Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (E_g) between the E_HOMO and E_LUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.     

The electronic absorption spectra of some acyl azides molecular orbital treatment

The electronic absorption spectra of benzoyl azide and its derivatives: p-methyl, p-methoxy, p-chloro and p-nitrobenzoyl azide were investigated in different solvents. The observed spectra differ basically from the electronic spectra of aryl azides or alkyl azides. Four intense pi-pi* transitions were observed in the accessible UV region of the spectrum of each of the studied compounds. The contribution of charge transfer configurations to the observed transitions is rather weak. Shift of band maximum with solvent polarity is minute. On the other hand, band intensity is highly dependent on the solvent used. The observed transitions are delocalized rather than localized ones as in the case with aryl and alkyl azides. The attachment of the CO group to the azide group in acyl azides has a significant effect on the electronic structure of the molecule. The arrangements as well as energies of the molecular orbitals are different in acyl azides from those in aryl azides. The first electronic transition in phenyl azide is at 276 nm, whereas that of bezoyle azide is at 251 nm. Ab initio molecular orbital calculations using both RHF/6-311G* and B3LYP/6-31+G* levels were carried out on the ground states of the studied compounds. The wave functions of the excited states were calculated using the CIS and the AM1-CI procedures.     

共轭CN与非共轭CF3吸电子取代基对PPV类衍生物分子结构及光电性质的影响

运用密度泛函DFT B3LYP／6-31G(d)方法对CN和CF3吸电子基团取代的PPV类衍生物的三聚体进行了几何构型优化,并采用含时密度泛函TD-DFT、B3LYP／6-31G(d)方法计算了其相应化合物的紫外吸收光谱．通过对CN和CF3取代的PPV类衍生物的分子几何结构、前线分子轨道能级、电子云分布规律的分析,从理论上解释了共轭CN与非共轭CF3吸电子取代基对其光谱性质影响的差异：前者使相应PPV类衍生物的吸收光谱发生红移,后者则发生蓝移．计算结果还表明用TD-DFT方法计算该体系的紫外吸收光谱值与实验数据吻合得很好;另外引入CN和CF3基团之后,使其相应的PPV衍生物的LUMO能级降低,电子亲合势增加,都是很好的电子传输材料．     

Substituent Effect on the π Linkers in Triphenylamine Dyes for Sensitized Solar Cells: A DFT/TDDFT Study

A series of metal‐free organic donor–π bridge–acceptor dyes are studied computationally using density functional theory (DFT) and time‐dependent DFT (TDDFT) approaches to explore their potential performances in dye‐sensitized solar cells (DSSCs). Taking triphenylamine (TPA) and cyanoacrylic acid moieties as donor and acceptor units, respectively, the effects of different substituents of the π linkers in the TPA‐based dyes on the energy conversion efficiency of the DSSCs are theoretically evaluated through optimized geometries, charge distributions, electronic structures, simulated absorption spectra, and free energies of injection. The results show that the molecular orbital energy levels and electron‐injection driving forces of the TPA dyes can be tuned by the introduction of substituents with different electron‐withdrawing or ‐donating abilities. The electron‐withdrawing substituent always lowers the energies of both frontier orbitals, while the electron‐donating one heightens them simultaneously. The efficiency trend of these TPA derivatives as sensitizers in DSSCs is also predicted by analyzing the light‐harvesting efficiencies and the free energies of injection. The following substituents are shown to increase the efficiency of the dye: OMe, OEt, OHe, and OH.     

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Soft X‐ray emission (XE), absorption (XA), and resonant inelastic scattering (RIXS) experiments have been conducted at the nitrogen K‐edge of urea and its derivatives in aqueous solution and were compared with density functional theory and time‐dependent density functional theory calculations. This comprehensive study provides detailed information on the occupied and unoccupied molecular orbitals of urea, thiourea, acetamide, dimethylurea, and biuret at valence levels. By identifying the electronic transitions that contribute to the experimental spectral features, the energy gap between the highest occupied and the lowest unoccupied molecular orbital of each molecule is determined. Moreover, a theoretical approach is introduced to simulate resonant inelastic X‐ray scattering spectra by adding an extra electron to the lowest unoccupied molecular orbital, thereby mimicking the real initial state of the core‐electron absorption before the subsequent relaxation process.     

