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Theoretical investigation of anthracene‐9,10‐endoperoxide vertical singlet and triplet excitation spectra
Author(s) -
Corral Inés,
González Leticia
Publication year - 2008
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.20949
Subject(s) - complete active space , chemistry , intersystem crossing , singlet state , excited state , density functional theory , coupled cluster , singlet fission , anthracene , triplet state , wave function , basis set , atomic physics , computational chemistry , photochemistry , physics , molecule , organic chemistry
The electronic absorption spectrum of anthracene‐9,10‐endoperoxide (APO) has been investigated by means of multiconfigurational multi‐state second order perturbation theory on complete active space self‐consistent field wavefunctions (MS‐CASPT2/CASSCF) and two single reference methods: time‐dependent density functional theory (TD‐DFT) and coupled cluster of second order (CC2). After testing several active spaces and basis sets, a CAS (14,12) active space together with an ANO‐S basis set was found an appropriate choice to describe the vertical singlet and triplet electronic states of APO. Unfortunately, TD‐DFT and CC2 methods cannot reproduce the MS‐CASPT2 and experimental spectrum. Our MS‐CASPT2//CASSCF(14,12)/ANO‐S calculations predict a predominant π* OO σ* OO character for the lowest singlet excited state S 1 at 3.85 eV. Accordingly, the lowest singlet state of APO should be responsible for homolysis of the endoperoxide group. The next two absorbing excited states, experimentally proposed to be responsible for singlet oxygen production and therefore connected to the biological interest of APO, have been computed vertically at 4.34 and 4.59 eV and assigned to π CC π* CC and π* OO π* CC transitions, respectively. The vertical triplet electronic spectrum follows the singlet vertical spectrum ordering. The high density of triplet and singlet excited states of different nature within few eV points to the possibility of intersystem crossings between potential energy surfaces of different multiplicity. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008