Alternative source of emissive CIDEP in the TREPR spectra of benzophenone in alcohols

The flash photolysis EPR spectra of benzophenone (BP) in alcoholic solvents differ in terms of their chemically induced dynamic electron polarization (CIDEP) signatures when BP is photo-excited at different laser wavelengths. The difference is strongly dependent upon the concentration of BP and is attributed to the reaction of two BP triplet states to form a BP radical anion, BP radical cation pair which occurs on a timescale sufficiently rapid relative to relaxation in the BP triplet to transfer polarization into the resulting radicals. This polarized signal dominates the spectrum obtained by 266nm photo-excitation due to the much larger extinction coefficient of BP at this wavelength.