Direct observation of the 2-fluorenylnitrene and 4-methoxyphenylnitrene reactions with water using picosecond kerr-gated time-resolved resonance raman spectroscopy

Abstract

A picosecond Kerr-gated time-resolved resonance Raman examination of the 2-fluorenylnitrene and 4-methoxyphenylnitrene reactions with water to form the singlet 2-fluorenylnitrenium and 4-methoxyphenylnitrenium ions, respectively, is given. Photolysis of 2-fluorenyl azide and 4-methoxyphenyl azide in mixed water/acetonitrile solvents both led to formation of transient species within a few picoseconds, and these were tentatively assigned to the 2-fluorenylnitrene and 4-methoxyphenylnitrene species, respectively. These arylnitrenes were observed to directly react with water to produce their respective singlet arylnitrenium ions. The decay of the 4-methoxyphenylnitrene species and its accompanying growth of the 4-methoxyphenylnitrenium ion were found to be much faster than the decay of the 2-fluorenylnitrene and its accompanying growth of its 2-fluorenylnitrenium ion, indicating these two different arylnitrenes have noticeably different chemical reactivity toward water. The 4- methoxyphenylnitrene species spectra displayed noticeable changes in its time-resolved Raman spectra as the solvent system is changed from pure acetonitrile to a mixed water/ acetonitrile solvent whereas the 2-fluorenylnitrene spectra displayed very little if any change. These results suggest hydrogen bonding with the methoxy moiety.