Raman excitation profile of a sterically protected diphosphene [ArPPAr] Original Research Article

The resonance Raman excitation profile (RREP) of the bis[2,6-di(m-xylyl)phenyl]P2 diphosphene (DxpPPDxp) in CDCl3 was measured in the region of overlap between the π–π∗ (368 nm) and n+–π∗ (459 nm) UV/visible electronic absorption bands. The PP stretch (622 cm−1) was enhanced much more strongly in resonance with the allowed π–π∗ than with the symmetry-forbidden n+–π∗. The observed differences are attributed to differences in the geometries of the excited states and to the different mechanisms of enhancement for resonance with allowed and forbidden electronic absorptions.