A photoregulated chelating agent has been synthesized. It is a photochromic azobenzene compound containing two iminodiacetic acid groups and can exists as cis and trans stereoisomers. The planar trans isomer does not bind zinc ions. On exposure to light of 320 nanometers, the trans isomer is converted to a nonplanar cis isomer, which, because of cooperativity between the two iminodiacetic acid groups, binds zinc ions with the value of the binding constant estimated to be 1.1 x 10(5) +/- 9.2 x 10(5) liters per mole at a ratio of one molecule of chelating agent to one zinc ion. The interconversion of the cis and trans isomers is reversible, suggesting possible application of this class of compounds as photoresponsive ion pumps.