On the TD-DFT UV/vis spectra accuracy: the azoalkanes

Using an ab intio TD-DFT approach systematically accounting for the molecular surroundings effects, we have computed the n → π* absorption wavelength of 22 azoalkane derivatives. For the complete set of molecules, we propose a theoretical procedure able to reproduce the major auxochromic effects, and to deliver a mean absolute error of 5.8 nm (0.056 eV) with maximal deviations limited to 21 nm (0.20 eV). The impact of including in the model explicit solvent molecules is discussed as well. This contribution confirms that PCM-TD-PBE0 is a first-grade method for simulating the vertical absorption spectra of organic dyes.     

UV absorption spectra of 3-aminorhodanine derivatives

3-Aminorhodanine condenses readily with isothiocyanates to form unsymmetrical thioureas of the rhodanine series. The UV spectra of arylidene derivatives of 3-aminorhodanine consist of four bands: a short-wave band with a maximum up to 242 nm, a “thioamide” band with a maximum at 264–290 nm, a “dithiocarbonate” band with maxima at 290–370 nm, and a long-wavelength K band with maxima at 310–520 nm. The K absorption band is the most characteristic band for the arylidene derivatives of 3-aminorhodanine, and the maxima for 3′,5-diarylidene derivatives are generally shifted to the short-wave region, while the maxima for the 5-monoarylidene derivatives are usually shifted to the long-wave region.     

Temperature effect upon the UV absorption spectra of aniline derivatives

Cooling of aromatic amines in nonpolar media shows a disappearance of the absorption CT band. This disappearance suggests the existence of a different conformation of these molecules in the stiffening range.     

Highly unsaturated pyranone derivatives from the basidiomycete Junghuhnianitida

Four new highly unsaturated pyranone derivatives A–D (1–4), together with one known compound 5 (−)-nitidon were isolated from cultures of the fungus Junghuhnianitida. Planar structures of the new compounds were elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. Absolute configurations of the new compounds were determined on the basis of biosynthetic considerations and quantum chemistry theory. Compound 1 exhibited almost the same cytotoxic activities as cis-platin.     

UV spectra of some derivatives of 5,10-dihydrophenarsazine and 5,10-dihydrophenoxarsine

The long-wave band with a maximum above 300 nm in the UV spectra of substituted 5,10-dihydrophenarsazines is interpreted as a transition with intramolecular charge transfer in which the trivalent arsenic atom acts as an electron acceptor. The unshared pair of electrons of As(III) apparently makes its own contribution to the transitions at 240–280 nm.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 768–770, June, 1974.     

Successful application of TD-DFT in transient absorption spectra assignment

[Reaction: see text] Despite the wide application of time-resolved spectra technology in investigating various chemical and biological processes, it is still a great challenge to give an unambiguous spectra assignment for observed transient species, e.g., the curcumin-derived radicals. Here we report that time-dependent density functional theory with the B3LYP functional and an appropriate basis set can give reliable absorption spectra for carbon- and oxygen-centered radicals derived from curcumin, which indicates the potential of theoretical methods in helping assign transient spectra.     

A TD-DFT study of the absorption spectra of fast dye salts

The UV/visible spectra of a series of diazonium fast dyes have been evaluated by using a time-dependent density functional theory approach explicitly taking into account bulk solvation effects. Using the PBE0 functional with the 6-311G(2d,2p) atomic basis set, the agreement between theory and experiment is excellent for these cationic species. The effects on the spectra of chemical substitution are analysed.     

Thioindigo dyes: highly accurate visible spectra with TD-DFT

The structure and visible spectra of a large panel of thioindigo dyes and derivatives have been evaluated using a TD-PBE0/6-311+G(2d,p)//PBE0/6-311G(d,p) approach explicitly taking bulk solvent effects into account by means of the polarizable continuum model. The influence of the solvent characteristics, the trans-cis isomerization, and the chemical substitution on the benzene rings have been investigated. In addition, hemi-thioindigo dyes, thiazine-indigo, chromophore-like molecules, and selenoindigo have been considered. Though the relative oscillator strengths of the two allowed visible transitions in the nonplanar cis isomers are not always correctly reproduced by theory, the agreement between theoretical and experimental results is far above expectations. For the 170 cases studied, we obtained a mean unsigned error on the predicted lambda(max) limited to 6.9 nm or 0.03 eV, with only 6 (4) cases for which the difference exceeds 20 nm (0.10 eV). These errors are 1 order of magnitude smaller than what has previously been reported for indigoids. A linear correlation between the central double bond length and the lambda(max) has been established, while the bond length and vibrational frequency of the carbonyl groups do not correlate with the thioindigo color. The higher excitation energies of the cis conformers, compared to the trans structures, result from a less stabilized LUMO in the former case. Indeed, for cis thioindigo, the two electron-rich (in the excited state) carbonyl units lie close to each other.     

UV spectra of N-vinylpyrroles

Chemistry of Heterocyclic Compounds - The effect of the structure and the medium on the position and intensity of the absorption bands in the UV spectra that attest to the presence of a single...     

