Knowledge Bank

We have previously discussed the electronic absorption and fluorescence, spectra of hydrogen bonded tetrazine which suggests the existence of both singly and doubly hydrogen bonded species in the ground and lowest excited $n\pi \ast$ singlet state. We will present newly obtained fluorescence spectra in the region 540-650 nm which strongly support this earlier contention. In the region between 190 and 240 nm we have observed two weak, vibronic bands which shift together toward higher energy upon the addition of alchohol. This observation strongly suggests that these bands belong to a second previously unreported $n\pi \ast$ transition. The effect of hydrogen bonding on the broad $n\pi \pi \ast$ transition at 280 nm and on other spectral features in this region will also be discussed.