Direct Observation of Acyl Azide Excited States and Their Decay Processes by Ultrafast Time Resolved Infrared Spectroscopy

The photochemistry of three carbonyl azides was studied by ultrafast time-resolved IR spectroscopy. Benzoyl, 2-naphthoyl, and pivavoyl azides are promoted to upper excited states S(n) with 270 nm excitation in chloroform. The S(n) states decay in 300 fs to form both the carbonylnitrenes and the S(1) excited states. The decay of the S(1) states of the carbonyl azides correlates with the growth of isocyanates. Formation of carbonylnitrene from S(1) is at most a minor process if it happens at all. The quantum yields of azide decomposition of these azides with 270 nm light are close to unity in chloroform.