Structural and spectroscopic characterization of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid with experimental techniques and quantum chemical calculations

In this study, the molecular conformation, vibrational and electronic transition analysis of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid (C7H4F2O2) were presented using experimental techniques (FT-IR, FT-Raman and UV) and quantum chemical calculations. FT-IR and FT-Raman spectra in solid state were recorded in the region 4000-400 cm(-1) and 4000-5 cm(-1), respectively. The UV absorption spectra of the compounds that dissolved in ethanol were recorded in the range of 200-800 nm. The structural properties of the molecules in the ground state were calculated using density functional theory (DFT) and second order M?ller-Plesset perturbation theory (MP2) employing 6-311++G(d,p) basis set. Optimized structure of compounds was interpreted and compared with the earlier reported experimental values. The scaled vibrational wavenumbers were compared with experimental results. The complete assignments were performed on the basis of the experimental data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. A study on the electronic properties, such as absorption wavelength, excitation energy, dipole moment and frontier molecular orbital energy, were performed by time dependent DFT (TD-DFT) approach. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands of steady compounds were discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules.     

Ferrocene‐Donor and 4,5‐Dicyanoimidazole‐Acceptor Moieties in Charge‐Transfer Chromophores with π Linkers Tailored for Second‐Order Nonlinear Optics

A series of new nonlinear optical chromophores ( 1 – 15 ) that were comprised of ferrocene‐donor and 4,5‐dicyanoimidazole‐acceptor moieties and various π linkers of different length were synthesized. Support for the presence of significant D ? A interactions in these NLO‐phores was obtained from the evaluation of the quinoid character of the 1,4‐phenylene moieties and their electronic absorption spectra, which featured intense high‐energy (HE) bands that were accompanied by less‐intense low‐energy (LE) bands. The redox behavior of these compounds was investigated by cyclic voltammetry (CV) and by rotating‐disc voltammetry (RDV); their electrochemical gaps decreased steadily from 2.64 to 2.09 V. In addition to the experimentally obtained data, DFT calculations of their absorption spectra, HOMO/LUMO levels, and second‐order polarizabilities (β) (?2ω,ω,ω) were performed. A structure–property relationship study that was performed by systematically altering the π linker revealed that the intramolecular charge‐transfer and nonlinear optical properties of these inorganic–organic hybrid D? π? A systems ( 1 – 15 ) were primarily affected by: 1) The presence of olefinic/acetylenic subunits; 2) the length of the π linker; and 3) the spatial arrangement (planarity) of the π linker.     

Intramolecular electronic communication in a dimethylaminoazobenzene–fullerene C60 dyad: An experimental and TD‐DFT study

An electronically push–pull type dimethylaminoazobenzene–fullerene C₆₀ hybrid was designed and synthesized by tailoring N,N‐dimethylaniline as an electron donating auxochrome that intensified charge density on the β‐azonitrogen, and on N‐methylfulleropyrrolidine (NMFP) as an electron acceptor at the 4 and 4′ positions of the azobenzene moiety, respectively. The absorption and charge transfer behavior of the hybrid donor‐bridge‐acceptor dyad were studied experimentally and by performing TD‐DFT calculations. The TD‐DFT predicted charge transfer interactions of the dyad ranging from 747 to 601 nm were experimentally observed in the UV‐vis spectra at 721 nm in toluene and dichloromethane. A 149 mV anodic shift in the first reduction potential of the N?N group of the dyad in comparison with the model aminoazobenzene derivative further supported the phenomenon. Analysis of the charge transfer band through the orbital picture revealed charge displacement from the n_(N?N) (nonbonding) and π _(N?N) type orbitals centered on the donor part to the purely fullerene centered LUMOs and LUMO+n orbitals, delocalized over the entire molecule. The imposed electronic perturbations on the aminoazobenzene moiety upon coupling it with C₆₀ were analyzed by comparing the TD‐DFT predicted and experimentally observed electronic transition energies of the dyad with the model compounds, NMFP and (E)‐N,N‐dimethyl‐4‐(p‐tolyldiazenyl)aniline (AZNME). The n_(N?N) → π*_(N?N) and π_(N?N) → π*_(N?N) transitions of the dyad were bathochromically shifted with a significant charge transfer character. The shifting of π_(N?N) → π*_(N?N) excitation energy closer to the n → π*_(N?N) in comparison with the model aminoazobenzene emphasized the predominant existence of charge separated quinonoid‐like ground state electronic structure. Increasing solvent polarity introduced hyperchromic effect in the π_(N?N) → π*_(N?N) electronic transition at the expense of transitions involved with benzenic states, and the extent of intensity borrowing was quantified adopting the Gaussian deconvolution method. On a comparative scale, the predicted excitation energies were in reasonable agreement with the observed values, demonstrating the efficiency of TD‐DFT in predicting the localized and the charge transfer nature of transitions involved with large electronically asymmetric molecules with HOMO and LUMO centered on different parts of the molecular framework. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

