Knowledge Bank

This report summarizes our study of transitions to the lowest $n\Pi \ast$ singlet states of hydrogen bonded monocyclic azines. Using fluorinated alcohols, it is found that like pyrimidene and pyridazine, the absorption spectrum of hydrogen bonded s-triazine is broad and structureless. This is interpreted to mean that all hydrogen bonded complexes of these molecules are unstable in $n\Pi \ast$ states. By contrast the $n\Pi \ast$ absorption spectrum of hydrogen bonded tetrazine retains considerable, detailed, vibronic structure in a manner similar to pyrazine. Results to date indicate that not only is the singly hydrogen bonded tetrazine complex stable in the lowest $n\Pi \ast$ excited state, but other complexes rosy be stable as well. A discussion of the vibronic spectrum of the lowest $n\Pi \ast$ state of hydrogen bonded tetrszine will be given. The effect of hydrogen bonding on vibrational frequencies in this state will also be discussed.