C60的一些氨基酸衍生物结构、光谱的理论研究

用INDO/2系列方法研究了C60与氨基酸加成产物的结构和UV谱, 表明两种加成产物异构体---[6, 6]闭环和[6, 5]闭环异构体, 均具有Cs对称性, 且[6, 6]闭环异构体具有更低的生成热,因而更稳定, 以优化构型为基础, 计算了化合物的UV谱, 与实验值一致, 同时对电子跃迁进行理论指认, 讨论了产物UV谱带红移的原因。     

The13C NMR, UV and IR spectra of 2-fluoropyridine methyl derivatives

¹³C NMR, UV, and IR spectra of methyl derivatives of 2-fluoropyridine have been recorded. The influence of the substituents on the spectral characteristics of the compounds has been discussed. The electronic spectra have been calculated by a modified INDO method. Transition energies, intensities, and assignments are compared with UV spectra.Department of Organic Chemistry, Academy of Economics, Pl-53 342 Wroclaw, Poland Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 763–773, June, 1999.     

Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives

The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region.     

A quantitative prediction of the electronic spectra of thiocarbonyl chromophores: TD-DFT versus SAC-CI

In this contribution, we set up a SAC-CI methodology to evaluate the n → π* and π → π* vertical transition energies of a series of thiocarbonyl derivatives. We show that Frozen-Core SAC-CI provides accurate vertical excitations energies. Nevertheless, in order to obtain converged results, the R2S2 unliked integrals have to be taken into account in L3-SAC-CI calculations. In addition, we present the comparative performances of three computational procedures, INDO/S, TD-DFT, and SAC-CI, for the calculation of valence excited states energies and it turns out that: (1) no tuning of the exact exchange (α) included in TD-DFT allows to consistently reproduce the SAC-CI results; (2) SAC-CI and TD-B3LYP both evaluate the n → π*, as well as the π → π* transition energies, with a similar accuracy. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

UV absorption spectra and reactivity of 4-oxo and 4-thioxo derivatives of 1,3-thiazane

The C=O groups in positions 4 of the molecules of 2-thioxo-1, 3-thiazan-4-one and 1,3-thiazane-2,4-dione do not possess ketonic properties. When 2-thioxo-1,3-thiazan-4-one is treated with hydrazine or its derivatives, hydrazinolysis takes place. When these substances react with P₂S₅, the C=O groups are replaced by C=S groups. The compounds formed possess thioketonic properties, which makes it possible to obtain derivatives of 4-imino-1,3-thiazane. The condensation of -chloropropionic acid with thiourea leads to 1,3-thiazane-2,4-dione and the previously unreported 2-imino-1,3-thiazan-4-one. The UV spectra of the substances synthesized are described.     

UV spectra of vinyl chalcogenides: Correlation with the photoelectron spectra

The electron absorption spectra of alkylvinyl chalcogenides (CH₂=CHEAlk, E = S, Se, Te) were analyzed with consideration of the photoelectron spectroscopic data. The following sequence of electronic transitions was found in their UV spectra:

TD-DFT investigation of triple-stranded helicates with bis(benzene-o-dithiolato) ligands

The electronic spectra of triple-stranded complexes of Ti(IV) with bis(benzene-o-dithiolato) ligands (H(4)-L(1)=1,2-bis(2,3-dimercaptobenzamido)ethane; H(4)-L(2)=1,2-bis(2,3-dimercaptobenzamido)benzene) were investigated at the TD-DFT level of theory employing B3LYP/LANL2DZ. The influence of the nature (aliphatic or aromatic) of the spacer bridging both {Ti(S(2)C(6)H(3))(3)} units on the absorptive features of the dinuclear complexes was also studied. B3LYP/LANL2DZ leads to spectra accounting for four absorption bands. At the lowest-energy region, the most important transitions are due to ligand-to-metal charge transfer (LMCT), in which out-of-plane ligand-centered orbitals and titanium-based MOs are involved. In going to the blue-region, a third band was detected with excitations showing an important contribution from ligand-to-ligand charge transfer (LLCT) and indeed, a combined LMCT+LLCT character has been considered. This observation seems to arise from a decrease in the metallic character of the LUMO-derivatives involved in the excitations. The origin of the absorption band at the highest-energy part of the spectrum is assigned to a LLCT. The influence of the nature of the spacer on the molar absorption coefficients (?) for this band has been clearly observed. The complex bearing aliphatic spacer shows ? of about 5 E+4 M(-1) cm(-1), while the one containing an aromatic spacer present a value of ? of about 2 E+5 M(-1) cm(-1).     

Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives

The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Moller-Plesset second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C(infinity v) symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.     

Coumarin derivatives for dye sensitized solar cells: a TD-DFT study

Time dependent density functional theory (TD-DFT) calculations have been carried out to study the electronic structure and the optical properties of five coumarin based dyes: C343, NKX-2311, NKX-2586, NKX-2753 and NKX-2593. We have found out that the position and width of the first band in the electronic absorption spectra, the absorption threshold and the LUMO energy with respect to the conduction band edge are key parameters in order to establish some criteria that allow evaluating the efficiency of coumarin derivatives as sensitizers in Dye Sensitized Solar Cells (DSSC). Those criteria predict the efficiency ordering for the coumarin series in good agreement with the experimental evidence. Presumably, they might be used in the design of new efficient organic based DSSC.