Theoretical studies on the structures and electronic spectra of C75B−

Intermediate neglect of differential overlap (INDO) calculations were used to study the structure of C₇₅B^?—the isoelectronic molecule of C₇₆. It was found that the boron atom mainly substitutes the second carbon atom (there are 19 types of carbon atoms in C₇₆). The electronic spectra of all the possible isomers of C₇₅B^? were calculated based on the optimized geometries. It was shown that the UV‐Vis spectra of C₇₅B^? and C₇₆ resemble each other in many ways with the exception of the absorptions beyond 700 nm. The red shift of the absorptions was rationalized and nature of transition of the peaks discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Studies of equilibrium geometries and electronic spectra for C78O4

Equilibrium geometries and relative stabilities of 24 possible isomers for C₇₈O₄ based on C₇₈ (C_2v) were studied by intermediate neglect of differential overlap (INDO) calculations. It was indicated that the most stable geometry is 28,29,30,31,52,53,73,78‐C₇₈O₄, where three oxygen atoms are added to the same hexagon, through which the longest axis of C₇₈ (C_2v) goes, and the forth oxygen atom is added to the C(73)? C(78) bond intersected by the shortest axis of C₇₈ (C_2v), and epoxide structures are formed. Electronic spectra of C₇₈O₄ isomers were investigated based on the optimized geometries. The blue shift of the first absorption for 28,29,30,31,52,53,73,78‐C₇₈O₄ compared with that of C₇₈ (C_2v) was rationalized and nature of transition for the peaks discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

C78O异构体的电子结构和光谱

The semi-empirical INDO method was used to study the electronic structures and the spectra of all of the 34 possible isomers of C78O based on C78 with group C2v. This calculation can simulate positions of an additional oxygen atom in C78 and predict the spectroscopic characteristics of the isomers. The most stable geometry of C78O is the 73,78-C78O molecule with an epoxide structure. The added 73,78-bond is located between two hexagons (6-6) and is intersected by the shortest C2 axis in C78 with group C2v. Atomic orbitals of the oxygen atom play an important role in lowering HOMO energy of 73,78-C78O. Compared with C78 with group C2v, the blue-shift in the electronic absorption spectrum for 73,78-C78O was observed.The reason of the blue-shift effect was discussed, and the electronic transitions were assigned based on the theoretical calculations.     

Stabilities and Electronic Spectra for C78O2 Isomers

1 INTRODUCTION Functional derivatives of fullerenes have aroused chemists’ interest and monofunctional products are accompanied by difunctional derivatives[1～3]. Diede- rich[1] prepared and detected C70O2 by the FAB mass spectrum. Kalsbeck[2] synthesized C60On (n = 1～4) by electrochemical oxidation of C60. Wood[3] investi- gated photolysis of a crude fullerene mixture and obtained C60On (n = 2～5) and C70O2. Menon[4] stu- died the optimized structures and electronic proper- ties o…     

Cn78(C2v)的电子结构和UV谱

用INDO(Intermediate neglect differential overlap)系列方法对Cn78进行系统研究.结果表明,Cn78(G2v)比Cn78(C2v')稳定;Cn78(C2v)和Cn78(C2v')未发生Jahn-Teller畸变;Cn78随n绝对值增大,体系能量升高.以优化构型为基础,首次计算Cn78电子光谱,对电子跃迁进行理论指认,讨论Cn78光谱特征吸收与C78相比发生红移的原因.     

Electronic Structure and Redox Properties of Metal Nitride Endohedral Fullerenes M3N@C2n (M=Sc,Y, La,and Gd; 2n=80, 84, 88, 92, 96)

An extensive study of the redox properties of metal nitride endohedral fullerenes (MNEFs) based on DFT computational calculations has been performed. The electronic structure of the singly oxidized and reduced MNEFs has been thoroughly analyzed and the first anodic and cathodic potentials, as well as the electrochemical gaps, have been predicted for a large number of M₃N@C_2n systems (M=Sc, Y, La, and Gd; 2n=80, 84, 88, 92, and 96). In particular, calculations that include thermal and entropic effects correctly predict the different anodic behavior of the two isomers (I_h and D_5h) of Sc₃N@C₈₀, which is the basis for their electrochemical separation. Important differences were found in the electronic structure of reduced M₃N@C₈₀ when M=Sc or when M is a more electropositive metal, such as Y or Gd. Moreover, the changes in the electrochemical gaps within the Gd₃N@C_2n series (2n=80, 84, and 88) have been rationalized and the use of Y‐based computational models to study the Gd‐based systems has been justified. The redox properties of the largest MNEFs characterized so far, La₃N@C_2n (2n=92 and 96), were also correctly predicted. Finally, the quality of these predictions and their usefulness in distinguishing the carbon cages for MNEFs with unknown structures is discussed.     

