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Electronic structure of the two isomers of the anionic form of p-coumaric acid chromophore
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry. (Quantum Chemistry)ORCID iD: 0000-0001-7567-8295
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2011 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 3, 034310- p.Article in journal (Refereed) Published
Abstract [en]

A theoretical study of the electronic structure of the photoactive yellow protein (PYP) model chromophore, para-coumaric acid (p-CA), is presented. Electronically excited states of the phenolate and carboxylate isomers of the deprotonated p-CA are characterized by high-level ab initio methods including state-specific and multistate multireference pertrubation theory (SS-CASPT2, and MS-CASPT2), equation-of-motion coupled-cluster methods with single and double substitutions (EOM-CCSD) and with an approximate account of triple excitations (CC3). We found that the two isomers have distinctly different patterns of ionization and excitation energies. Their excitation energies differ by more than 1 eV, in contradiction to the experimental report [Rocha-Rinza et al., J. Phys. Chem. A 113, 9442 (2009)]. The calculations confirm metastable (autoionizing) character of the valence excited states of both phenolate and carboxylate isomers of p-CA in the gas phase. The type of resonance is different in the two forms. In the phenolate, the excited state lies above the detachment continuum (a shape resonance), whereas in the carboxylate the excited ππ* state lies below the π-orbital ionization continuum, but is above the states derived from ionization from three other orbitals (Feshbach resonance). The computed oscillator strength of the bright electronic state in the phenolate is higher than in the carboxylate, in agreement with Hückel's model predictions. The analysis of photofragmentation channels shows that the most probable products for the methylated derivatives of the phenolate and carboxylate forms of p-CA are CH3, CH2O and CH3, CH2O, CO2, respectively, thus suggesting an experimental probe that may discriminate between the two isomers.

Place, publisher, year, edition, pages
2011. Vol. 134, no 3, 034310- p.
National Category
Chemical Sciences
URN: urn:nbn:se:uu:diva-144782DOI: 10.1063/1.3516211ISI: 000286472200036PubMedID: 21261356OAI: oai:DiVA.org:uu-144782DiVA: diva2:394414
Available from: 2011-02-02 Created: 2011-02-02 Last updated: 2015-01-08Bibliographically approved

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