Diazo-2 is a photoactivatable Ca²⁺ scavenger. Diazo-2 is a relatively weak chelator (K_d for Ca²⁺ = 2.2 µM), however, following flash photolysis at ~360 nm, cytosolic free Ca²⁺ rapidly binds to the diazo-2 photolysis product, which has a high affinity for Ca²⁺ (K_d = 73 nM).