Anilines have been shown to be especially susceptible to single-electron oxidation by excited triplet-state photosensitizers (3sens*), and thus, are good potential candidates to probe the oxidative properties of triplet-state chromophoric dissolved organic matter (3CDOM*). However, steady-state experiments tend to underestimate their rate of oxidation by 3CDOM* due to radical cation quenching (i.e., aniline●+ → aniline) by antioxidant moieties present in CDOM. We envisioned the potential utility of N-cyclopropylaniline (CPA) to overcome this limitation, as it is known to undergo spontaneous, irreversible cyclopropyl ring-opening after an initial single-electron oxidation. To test this, first a suite of CPA analogs was synthesized and then paired with an appropriate model sensitizer and antioxidant, or various CDOM isolates, to examine their reactivity and susceptibility to antioxidant quenching during steady-state photolysis experiments. Next, time-resolved measurements of CPA oxidation were obtained by laser flash photolysis through direct observation of 3sens* and CPA●+ lifetimes. Finally, CPA photolysis products were isolated by semi-preparative high-performance liquid chromatography and identified by a combination of high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy. Outcomes of this work, including CPA bimolecular rate constants, CPA●+ lifetimes, and identified ring-opened products, support the usefulness of cyclopropylanilines as single-electron transfer probes in photosensitized aqueous solutions.

Single-electron oxidation of N-cyclopropylanilines by triplet-state dissolved organic matter

2019 Spring National Meeting

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