Identification of fluorogenic and quenched benzoxadiazole reactive chromophores

The Sharpless–Meldal reaction was employed to generate triazole-substituted, alkynyl, azido and triazolyl-benzoxadiazole as well as nitro-benzoxadiazole fluorophores. Linkage of the triazole to the benzoxadiazole ring at C4 gave chromophores which were fluorogenic, while attachment through N1 resulted in quenching. The 4-azido-7-nitrobenzoxadiazole underwent a 470–fold decrease in quantum yield upon conversion to the triazole. While, 5-ethynyl-benzoxadiazole exhibited a 48–fold enhancement of quantum yield upon formation of triazole. The modulating effects of solvent polarity, conjugation, and attachment point of the fluorochrome to the triazole were examined.