Quenching of Aromatic Hydrocarbon Singlets by Alkyl Azides

Hexyl azide was found to be an efficient quencher of aromatic hydrocarbon fluorescence. The rate of fluorescence quenching is related to the singlet energy of the donor in accord with an endothermic collisional exchange energy transfer mechanism. Energy transfer by donors with low singlet energies is more efficient than expected for classical endothermic energy transfer as was previously observed for triplet sensitization of alkyl azides. Both singlet and triplet results are best explained by vertical energy transfer to a bent azide ground state generating a bent excited state. Singlet sensitization leads to decomposition of the azide with an efficiency similar to that for the direct photolysis.