线型和星型平面噻吩类低聚物衍生物分子结构及光电性质研究

运用密度泛函DFT B3LYP／6-31G(d)方法对线型(a)和星型(b)平面噻吩类低聚物衍生物分别进行了几何构型优化,并采用含时密度泛函TD-DFT B3LYP／6-31G(d)方法计算了其紫外吸收光谱．计算结果表明:用TD-DFT．方法计算体系的紫外吸收光谱值与实验数据吻合;通过对噻吩类低聚物衍生物分子几何结构和前线分子轨道能级的分析,并从理论上解释了线型(a)和星型(b)衍生物光谱性质的差异:后者与前者相比较吸收光谱发生红移,这是由于星型结构使其相应HOMO能级升高,电离能(IP)降低,成为很好的电子给体和空穴传输材料．     

DFT study of the physicochemical characteristics and spectral behavior of new 8‐substituted 1,3,7‐trimethylxanthines

Nine biologically active theophylline derivatives were investigated using quantum chemical methods (density functional theory level). All calculations were performed at B3LYP/6‐31G** level of theory. The electrostatic potential charges, highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) gap, dipole moment, vibration frequencies, and electronic spectra were calculated. Log P was determined by Ghose‐Crippen method. All of the compounds under study are polar and negatively charged, which is necessary for their interaction with the receptors/enzymes. Majority of the compounds are lipophilic and they can easily diffuse through the cell membrane. The observed differences between the calculated and the experimental vibration frequencies in the Fourier Transform Infrared Spectroscopy (FTIR) spectra are established to be mainly in NH and OH bands, due to hydrogen bonds formation. The discrepancies between theoretical and experimental electronic spectra may be due to vibration effects and H‐bonding with the solvent molecules. The obtained results show that this type of spectrum is formed mainly by the xanthine fragment of the molecule, especially in the fingerprint region. All calculated properties could be useful for future qualitative‐structure activity relationship (QSAR) analysis. © 2012 Wiley Periodicals, Inc.     

Design of high‐performance chlorine type dyes for dye‐sensitized solar cells

Intrinsic defect of electronic structure for the chlorine‐type porphyrin 1, which was synthesized for use in dye‐sensitized solar cell (DSSC), is found by theoretical calculation including density functional method (DFT), time‐dependent DFT, and C+/C? function. It is believed that the limited cell performance obtained by using dye 1 as the sensitizer is due to the existence of this electronic defect. To avoid this defect, a series of novel molecules with electron deficient π bridge were designed. The subsequent theoretical calculation indicated that the electron deficient π bridge in the newly designed molecule is quite effective in offsetting the electronic defect observed for dye 1. The parameters for the designed molecules closely associated with open‐circuit voltage and short‐circuit current density including dipole moment of dye vertical to the surface of semiconductor and light‐harvesting efficiency were then evaluated. By comparing these parameters of designed dyes with those of dye 1, we can predict that the DSSC based on dye 4 (2, 6‐cyan benzoic acid as anchoring group) should possess enhanced performance, which would be a valuable theoretical guidance for the practical work. © 2013 Wiley Periodicals, Inc.     

