As described above, photoswitching of aza-diarylethene 9 induces formation of an aromatized zwitterionic state. This zwitterion inherits a positively charged pyrido[1,2-a]pyrimidin-5-ium ring and also a highly nucleophilic thiolate functional group (Figure ). Light irradiation thus leads to formation of a pronounced chemical reactivity and we were wondering if starting from the zwitterionic form we could generate radicals initiating radical polymerization upon continued light irradiation similar to zwitterionic merocyanines. In this way, light could be used as an external trigger ultimately controlling formation of a solid material in a timed fashion. We projected that photoswitching of 9 would first lead to formation of the thiolate, which would then form radicals and be able to initialize radical methyl acrylate (MA) polymerization by initial attack on the MA Michael system. The resulting radicals would then polymerize the material under continuous carbon-carbon bond formation. We tested different mixtures of aza-diarylethene 9 and MA and found suitable conditions in the range between 0.4 -13 mg of 9/mL MA and irradiation times with light of 365 nm (260 mW) or 367 nm (1 W) of under 4 h. Those mixtures remain liquid in the absence of light without any noticeable polymerization happening. To our delight, irradiation with 365 nm light did in fact induce polymerization e.g. within 2 h 40 min at a concentration of 0.7 mg 9/mL MA and a solid yellow material was obtained as a result (Figure ). The same irradiation conditions in the absence of 9 did not lead to any visible polymerization and only liquid MA monomers remained. Only much longer light irradiation duration of more than 17 h with 365 nm (260 mW) did ultimately result in radical polymerization of MA (see Supporting Figure ). Additionally, we wanted to understand if the polymerization initiating event was triggered by the excited state of open 9