Photoinduced step-growth polymerizations are an important avenue to soft matter materials. However, photopolymerizations are highly challenging to unpack into their individual reaction steps and to determine the efficiency of these individual steps as a function of wavelength. Herein, we introduce a combined synthetic and photochemical action plot methodology to isolate the two key reaction steps of a step-growth photo-Diels-Alder polymerization and independently map their wavelength-dependent quantum yields with monochromatic resolution. To characterize our system with the highest possible precision, we introduce a photochemical action plot method based on the absorption of a constant number of photons at each wavelength. Our specific photopolymer system is based on a bis-o-methylbenzaldehyde (oMBA) species where the two reaction sites are electronically connected. Our approach initially entails the selective synthesis of a mono-Diels-Alder adduct from the symmetrical difunctional oMBA, enabling the precise mapping of the blue-shift in wavelength-dependent reactivity between the first and second addition. Our final molecule represents a distinct system of five fused rings, which matches the macromolecular system.
Chambers et al. (Wed,) studied this question.