Photochemical Insights on Intramolecular Dye‐Sensitized Free‐Radical Processes with a Quinoline Antenna. Issue 9 (4th March 2021)

• Record Type: Journal Article
• Authors: Akari, Aviya S.; Hodgson, Gregory K.; Golian, Karol P.; Impellizzeri, Stefania
• Is Part Of: ChemistrySelect. Volume 6:Issue 9(2021)
• Page Start: 2394
• Page End: 2399
• Publication Date: 2021-03-04
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.202100027
• Languages: English
• ISSNs: 2365-6549

Abstract

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. Abstract : Under mild ultraviolet illumination, a quinoline dye acts as a molecular 'antenna' to promote the reactivity of chemically coupled TEMPO toward H abstraction to form the corresponding N ‐hydroxylamine. The hydrogen can also be abstracted from a polymer matrix (R), and subsequent linkage of the dye‐nitroxide to the polymer skeleton can occur. In all cases, the intramolecular quenching pathway is suppressed and the fluorescence of the quinoline dye is restored.