Quenching of ketone triplet excited states by atmospheric halides

Abstract

The photosensitized chemistry of three aromatic ketones (xanthone, flavone, and acetophenone) and also of secondary organic aerosols (SOAs) arising from the photo-oxidation of naphthalene was investigated by means of transient absorption spectroscopy.

Aromatic Carbonyl and Nitro Compounds as Photosensitizers and Their Photophysical Properties in the Tropospheric Aqueous Phase

“…While xanthone (Figure S9c) shows an absorbance band at higher wavelengths (λ max = 594 nm), the time-resolved absorbance spectra of the excited triplet states of benzophenone and 4-benzoylbenzoic acid (Figure S9a and b) show two strong absorbance bands (λ 1,max = 330–384 nm, λ 2,max = 517–655 nm). The obtained absorbance spectra of 4-benzoylbenzoic acid and xanthone are in good agreement with the literature. ,,,,, …”

“…The obtained absorbance spectra of 4-benzoylbenzoic acid and xanthone are in good agreement with the literature. 46,47,49,51,84,87 A kinetic analysis of the absorbance maxima of the respective photosensitizers was carried out to identify, especially in the case of benzophenone and 4-benzoylbenzoic acid, whether the absorbance maxima belong to the excited triplet state or to two different species. The kinetic analysis shows that the absorbance maxima of 4-benzoylbenzoic acid and xanthone can be assigned to their excited triplet states, whereas the absorbance maxima of benzophenone have different first-order decay rate constants k d and thus lifetimes (Table 1), indicating that two different species are observed.…”

“…This finding is in good agreement with the study by Woods et al (2020), who have shown that the triplet lifetime of imidazole-2-carboxaldehyde decreases with higher ionic strength. 109 For case (ii), electrolytes such as sulfate and chloride were considered as triplet quenchers although they, on the one hand, might be of low reactivity (k q = 10 5 L mol −1 s −1 ) 51,110 but, on the other hand, are present in very high concentrations under aerosol particle conditions (cf. Supporting Information).…”

Naphthalene‐Derived Secondary Organic Aerosols Interfacial Photosensitizing Properties

“…Naphthoquinone, a naphthalene oxidation product (McWhinney et al., 2013), is commonly found in atmospheric aerosols (e.g., Shanghai, China [Wang et al., 2017]; Tempe, USA [Delhomme et al., 2008]; Kurashiki City, Japan [Oda et al., 2001]; Yangtze River channel [Wang et al., 2020b]), and is known to be an efficient photosensitizer, inducing redox chemistry or producing reactive oxygen species (De Lucas et al., 2014; McNeill & Canonica, 2016). SOA derived from oxidation of naphthalene under high‐NO x conditions has been shown to be weakly fluorescent (Lee et al., 2014), resilient to photobleaching (Aiona et al., 2018), efficient in photosensitizing singlet oxygen in aqueous solutions (Manfrin et al., 2019), capable of photosensitized oxidation of halide ions (Gemayel et al., 2021), and moderately effective in photosensitized oxidation of d‐limonene (Malecha & Nizkorodov, 2017). It is therefore likely that aerosol particles containing naphthalene oxidation products (as well as oxidation products of PAHs in general) contribute to photosensitized chemistry in the atmosphere.…”

Syntheses of new chiral chimeric photo-organocatalysts

“… 18 Among them, ketones have a long history in photochemistry and, not only in pure organic synthesis, but also in environmental chemistry. 19 In particular, aryl ketones, such as benzophenone, 20 thioxanthone 18 a and anthraquinone 21 have long been appreciated for their long-lived triplet states and ability to act as effective photosensitizers in a wide number of photochemical transformations. Herein, we report the synthesis, the photophysical properties as well as some photocatalytic capabilities of these new chiral BINOL phosphoric acid photocatalysts bearing different photoactivable aromatic ketones at the 3 or 3,3′ positions.…”