) and 1:3, that is, (cis-S₂A₂)PzH2 and (SA₃)PzH₂, (S = 1,2,5-thiadiazole ring, A = annulated 1,4-diamyloxy-benzene ring, Pz = porphyrazine) in terms of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, ionization energy (IE), electron affinity (EA), and their reorganization energy (λ) during the charge-transport process. On the basis of Marcus electron transfer theory, electronic couplings (V) and field effect transistor (FET) properties for the four compounds with known crystal structure have been calculated. The electron transfer mobility (μ₋) is revealed to be 0.056 cm²·V⁻¹·s⁻¹ for (S₄)PzH₂. The hole transfer mobility (μ₊) is 0.075, 0.098, and 8.20 cm²·V⁻¹·s⁻¹ for (cis-S₂A₂)PzH₂, (SA₃)PzH₂, and (A₄)PzH₂, respectively. The present work represents the theoretical effort towards understanding the OFET properties of symmetrical and unsymmetrical porphyrazine derivatives with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene. Supported by the National Natural Science Foundation of China (Grant No. 50673051) and Beijing Municipal Commission of Edueation     

Applying strong external electric field to thiophene‐based oligomers: A promising approach to upgrade semiconducting performance

A key parameter dictating the rate of charge transfer (CT) is reorganization energy (λ ), an energy associated with geometry changes during hole/electron transfer. We show that “ironing” the inter‐ring dihedral angles of oligothiophenes via proper substitutions or insertions (e.g., ‐OR, ‐F or ‐C≡C‐), decreases the λ and thus promotes CT according to Marcus equation. Our results demonstrate, to attain a smaller λ , extending oligomer length is only significant if the flattened backbone structure is realized. Of great interest is that external electric fields, which are ubiquitous in electronic devices yet commonly overlooked in the computation of λ , can have a significantly greater impact than conventional substitutions. It is important to emphasize, the responses of λ to external fields is system‐dependent. Compared to fused‐ring conjugated systems, single‐bond connected thiophenes are more sensitive to external fields. F_x lowers the λ (552 meV) of quaterthiophene by almost 80% at the intensity of 1 V/Å, down to a value (125 meV) which is even lower than that of pentacene (154 meV) and rubrene (219 meV) at the same level of theory. © 2016 Wiley Periodicals, Inc.     

"嫁接型"校园改扩建工程的继承和创新--台州市路桥中学教学实验楼设计

结合路桥中学教学实验楼扩建工程的设计实践,分析了改扩建工程的特点,提出了“嫁接型”校园的新概念;阐述了如何通过对原有校园环境、空间布局、建筑形态等的分析和整合,寻求设计的切入点;并以此来探讨“嫁接型”校园改扩建工程的设计方法以及此类校园改扩建工程的继承和创新问题.