C_(78)~n(C_(2v))的电子结构和UV谱

用INDO (Intermediateneglectdifferentialoverlap)系列方法对Cn78进行系统研究 .结果表明 ,C78(C2v)比C78(C2v′)稳定 ;Cn78(C2v)和Cn78(C2v′)未发生Jahn Teller畸变 ;Cn78随n绝对值增大 ,体系能量升高 .以优化构型为基础 ,首次计算Cn78电子光谱 ,对电子跃迁进行理论指认 ,讨论Cn78光谱特征吸收与C78相比发生红移的原因 .     

Theoretical studies on structures and UV-Vis spectra of C_(70)O

Systematic studies on eight isomers of C70O were performed by means of INDO methods It has been indicated that the O atom is mainly added to the C1-C2 or C3-C3 bond and an epoxide feature with C1 symmetry is formed.Based on the optimized geometries,the UV-Vis spectra were calculated.It has been found that the main peaks of C70O resemble those of C70 and the characteristic absorptions beyond 460 nm are produced,which is m agree ment with the experimental results.Theoretical assignments about the absorptions were carried out and the reason for the red-shift of the absorptions was discussed.C70O is probably composed of four isomers according to the calculated results.     

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules

We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2‐thphCCM ( 1 ) and 3‐thphCCM ( 2 ), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2 . Theoretical calculations show the same trend. Self‐assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single‐molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.     

C78n离子的Jahn-Teller畸变和电子光谱

用INDO系列方法对C78n(D3、D3h、D?h)进行系统研究,表明C78(D3)比C78(D3h、D?h)稳定,与理论计算及实验结果一致;且随n绝对值增大,C78n总能量升高;C78n(D3、D3h、D?h)异构体的部分离子发生了Jahn-Teller畸变.以优化构型为基础,用INDO/SCI方法首次计算了C78n的电子光谱,对电子跃迁进行理论指认,讨论C78n光谱的特征吸收与C78相比发生红移的原因.     

C70O2可能异构体的结构和电子光谱的理论研究

用AM1、PM3及INDO系列方法研究了C₇₀O₂可能异构体的结构和稳定性.在C₇₀O稳定构型的基础上,考察了C₇₀O₂的45种异构体.结果表明,两个O原子加在碳球极端处同一个六元环内不等价的6/6键上形成环氧结构的构型最稳定.在优化构型的基础上,进行电子光谱计算,并与C₇₀和C₇₀O进行了比较.     

The properties and possible transformation path for C12B24N24

The structure and frequencies of C₁₂B₂₄N₂₄ have been calculated by means of an ab initio method. By comparing the average bond energies with C₆₀, the calculated results predict that the cage C₁₂B₂₄N₂₄ is a stable molecule. The calculated results indicate that the cage molecule C₁₂B₂₄N₂₄ has a relative large HOMO–LUMO energy gap and a low rigidity. The structures and stability of six possible isomers of C₂B₄N₄ are used to suggest a possible transformation path from the pentagon CB₂N₂ to the C₁₂B₂₄N₂₄ materials. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 363–368, 2001     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

C60O3的结构和电子光谱的理论研究

用INDO系列方法对C₆₀O₃的可能构型进行研究,结果表明:环氧结构邻近的6-6键易发生进一步的加成反应.其中3个氧原子加在同一个六元环的6-6边上,形成环氧结构最稳定的C₃v构型,第3个氧原子加在2个环氧结构相邻的六元环的6-6边上的C₂、C_s构型也相当稳定,C₂、C_s构型的部分¹³C NMR谱与实验吻合.C₆₀O₃可能有较好的反应活性,其电子光谱属于理论预测.     

Theoretical studies on structures and UV-Vis spectra of C70O

Systematic studies on eight isomers of C₇₀O were performed by means of INDO methods. It has been indicated that the O atom is mainly added to the C₁-C₂ or C₃-C₃ bond and an epoxide feature with C_s symmetry is formed. Based on the optimized geometries, the UV-Vis spectra were calculated. It has been found that the main peaks of C₇₀O resemble those of C₇₀ and the characteristic absorptions beyond 460 nm are produced, which is in agreement with the experimental results. Theoretical assignments about the absorptions were canied out and the reason for the red-shift of the absorptions was discussed. C₇₀O is probably composed of four isomers according to the calculated results. Project supported by the National Natural Science Foundation of China.     

