NPA6: A Molecule for Non‐Covalently Linked Radical‐Enhanced ISC and High‐Performance Photopolymerization with Afterglow

To harness electron spin exchange for radical-enhanced intersystem crossing (ISC), a typical strategy involves covalently attaching stable radicals to chromophores. Here, we introduce NPA6, synthesized by attaching heptanamide to N,N-diphenylnaphthalen-1-amine (NPA). NPA6 maintains the phosphorescent properties of NPA and exhibits unique photo-generated radical behavior that is absent in NPA. These radicals can further adsorb neutral molecules to form supramolecular assemblies. Compared to pristine NPA6, these assemblies exhibit nearly complete NMR proton signal suppression in the aromatic region, enhanced absorption near 400 nm, and reduced fluorescence intensity. Phosphorescence measurements at 77 K reveal stronger phosphorescence in the assemblies, with delayed excitation spectra confirming phosphorescence originating exclusively from neutral molecules, indicating successful noncovalent radical-enhanced ISC. As a photosensitizer in N,N-dimethylacrylamide polymerization, NPA6 achieves nearly 100% conversion at 100 ppm under 410 nm light and ambient conditions, exhibiting superior polymerization performance. Additionally, its afterglow makes it suitable as an in situ quality indicator for transparent coatings, suggesting its potential applications in photolithography.