6533b863fe1ef96bd12c7891
RESEARCH PRODUCT
A theoretical study of the low-lying states of the anionic and protonated ionic forms of urocanic acid
Christopher S. PageMassimo OlivucciManuela Merchánsubject
Urocanic acidchemistry.chemical_compoundchemistryMoleculeIonic bondingProtonationSinglet statePhysical and Theoretical ChemistryPhotochemistryCis–trans isomerismSpectral lineIondescription
A multistate second-order perturbation theory (MS−CASPT2) study of the lowest lying states in the electronic spectra of urocanic acid in vacuo is presented. The anionic trans and cis isomers, as well as the biologically important trans protonated ionic structure, are considered. The vertical and 0−0 excitation spectra were computed for each system at the MS−CASPT2/ANO-L level, describing the lowest lying ππ* and nπ* singlet and triplet states. In all three systems, a weakly absorbing ππ* singlet state was observed at ∼4.0 eV in the vertical excitation spectrum, suggesting both a novel assignment and an alternative explanation for the previously described wavelength dependent photochemistry of this molecule. The trans anion vertical spectrum otherwise comprises three intense ππ* transitions, at 4.14, 4.59, and 5.00 eV, whereas that of the cis anion shows two, at 4.52 and 5.01 eV. Conversely, the vertical spectrum of the protonated trans system is dominated by a single, intensely absorbing ππ* state, comput...
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2000-09-01 |