Structure affecting dissociation energy in polycyclic aromatic hydrocarbon ions

Abstract Steric interference of two bay-hydrogen atoms causes the benzo[c]phenanthrene radical cation to be non-planar. The energy required to remove one of these H atoms (2.8 ± 0.1 eV, from iPEPICO spectroscopy) is 1.5 eV lower than that required from the planar tetracene ion due to the formation of a new C C bond. This low dissociation energy precludes benzo[c]phenanthrene ions losing C 2 H 2 (observed from tetracene with an energy of 4.2 eV). The B3-LYP/6-311++G(2d,p) reaction pathways to C 2 H 2 loss are presented and found to be mediated by azulene-containing intermediates. The second IE of tetracene was measured to be 19.0 ± 0.2 eV.