Transient Isomerisation and Inverse Electronic Relaxation of Infrared Multiple-Photon Excited Pentafluoropyridine

Abstract

Pentafluoropyridine (PFP) undergoes fast structural isomerisation to fulvenes when irradiated with 9R(16) CO₂ laser line in the fluence range 0.5–1.5 J/cm². The unstable fulvenes slowly decay back to PFP in ms time scale. No detectable permanent dissociation of PFP was observed in the above low fluence experiments. However, by using focused CO₂ laser beam for the irradiation of PFP, an emission of light in the visible/near-UV was observed. The time evolution of the luminescence reveals three peaks at 390, 460 and 500 nm on a broad background emission of 300–680 nm. These bands are assigned to the fluorescence of PFP via inverse electronic relaxation (IER) and C₂ Swan bands. On prolonged irradiation of PFP in focused condition a small extent of permanent dissociation was observed with the major products as C₂F₄, a sooty yellow deposit and another compound presumed to be Dewar PFP.