Quenching of meso-tetramethylpyridyl porphyrin excited triplet state by inorganic salts: Exciplex formation

Borissevitch, Iouri; Ferreira, Lúcia Pires; Gonçalves, Pablo José; Amado, André Miele; Schlothauer, Jan C.; Baptista, Maurı́cio S.

doi:10.1016/j.jphotochem.2018.08.020

Cited by 4 publications

(8 citation statements)

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“… 36 Alternately, anion-sensitizer exciplexes may also form and quench the excited singlet: the HA effect is thought to accelerate quenching via nonradiative dissipation of the energy. 18 In sum, the HA effect may play a role in the quenching of triplet excited sensitizers, but the improved FFA degradation in the fullerene case requires further elucidation.…”

Section: Resultsmentioning

confidence: 96%

“…Ionic species may impact the system in two ways: by altering 1 O 2 –FFA reaction rate constants 32 and by competitive exciplex formation between the 3 sens* and the ion (especially anions). 18 Rate constants for the 1 O 2 –FFA reaction in water were computed based on temperature (25 °C) and ion content, when possible, according to Appiani et al (2017); 32 these values are collated in Table 2 . Adding salt to RB reaction solutions improved apparent 1 O 2 yields in all cases except for NaI, which caused more than a 2-fold reduction in the rate of FFA loss.…”

Section: Resultsmentioning

confidence: 99%

“…Kinetic profiles for FFA degradation used to calculate these values are shown in Figure S4, along with FFA degradation in DMSO. Ionic species may impact the system in two ways: by altering 1 O 2 –FFA reaction rate constants and by competitive exciplex formation between the 3 sens* and the ion (especially anions) . Rate constants for the 1 O 2 –FFA reaction in water were computed based on temperature (25 °C) and ion content, when possible, according to Appiani et al (2017); these values are collated in Table .…”

Section: Resultsmentioning

confidence: 99%

“…Fullerenes, however, have innately efficient intersystem crossing (ISC) due to the curvature of their π–π bonding orbitals, so it is unclear to what extent the HA effect would increase the efficiency of 1 O 2 production from C 60 derivatives. Alternately, the HA effect may reduce the net 1 O 2 yield by accelerating nonradiative decay of a triplet states directly or of anion-sensitizer exciplexes, as demonstrated recently with a porphyrin-containing sensitizer …”

Section: Introductionmentioning

confidence: 89%

“…Alternately, the HA effect may reduce the net 1 O 2 yield by accelerating nonradiative decay of a triplet states directly 17 or of anion-sensitizer exciplexes, as demonstrated recently with a porphyrin-containing sensitizer. 18 …”

Section: Introductionmentioning

confidence: 99%

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The Overlooked Photochemistry of Iodine in Aqueous Suspensions of Fullerene Derivatives

et al. 2022

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Fullerene’s low water solubility was a serious challenge to researchers aiming to harness their excellent photochemical properties for aqueous applications. Cationic functionalization of the fullerene cage provided the most effective approach to increase water solubility, but common synthesis practices inadvertently complicated the photochemistry of these systems by introducing iodide as a counterion. This problem was overlooked until recent work noted a potentiation effect which occurred when photosensitizers were used to inactivate microorganisms with added potassium iodide. In this work, several photochemical pathways were explored to determine the extent and underlying mechanisms of iodide’s interference in the photosensitization of singlet oxygen by cationic fulleropyrrolidinium ions and rose bengal. Triplet excited state sensitizer lifetimes were measured via laser flash photolysis to probe the role of I – in triplet sensitizer quenching. Singlet oxygen production rates were compared across sensitizers in the presence or absence of I – , SO 4 2– , and other anions. 3,5-Dimethyl-1 H -pyrazole was employed as a chemical probe for iodine radical species, such as I·, but none were observed in the photochemical systems. Molecular iodine and triiodide, however, were found in significant quantities when photosensitizers were irradiated in the presence of I – and O 2 . The formation of I 2 in these photochemical systems calls into question the interpretations of prior studies that used I – as a counterion for photosensitizer materials. As an example, MS2 bacteriophages were inactivated here by cationic fullerenes with and without I – present, showing that I – moderately accelerated the MS2 deactivation, likely by producing I 2 . Production of I 2 did not appear to be directly correlated with estimates of 1 O 2 concentration, suggesting that the relevant photochemical pathways are more complex than direct reactions between 1 O 2 and I – in the bulk solution. On the basis of the results here, iodine photochemistry may be underappreciated and misunderstood in other environmental systems.

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Section: Resultsmentioning

confidence: 96%