Photochemical reaction and diffusion of caged calcium studied by the transient grating

A photoreaction of caged calcium (Ca²⁺) was investigated by using the time-resolved transient grating (TG) method. The q²-dependent feature of the TG signal was analyzed based on a model that there are two parallel dissociation steps with different rates and Ca²⁺ is released promptly after the fracture of the caged compound. The TG signal representing the presence of Ca²⁺ was appeared by the volume contribution. Although the diffusion coefficients of Cg and the decomposed product are different without Ca²⁺, only one diffusion component was observed after the dissociation of CgCa²⁺, indicating that the caged compounds and Ca²⁺ diffuse together.