Photochemical Insights on Intramolecular Dye-Sensitized Free-Radical Processes with a Quinoline Antenna

摘要

Organic fluorophores containing paramagnetic nitroxides co- valently tethered to the chromophoric core show a dramatic reduction in fluorescence due to intramolecular quenching of their excited states. Nonetheless, trapping of hydrogen atoms or carbon-centered radicals by the nitroxide suppresses the quenching pathway and restores the fluorescence, an effect that can be used to monitor radical scavenging processes. Herein, we synthesized a prefluorescent radical probe in which a 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moiety was chemically coupled to a quinoline chromophore, which can directly sensitize TEMPO via energy transfer following low- intensity ultraviolet illumination. In this design, the quinoline dye effectively acts as molecular ‘antenna’ to promote the reactivity of TEMPO toward H abstraction to form the corresponding N-hydroxylamine. The excited TEMPO can also abstract a hydrogen from a polymeric matrix, enabling the photochemical modification of the polymer with concomitant fluorescence activation and patterning. In addition, the pattern- ing process can be thermally reverted (‘erased’) by heating the film above the glass transition temperature of the polymer.