Very-low-lying electronic states result from n --> pi excitations in open-shell annulenes, annelated with alpha-dicarbonyl groups.
UB3LYP/6-31G* calculations find that alpha-dicarbonyl-annelated cyclopentadienyl radical 1 has a sigma ground state, which is formed by excitation of an electron from the in-phase combination of carbonyl lone-pair orbitals into the singly occupied pi orbital. Similarly, tetrakis-annelated cyclooctatetraene 3 is calculated to have very-low-lying singlet and triplet excited states, which result from excitations of electrons from the b1g combination of lone pair orbitals into the empty pi nonbonding MO of the COT ring.
Zhou
Xin
X
Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, Texas 76203-5070, USA.
Hrovat
David A
DA
Borden
Weston Thatcher
WT