Relative Stability of the La and Lb Excited States in Adenine and Guanine : Direct Evidence from TD-DFT Calculations of MCD Spectra

Fabrizio Santoro, Roberto Improta, Tobias Fahleson, Joanna Kauczor, Patrick Norman, Sonia Coriani

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The relative position of La and Lb ππ* 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 S0 -> La transition from the weak S0 -> Lb 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, La <Lb, is the correct one.
Original languageEnglish
JournalJournal of Physical Chemistry Letters
Volume5
Issue number11
Pages (from-to)1806-1811
Number of pages6
ISSN1948-7185
DOIs
Publication statusPublished - 2014
Externally publishedYes

Keywords

  • Spectroscopy
  • Photochemistry
  • Excited states

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