Role of the 3(ππ*) state in photolysis of lumisantonin: insight from ab initio studies
2011 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 26, 7815-7822 p.Article in journal (Refereed) Published
The CASSCF and CASPT2 methodologies have been used to explore the potential energy surfaces of lumisantonin in the ground and low-lying triplet states along the photoisomerization pathways. Calculations indicate that the (n pi*) state is the accessible low-lying singlet state with a notable oscillator strength under an excitation wavelength of 320 nm and that it can effectively decay to the (3)(pi pi*) state through intersystem crossing in the region of minimum surface crossings with a notable spin-orbital coupling constant. The 3(pi pi*) state, derived from the promotion of an electron from the pi-type orbital mixed with the sigma orbital localized on the C-C bond in the three-membered alkyl ring to the pi* orbital of conjugation carbon atoms, plays a critical role in C-C bond cleavage. Based on the different C-C bond rupture patterns, the reaction pathways can be divided into paths A and B. Photolysis along path A arising from C1-C5 bond rupture is favorable because of the dynamic and thermodynamic preferences on the triplet excited-state PES. Path B is derived from the cleavage of the C5-C6 bond, leading first to a relatively stable species, compared to intermediate A-INT formed on the ground state PES. path B is relatively facile for the pyrolytic reaction. The present results provide a basis to interpret the experimental observations.
Place, publisher, year, edition, pages
2011. Vol. 115, no 26, 7815-7822 p.
Biochemistry and Molecular Biology
IdentifiersURN: urn:nbn:se:kth:diva-37160DOI: 10.1021/jp203369bISI: 000292281300047ScopusID: 2-s2.0-79959795779OAI: oai:DiVA.org:kth-37160DiVA: diva2:432389
FunderSwedish e‐Science Research Center
QC 201108032011-08-032011-08-022012-05-23Bibliographically approved