Nanosecond and picosecond laser flash photolysis studies of 2,2'-dinitrodiphenylmethanes

Abstract

The transient absorption spectra of the 2,2'-dinitrodiphenylmethanes 1a-1c in solution were examined in the picosecond and nanosecond time ranges. The absorption bands, observed at 420-450 nm on 355 nm (18 ps) excitation of these compounds, were attributed to the nitronic acids 2a-2c, formed through the singlet-state- mediated intramolecular hydrogen abstraction and the triplet states of 1a-1c. Biradical intermediates, formed through the intramolecular abstraction of the benzylic hydrogen by the triplet excited state, were detected for 1a and 1b. Transient species produced following 355 nm (approximately 6 ns) pulse excitation of 1a-1c result in the formation of the corresponding nitronic acids 2a-2c, with absorption maxima around 415-430 nm. These nitronic acids are the precursors of the various products formed in the steady state irradiation of 1a-1c.