Tuning the Electronic Properties of the Dative N−B Bond with Associated O−B Interaction: Electron Localizability Indicator from X‐Ray Wavefunction Refinement

Despite the immense growth in interest in difluoroborate dyes, the nature of the interactions of the boron atom within the N‐BF₂‐O kernel is not yet fully understood. Herein, a set of real‐space bonding indicators is used to quantify the electronic characteristics of the dative N?B bond in difluoroborate derivatives. The atoms‐in‐molecules (AIM) partitioning scheme is complemented by the electron localizability indicator (ELI‐D) approach, and both were applied to experimental and theoretical electron‐density distributions (X‐ray constrained wavefunction fitting vs. DFT calculations). Additionally, Fermi orbital analysis was introduced for small DFT models to support and extend the findings for structures that contain BF₂.     

Experimental and theoretical study of the electronic absorption spectra of some 1,2‐benzoquinone diazides: Closed–open tautomerism

The electronic absorption spectra as well as molecular orbital (MO) calculations at the ab initio level of some 1,2‐benzoquinone diazides have been studied. The results of spectral study support the open isomer over the closed one (1,2,3‐oxadiazole derivative) and indicate the contribution of both the benzenoid and quinonoid structures to the molecule. Spectral results were confirmed by MO calculations. The results of the latter gave a lower total energy for a benzoquinone diazide than for 1,2,3‐benzoxadiazole structure. Bond length and charge density indicate the contribution of both quinonoid and benzenoid structures for the studied compounds. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 52–62, 2000     

Silicon‐Containing Formal 4π‐Electron Four‐Membered Ring Systems: Antiaromatic,Aromatic, or Nonaromatic?

Density functional theory calculations (B3LYP) have been carried out to investigate the 4π‐electron systems of 2,4‐disila‐1,3‐diphosphacyclobutadiene (compound 1 ) and the tetrasilacyclobutadiene dication (compound 2 ). The calculated nucleus‐independent chemical shift (NICS) values for these two compounds are negative, which indicates that the core rings of compounds 1 and 2 have a certain amount of aromaticity. However, deep electronic analysis reveals that neither of these two formal 4π‐electron four‐membered ring systems is aromatic. Compound 1 has very weak, almost negligible antiaromaticity, and the amidinate ligands attached to the Si atoms play an important role in stabilizing this conjugated 4π‐electron system. The monoanionic bidentate ligand interacts with the conjugated π system to cause π‐orbital splitting. This ligand‐induced π‐orbital splitting effect provides an opportunity to manipulate the gap between occupied and unoccupied π orbitals in conjugated systems. Conversely, compound 2 is nonaromatic because its core ring does not have a conjugated π ring system and does not fulfill the requirements of a Hückel system.     

9,9′-螺双芴的光电性能

采用密度泛函理论(DFT)-B3LYP/6-31G(d)方法对9,9'-螺双芴低聚物[(SBF)_n(n=1-4)]体系进行全优化,得到各分子的最高占据轨道(HOMO)和最低空轨道(LUMO)能量及HOMO-LUMO能隙,结果表明各分子整体表现出很好的共轭性质.并在分子的阳离子和阴离子状态的优化结构基础上,计算得到电离势(IP)、电子亲和势(EA)、空穴抽取能(HEP)、电子抽取能(EEP)和重组能等相关能量.利用单激发组态相瓦作用(CIS)/3-21G方法优化得到9,9'-螺双芴单体的S_1激发态的几何构型.用含时密度泛函理论(TD-DFT)方法计算得到了分子吸收光谱和荧光光谱的相关数据.随着聚合长度的增加,能隙变窄,空穴注入和电子转移的能力都相应提高,吸收光所需能量减小,吸收强度(f)增大,光谱红移.采用线性外推法,利用低聚物分子的各种性质与聚合度n之间的关系,得到高聚物的相应性质.为考察9位螺芴化的影响,将(SBF)_n的相关性质与母体芴的低聚物[(FL)_n(n=1-4)]进行比较,由两者的计算结果对比显示,在芴的9位螺芴化可以提高电子和空穴的传输能力,并同时保留芴优良的发光性质.     

