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Relative Stability of the L-a and L-b Excited States in Adenine and Guanine: Direct Evidence from TD-DFT Calculations of MCD Spectra
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Italy .
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR).
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
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2014 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 11, 1806-1811 p.Article in journal (Refereed) Published
Abstract [en]

The relative position of L-a and L-b pi pi* electronic states in purine nucleobases is a much debated topic, since it can strongly affect our understanding of their photoexcited dynamics. To assess this point, we calculated the absorption and magnetic circular dichroism (MCD) spectra of adenine, guanine, and their nucleosides in gas-phase and aqueous solution,. exploiting recent developments in MCD computational technology within time-dependent density functional theory. MCD spectroscopy allows us to resolve the intense S-0 -greater than L-a transition from the weak S-0 -greater than L-b transition. The spectra obtained in water solution, by using B3LYP and CAM-B3LYP functionals and describing solvent effect by cluster models and by the polarizable continuum model (PCM), are in very good agreement with the experimental counterparts, thus providing direct and unambiguous evidence that the energy ordering predicted by TD-DFT, L-a less than L-b, is the correct one.

Place, publisher, year, edition, pages
American Chemical Society , 2014. Vol. 5, no 11, 1806-1811 p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-108796DOI: 10.1021/jz500633tISI: 000337012500005OAI: diva2:732917
Available from: 2014-07-07 Created: 2014-07-06 Last updated: 2016-01-15
In thesis
1. Development and characterization of damped cubic response functions with application to two-photon absorption
Open this publication in new window or tab >>Development and characterization of damped cubic response functions with application to two-photon absorption
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Molecular response to electromagnetic fields - static or optical - within a framework of perturbation theory diverges close to resonance with molecular transitionen energies, and need work-around solutions for real-valued response functions. This licentiate thesis deals with nonlinear response, with focus being on cubic polarizaibilities, and outlines the underlying mathematics for exact-state and approximatestate, complex-valued response functions applicable to quantum chemical computation. Such a complex-valued response theory is commonly known as dampedresponse theory, for which the response functions consists of a real and an imaginary component, each of them representing various spectroscopies in nature. In addition to the mathematics, the formulas have been implemented in the quantum chemical package DALTON, and several tests determining the integrity of the implementation has been conducted.

The fourth and final major part of the thesis is concerned with applied nonlinear response theory, including not only cubic response functions, but also quadratic and linear response functions, some of which are of the more exotic character. Three spectroscopies have been investigated for small and medium-sized organic molecules and the neon atom: two-photon absorption (TPA), Jones birefringence (JB), and magnetic circular dichroism (MCD).

The TPA part is a simple demonstration of capability of the damped cubic response code, for which neon is the example system. Perfect agreement is shown for the Ehrenfest approach and an independent implementation based on the quasienergy formalism.

JB is an optical eect in which induced refractive anisotropy, by means of external electric and magnetic static elds, results in ellipticity of linearly polarized light beams. This part mainly discuss implications from a paper which the current author took part in. The paper ultimately attempts to indentify the general observable strength of the effect, and coincidentaly pin-point some particular system suitable for experiments. Among other finds, JB is found to be correlated to the electric dipole moment, and for monosubstituted benzenes, the para-Hammett constant.

Finally, MCD is discussed based on three papers in which the present author is included. The elegant MCD solution to broad absorption peaks, for which it is desired to distinguish individual states, is demonstrated on adenine and three additional purine derivatives. A drawn out debate regarding relative stability of certain low-lying states could be settled by this method. Furthermore, appropriate description of solvation environment in conjunction with the exchange-correlation functionals B3LYP and CAM-B3LYP is investigated on purine and pyrimidine derivatives. CAM-B3LYP is found to be superior in terms of general prole shapes, while results regarding solvation model are rather inconclusive, although the results suggests some level of solvation model is appropriate, such as a polarizable continuum model or explicit solvation molecules.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 67 p.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1742
National Category
Theoretical Chemistry Chemical Sciences
urn:nbn:se:liu:diva-123972 (URN)978-91-7685-844-8 (Print) (ISBN)
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-15Bibliographically approved

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