Exploration of high-performance light-conversion agents based on cyanostilbene and phenanthrenecarbonitrile backbones: E/Z and position isomerism, high-contrast Michael addition reaction activity and intramolecular photocyclization

As light-conversion agents, traditional organic fluorescent dyes easily suffer from solid-state fluorescence quenching and photooxidation, leading to the deterioration of their application performance. To enhance the fluorescence emission and photostability of light-conversion agents in a doped film, in this paper, some luminogens with a cyanostilbene or a phenanthrenecarbonitrile backbone were designed and synthesized based on aggregation-induced emission (AIE) theory, E/Z isomerization and our previous research results, and were characterized via NMR, HR-MS and single-crystal X-ray diffraction. The experimental results indicate that both Z-oCa and Z-pCa exhibit high-contrast Michael addition reaction activity and intramolecular photocyclization, as well as fluorescence quantum yields in the doped film, but similar E/Z photoisomerization and AIE activity. Besides, E-oCa shows stable configuration in solution, but not for Z-pCa, meanwhile, E-oCa and Z-oCa display different AIE activities. More importantly, C-Ca with a twisted molecular configuration succeeded in avoiding fluorescence quenching induced by intramolecular photocyclization, emitting strong fluorescence in the solid state and the PABT-doped film (PLQY = 0.65). After an intensified UV radiation of 20 h, 94% of the initial intensity is reserved, and emission peaks exhibit tiny shifts. Based on matching excitation and emission maxima (374 nm and 433 nm), high PLQY, excellent photostability and light-conversion quality in the doped film, C-Ca is a potential high-performance light-conversion agent. Finally, light-conversion properties and the intrinsic mechanism are discussed in detail using the UV-vis absorption spectra, fluorescence emission spectra, crystal analysis, the photosynthetic photon flux density, the percentages of different wavelength bands, theoretical calculations and XRD patterns. This work is the first report on a highly efficient light-conversion agent with the phenanthrenecarbonitrile backbone; meanwhile, it contributes considerably to the molecular design of photostable luminogens and basic photochemistry.