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

Abstract

Organic fluorophores containing paramagnetic nitroxides covalently 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 patterning process can be thermally reverted (‘erased’) by heating the film above the glass transition temperature of the polymer.

Fluorescence Activation and Enhancement with Photogenerated Radicals, Pre-fluorescent Probes and Silver Nanostructures

“…In the latter process, energy is intramolecularly transferred from the BODIPY 1o core to the TEMPO, sensitizing the alkoxyamine product to cleavage and the hydroxylamine product to oxidation resulting, in regeneration of 1. 6,56,61 The activation of probe 1 is reproducible in 1% polymethylmethacrylate (w/v) (PMMA) solutions and a progressive increase in emission intensity is observed. However, under the same optimized conditions, there is a 550% increase in emission intensity just after 6 minutes (Figure 18).…”

Fluorescence Activation and Enhancement with Photogenerated Radicals, Pre-fluorescent Probes and Silver Nanostructures

“…In the latter process, energy is intramolecularly transferred from the BODIPY 1o core to the TEMPO, sensitizing the alkoxyamine product to cleavage and the hydroxylamine product to oxidation resulting, in regeneration of 1. 6,56,61 The activation of probe 1 is reproducible in 1% polymethylmethacrylate (w/v) (PMMA) solutions and a progressive increase in emission intensity is observed. However, under the same optimized conditions, there is a 550% increase in emission intensity just after 6 minutes (Figure 18).…”