Theoretical Calculations of Electronic Spectra

Ghosh and Almlof published many articles discussing the XPS (X-ray photoelectron spectroscopy) and UPS (ultraviolet photoelectron spectra) and the corresponding ionization potentials of porphyrins using high-level calculations. Tliese topics are indirectly related to the tautomerism of porphyrins (for an example see 94IC6057 and 95JA4691). 

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Much remains to be understood about the structure of solvents in solution and the degree of local order caused by interaction with the solute. In particular, theoretical calculation of electronic spectra of coordination compounds in the presence of solvent has been limited to a narrow range of complexes, and mainly to water as a solvent. 

When Jens Oddershede was elected a Fellow of the American Physical Society in 1993, the citation read For contribution to the theory, computation, and understanding of molecular response properties, especially through the elucidation implementation of the Polarization Propagator formalism. Although written more than a decade ago, it is still true today. The common thread that has run through Jens work for the past score of years is development of theoretical methods for studying the response properties of molecules. His primary interest has been in the development and applications of polarization propagator methods for direct calculation of electronic spectra, radiative lifetime and linear and non-linear response properties such as dynamical dipole polarizabilities and... 

Roos BO, Fiilscher MP, Malmqvist P-A, Merchan M, Serrano-Andres L (1996) Theoretical Studies of Electronic Spectra of Organic Molecules. In Langhoff SR (ed) Quantum Mechanical Electronic Structure Calculations with Chemical Accuracy, Kluwer, Dordrecht, p 357. 

As a model compound for the theoretical calculation of CD spectra, we adopted the molecule (12bS)-26 having the essential part of the Jt-electron system contained in the naphthalene-diene compounds 22-25.1 Namely, in addition to the naphthalene and conjugated diene chromophores, the lone-pair electrons of the two methyl ether and furan ring oxygens are also included. The absolute configuration of 26 was arbitrarily chosen to be 12b5 for the calculation. The molecular geo-... 

Theoretical calculations on the nature of solvent effects which affect the n-Jt blue shifts for pyrimidine, pyridazine, and pyrazine have been compared with the results of experimental observation . A theoretical study of electronic spectra and photophysics of uracil derivatives , the luminescence of 4-phenylpyridine and... 

B. O. Roos, M.P. Fulscher, P.-A. Malmqvist, M. Merchan and L. Serrano-Andres, Theoretical studies of electronic spectra of organic molecules, in S.R. Langhoff (Ed.), Quantum mechanical electronic structure calculations with chemical accuracy. Understanding Chemical Reactions, Kluwer, Dordrecht, 1995, pp. 357-438. 

Grkovic T, Ding Y, Li X-C, Webb VL, Ferreira D, Copp BR (2008) Enantiomeric discorhabdin alkaloids and establishment of their absolute configurations using theoretical calculations of electronic circular dichroism spectra. J Org Chem 73 9133-9136... 

As HF and DFT procedures are based on a variational principle, they can only obtain the lowest energy of the molecular system. To obtain the energies of excited electronic states (and so be able to study photochemical processes) it is necessary to go to a Cl calculation. The simple procedure is the Cl-singles (CIS) that just considers monoelectronic excitations [7]. A more precise technique is the complete active space (CAS) method that performs a full Cl over a selected (active) space of orbitals [8]. CAS methods are very powerful in the theoretical analysis of electronic spectra but are difficult to apply to reactivity as it is difficult to ascertain that the active space remains unchanged along all the reaction paths. Within the DFT formalism it is also possible to study excited electronic states using the time-dependent (TDDFT) formalism [9,10]. 

The phthalocyanines, naphthalocyanines, and certain of their metal derivatives (Figure 6.17) are infrared fluorophores. 61"64 As a class, they are exceptionally stable compounds, with copper (Cu) phthalocyanine (not a fluorophore) remaining intact above 300 °C in air. First used for textile dyeing in the last century and still widely used, there is a rich chemistry of phthalocyanines. Most derivatives can be made by prolonged heating of a phthalimide or phthalic acid derivative with a metal in powder or salt form at elevated temperature. Several derivatives absorb in the near-IR, and either fluoresce or phosphoresce. The electronic transitions of phthalocyanines are complex and have been extensively studied, at least in part because the symmetry of the molecule makes theoretical calculations of its spectroscopic behavior more tractable. Unsubstituted phthalocyanines and naphthalocyanines are, as a class, very insoluble in solvents other than, for instance, nitrobenzene. Sulfonated phthalocyanines are water soluble and exhibit spectra comparable to the parent derivative. Photolumines-cent phthalocyanines (Pcs) include SiPc, ZnPc, and PC itself. These compounds have been little used for practical infrared fluorometry to date however, Diatron Corpora-... 

There has been interest in the theoretical treatment of the spectra of the phenanthrolines. Correlations between nuclear magnetic resonance (NMR)42-48 and electronic spectra22,38,40 41,49-51 with various quantum chemical data have been discussed. Often there is reasonable agreement between the calculated and measured spectra. 

However, again, as in the case of calculations of energy spectra, it is much more efficient to use universal computer programs to perform accurate theoretical or semi-empirical calculations of electron transition and other properties and quantities of atoms or ions, particularly if they may be combined with the relevant experimental studies [187-191]. 

In this study we have described theoretical calculations, syntheses, optical spectra, ground-state dipole moment measurements, and measurements of molecular second-order hyperpolarizability coefficients (/J) for new stilbene and azobenzene derivatives containing a methylsulfonyl group as the electron acceptor. We have shown that theoretical calculations can be used to predict the ratio of molecular hyperpolarizabilities between similar compounds, and that these gas phase calculations underestimate /J, probably as a result of the valence basis set used in the calculations. 

On the basis of theoretical calculations of HOMO and LLJMO (using a PM3 Hamiltonian) as well as UV-Vis spectra, it was demonstrated that in the case of 1,3-dithietanes 28 having disilyl moieties, effective . 

Nakai K, Ishii K, Kobayashi N, Yonehara H, Pac C (2003) Theoretical calculations of the electronic absorption spectra of oxotitanium(IV) phthalocyanine in the solid State. J Phys Chem B 107(36) 9749-9755... 

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