Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 μJ cm–2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.

Photodegradation processes play an important role in releasing elements tied up in biologically refractory forms in the environment, and are increasingly recognized as important contributors to biogeochemical cycles. While complete photooxidation of dissolved organic carbon (to CO 2), and dissolved organic phosphorous (to PO 4 3-) has been documented, the analogous photoproduction of sulfate from dissolved organic sulfur (DOS) has not yet been reported. Recent high-resolution mass spectrometry studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter, which was hypothesized to result in the production of sulfate. Here, we provide evidence of ubiquitous production of sulfate, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA) during photodegradation of

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Photochemical reactions convert dissolved organic matter (DOM) into inorganic and low-molecular-weight organic products, contributing to its cycling across environmental compartments. However, knowledge on the formation mechanisms of these products is still scarce. In this work, we investigate the triplet-sensitized photodegradation of cysteine sulfinic acid, a (photo)degradation product of cysteine, to sulfate (SO 4 2− ). We use kinetic analysis, targeted experiments, and previous literature from several fields of chemistry to explain the elementary steps that lead to the release of sulfate. Our analysis indicates that triplet sensitizers act as oneelectron oxidants on the sulfinate S lone pair. The resulting radical undergoes C−S fragmentation to form SO 2 , which becomes hydrated to sulfite/bisulfite (S(IV)). S(IV) is further oxidized to SO 4 2− in the presence of triplet sensitizers and oxygen. We point out that the reaction sequence SO 2 ⇌ S(IV) → SO 4 2− is valid independently of the chemical structure of the model compound and might represent a sulfate photoproduction mechanism with general validity for DOS. Our mechanistic investigation revealed that amino acids in general might also be photochemical precursors of CO 2 , ammonia, acetaldehyde, and H 2 O 2 and that reaction byproducts can influence the rate and mechanism of S(IV) (photo)oxidation.

<p>In a recent study, we showed that photodegradation of dissolved organic sulfur (DOS) from a wide range of natural terrestrial environments releases sulfate (SO<sub>4</sub><sup>2–</sup>) and other small and highly oxidized S-containing compounds as degradation products, similar to what had already been reported for dissolved organic carbon, nitrogen and phosphorous. However, the underlying chemical mechanism of photoproduction of sulfate is still unknown.</p><p>To fill this knowledge gap, we selected cysteine as a DOS model compound and we investigated its photodegradation to sulfate using model sensitizers as the source of singlet oxygen (<sup>1</sup>O<sub>2</sub>) and triplet excited states (<sup>3</sup>Sens*), two photochemically produced reactive species ubiquitous in sunlit surface waters. Using a combination of steady-state photochemistry experiments, kinetic modeling and mechanistic knowledge from the biochemistry literature, we reconstructed the molecular events that likely lead to the release of sulfate. We found that the release of SO<sub>2</sub> via triplet-sensitized fragmentation of cysteine sulfinic acid, a <sup>1</sup>O<sub>2</sub> degradation product of cysteine, is a key step in the reaction mechanism. In the presence of oxygen and a photosensitizer, SO<sub>2</sub> is then rapidly oxidized to SO<sub>4</sub><sup>2–</sup>.</p><p>Interestingly, nowadays there is great interest in the atmospheric chemistry community on the same transformation (i.e., aqueous phase oxidation of SO<sub>2</sub> to SO<sub>4</sub><sup>2–</sup>) in the context of extreme haze events. Triplet-induced SO<sub>2</sub> oxidation has already been proposed as a potential aqueous phase reaction that might explain the mismatch between measured and modelled sulfate concentrations, but the mechanism of this process is still not established. Our work provides an example of how mechanistic knowledge gained on the (photo)chemical behaviour of dissolved organic matter in aquatic systems can offer insights on processes occurring in atmospheric aqueous phases.</p>

Despite its abundance, its importance in biological processes and its influence on metal bioavailability, the biogeochemical cycle of dissolved organic sulfur (DOS) in aquatic systems is still poorly understood. Recent high-resolution mass spectrometry studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter (DOM), which was hypothesized to be associated with the production of sulfate. Here we present evidence of ubiquitous production of sulfate and small non-volatile S-containing compounds during photodegradation of DOM samples from a wide range of natural environments. Our estimates indicate that photoproduction of sulfate in the ocean exceeds that of carbonyl sulfide and carbon disulfide by at least two orders of magnitude, suggesting that photodegradation plays a significant role in the aquatic and atmospheric cycle of DOS.<br>

<p>Despite its importance in biological processes and its influence on metal bioavailability, the biogeochemical cycle of dissolved organic sulfur (DOS) in aquatic systems is still poorly understood. Recent high-resolution mass spectrometry (HRMS) studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter (DOM), which was hypothesized to result in the production of sulfate. Here, we provide evidence of ubiquitous production of sulfate, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA) during photodegradation of DOM samples from a wide range of natural terrestrial environments. We show that photochemical production of sulfate is generally at least one order of magnitude more efficient than the production of MSA and MSIA, as well as volatile S-containing compounds (<i>i.e.</i>, CS₂and COS). We also identify possible molecular precursors for sulfate and MSA, and we demonstrate that a wide range of relevant classes of DOS compounds (in terms of S oxidation state and molecular structure) can liberate sulfate upon photosensitized degradation. This work indicates that photochemistry plays a more significant role in the aquatic and atmospheric cycle of DOS than currently believed.</p>