A density functional study of 1,1,5‐tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene

The optimized molecular structural parameters and UV‐vis, IR and Raman spectra of a dye molecule with an open formula of 1,1,5‐Tris(4‐dimethylaminophenyl)‐3‐methyl‐divinylene are determined by means of density functional theory (DFT) calculations using B3LYP/6‐31G** formalism. Neutral and cationically charged molecules are used for DFT computations. C? C, C?C, and N? C bond distances of dimethylaminophenyl groups of the dye molecule are in reasonable agreement with the experimental and theoretical C? C, C?C, and N? C bond lengths of the group reported in the literature. Because Vis‐NIR region is near UV‐Vis region in the electromagnetic spectra, calculated maximum wavelengths of UV‐vis spectra are close to those of the experimental VIS‐NIR spectra reported. C?C stretching frequencies calculated for dimethylaminophenyl, alkene, and benzene ring groups are also in good agreement with experimentally reported values. All calculated frequencies fall within 2.2% of the experimental frequency region. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Thienoacene‐Fused Pentalenes: Syntheses,Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene‐fused pentalene derivatives ( 1 – 3 ) with different π‐conjugation lengths were synthesized. X‐ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field‐effect transistors (OFETs) were also investigated. The highest field‐effect hole mobility of 0.016, 0.036 and 0.001 cm² V^?1 s^?1 was achieved for solution‐processed thin films of 1 – 3 , respectively.     

蒽醌及其羟基衍生物的密度泛函理论研究

运用密度泛函理论, 在B3LYP/6-31G*水平上, 对蒽醌及其羟基取代衍生物进行理论计算. 几何全优化的结果表明, 标题化合物均取平面构型, 分子内氢键对几何构型和电子结构影响很大. 基于简谐振动分析求得IR谱频率和强度, 并作了对称性分类和指认, 计算值与实验值良好相符. 运用含时密度泛函理论方法在相同水平上计算了标题物的电子吸收光谱, 发现蒽醌芳环取代衍生物的最低激发单重态均源自HOMO-LUMO(π→π*)跃迁. 基于振动分析, 由统计热力学求得了标题物的热力学性质.     

UV‐induced crosslinking of ring opening metathesis block copolymer micelles

Statistical and amphiphilic block copolymers bearing cinnamoyl groups were prepared by ring opening metathesis polymerization (ROMP). The UV‐induced [2 + 2] cycloaddition reaction of polymer bound cinnamic acid groups was studied in polymer thin films as well as in block copolymer micelles. In both cases, exposure to UV‐light for 10 min led to a crosslinking conversion of about 60%, as determined by FT‐IR spectroscopy and UV–vis absorption measurements. Time based IR‐spectroscopy revealed a maximum conversion of 78% reached after an irradiation time of about 16 min. For micelles obtained from polymers bearing 5 mol % or more cinnamoyl groups, the crosslinking reaction proceeded smoothly, yielding in crosslinked particles which were stable in a non‐selective solvent (CHCl₃). Diameters determined by dynamic light scattering in the selective solvent (MeOH) were similar for both, non‐crosslinked and crosslinked micelles, whereas diameters of crosslinked micelles in the non‐selective solvent (CHCl₃) were significantly larger compared to MeOH samples. This strategy of direct self assembly of block‐copolymers in a selective solvent followed by “clean” crosslinking, without the need for additional crosslinking reagents or crosslinking initiators, provides a straight forward approach toward ROMP‐based polymeric nano‐particles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2402–2413, 2008     

Probing the electronic structure,chemical bonding,and excitation spectra of [CuE]+/0/− (E = 14 group element) diatomics employing DFT and ab initio methods

The electronic structure, chemical bonding, and excitation spectra of neutral, cationic, and anionic diatomic molecules of Cu and 14 group elements formulated as [CuE]^+/0/? (E = C, Si, Ge, Sn, Pb) were investigated by density functional theory (DFT) and time‐dependent (TD)‐DFT methods. The electronic and bonding properties of the diatomics analyzed by natural bond orbital (NBO) analysis approch revealed a clear picture of the chemical bonding in these species. The spatial organization of the bonding between Cu and E atoms in the [CuE]^+/0/? (E = Si, Ge, Sn, Pb) molecules can easily be recognized by the cut‐plane electron localization function representations. Particular emphasis was given on the absorption spectra of the [CuE]^+/0/? which were simulated using the results of TD‐DFT calculations employing the hybrid Coulomb‐attenuating CAM‐B3LYP functional. The absorption bands have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2012 Wiley Periodicals, Inc.