Fig. 3.

Two versions of wavelength-selective two-color uncaging. (A) Absorption spectra of nitroaromatic (purple), DEAC (blue) and DEAC450 (red) caging chromophores. Note that microscope glass is normally opaque below 330 nm. (B) Irradiation of a mixture of nitroaromatic- and DEAC-caged compounds with λ₁ causes uncaging of both cages, whereas irradiation with λ₂ enables wavelength-selective photolysis of the DEAC caged compound. Typically, experiments with such chromophore mixtures feature essentially complete photolysis of the DEAC cage (i.e. the ‘long wavelength’) with λ₂ before applying λ₁ to the cells. (C) Irradiation of a mixture of nitroaromatic- and DEAC450-caged compounds with λ₁ or λ₃ produces wavelength-selective uncaging of either caged compound, no matter which wavelength of light is used first. Thus λ₁ and λ₃ can be applied in an arbitrary order such that photolysis with λ₁ can bracket photolysis with λ₃; see Olson et al. (2013a) and experiments herein.