Investigation on stabilities and spectroscopy of C80O2 based on C80 (D5d) using density functional theory

The relative stabilities of the 17 possible isomers for C₈₀O₂ based on C₈₀ (D_5d) were studied using Becke three parameters plus Lee, Yang, and Parr's (B3LYP) method and 6‐31G (d) basis set in density functional theory. The most stable geometry of C₈₀O₂ was predicted to be 23,24,27,28‐C₈₀O₂ (A) with annulene‐like structures, where the additive bonds are those between two hexagons (6/6 bonds) near the equatorial belt of C₈₀ (D_5d). Electronic spectra of C₈₀O₂ isomers were calculated based on the optimized geometries using intermediate neglect of differential overlap (INDO) calculation. Compared with those of C₈₀ (D_5d), the first absorptions in the electronic spectra of C₈₀O₂ are blue‐shifted owing to the wide energy gaps. ¹³C nuclear magnetic resonance spectra and nucleus independent chemical shifts of the C₈₀O₂ isomers were computed at B3LYP/6‐31G level. The chemical shifts of the bridged carbon atoms in the epoxy structures of C₈₀O₂ compared with those of the bridged carbon atoms in the annulene‐like structures are changed upfield. Generally, the isomers with the annulene‐like structures of C₈₀O₂ are more aromatic than those with the epoxy structures. The addition of the oxygen atoms near the pole of C₈₀ (D_5d) is favorable to improving the aromaticities of C₈₀O₂. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical Studies on Stabilities and Spectroscopy of C78O5

The semi-empirical AM1 and INDO/CIS methods as well as density function theory were used to study equilibrium geometries and spectroscopic properties of the possible isomers of C78O5 based on C2v-C78. The most stable geometry of C78O5 is 28,29,30,31,52,53,70,71,73,78-C78O5(A) with one annulene-like structure and four epoxide structures. Compared with that of C2v-C78, the blue-shift in the electronic absorption spectra of C78O5 isomers is predicted. The reason for the blue-shift effect is discussed and the electronic transitions are assigned. The IR and NMR spectra of C78O5 are explored with the AM1 and B3LYP/6-31G methods based on the B3LYP/6-31G optimized geometries.     

Theoretical study of two‐dimensionally fused zinc porphyrins: DFT calculations

Electronic structures of D_4h square‐fused zinc porphyrin sheets of two types ( SA , SB ), where SA is a directly meso‐meso‐, β‐β‐, and β‐β‐linked array and SB is a directly β‐fused array, were compared using density functional theory (DFT). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of oligomeric SA _n are characteristically delocalized at the cyclooctatetraene‐like sites composed of β‐pyrrolic carbons and their nearest‐neighbor nitrogens. Those of oligomeric SB _n remain solitary monomeric features, reflecting weakly interacting porphyrin units. These two‐dimensionally (2D) square‐fused sheets, especially for SA _n, show effective reduction of both the HOMO–LUMO energy gaps (E_g) and the lowest Q‐like excitation energies because of LUMO's greater stabilization with increasing number of porphyrins than the corresponding one‐dimensionally (1D) linear‐fused tapes. To estimate the minimum value of E_g, the electronic band structures of the infinite‐fused SA _∞ and SB _∞ were examined in detail using modern periodic DFT. Results indicate a full metal for SA _∞, with HOMO and LUMO bands crossing the Fermi level, and a semiconductor with E_g ≈ 0.5 eV for SB _∞. Furthermore, the phonon modes and the electron–phonon coupling (EPC) constant of SA _∞ were calculated throughout the Brillouin zone using density functional perturbation theory (DFPT), yielding a weak EPC constant, λ = 0.35. Within the standard phonon‐mediated BCS mechanism, the superconducting transition temperature, T_c is demonstrated using the McMillan formula, predicting ≈0.5 K. Results show that SA _∞ will become a rare synthetic metal/superconductor without a metal‐insulator transition coming from Peierls lattice instability because it has no serious imaginary phonon modes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

A simple model for the calculation of HOMO and LUMO energy levels of benzocatafusenes

A simple model for the calculation of HOMO and LUMO energy levels of benzocatafusenes (i.e., molecules that are only constituted by mutually condensed benzene rings and without interior carbon atoms, which belong to three benzene rings) is presented. Using semiempirical AM1 method, 615 benzocatafusenes were studied (29 normal and 586 branched). The relation between energy and molecular structure was coded by the three Hückel parameters: Coulomb integral, bond integral, and secular x eigenvalue. Analytical functions for HOMO and LUMO energy levels in terms of x parameter were obtained for normal benzocatafusenes, and energies for branched benzocatafusenes were satisfactorily modelled by the introduction of a simple correction function into the analytical functions describing normal benzocatafusenes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012