8-Benzenesulfonyloxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pend ant cyclen (BS-caged-L-4, BS = benzenesulfonyl) was designed and synthesized as a "caged" derivative of a previously described Zn2+ fluorophore, 8-hydroxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L-4) (cyclen = 1,4,7,10-tetraazacyclododecane). In the absence of metal ions and in the dark, BS-caged-L-4 (10 mu M) showed negligible fluorescence emission at pH 7.4 (10 mM HEPES with l = 0.1 (NaNO3)) and 25 degrees C (excitation at 328 nm). Addition of Zn2+ induced an increase in the UV/vis absorption of BS-caged-L-4 (10 mu M) at 258 nm and a significant increase in fluorescence emission at 512 nm. These responses are results from the formation of Zn(H-1L4) by the hydrolysis of the sulfonyl ester at the 8-position of the quinoline unit promoted by the Zn2+-bound HO-. Improvement of cell membrane permeation in comparison with L-4 is also described.