Intermediate Photoproducts Research Articles

Effect of Cr cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures

In this work, we have investigated the effect of Cr3+ cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures. The Zn(1-(x-y))ErxCryO compound, where [(x; y) = (0.00; 0.00), (0.02; 0.01), (0.02; 0.02) and (0.02; 0.03)] was synthesized by the co-precipitation method and thermally treated at 100 °C for 6 h. The structural study showed that the dopant cations concentrations, cause variations in lattice constants, and increase the crystallite size and the strain in the ZnO crystal lattice. The structural atomic disorder was confirmed by Raman and photoluminescence spectroscopies, with VO, VO+, and VO++ type oxygen vacancy defects dominating. The samples exhibited different morphologies depending on the dopant concentration (plates-like, irregular hemispherical particles, and octahedrons-like structures). In the photocatalytic test, the methylene blue (MB) dye degradation under UV irradiation increased as a function of Cr3+ cations concentration, achieving a degradation rate of 37.4 ± 1.9% for the sample containing 2% of Er3+ cations and 3% of Cr3+ cations. In addition, the MB dye removal capacity by the Zn(1-(x-y))ErxCryO compound was incremented to above 85% using an optimized H2O2 concentration. Finally, the irradiated solution did not show toxicity against Artemia salina, indicating that the intermediate photoproducts formed are not toxic.

Impact of Reactive Oxygen Species Scavenging on the Intermediate Production of Anthracene and Anthraquinone in Fresh versus Saltwater Environments.

While salinity can alter the photodegradation of hydrophobic organic compounds (HOCs), the cause of their altered kinetics in seawater is not well understood. Because HOC intermediate photoproducts are often more toxic than their parent compounds, characterizing the generation of intermediates in saline environments is needed to accurately predict their health effects. The present study investigated the influence of salinity on the generation of anthraquinone through the photolysis of anthracene and the generation of anthrone and 1-hydroxyanthraquinone from the photolysis of anthraquinone as well as their reactivities with hydroxyl radicals. This was conducted by measuring the photolysis rates of anthracene and anthraquinone and characterizing their product formation in buffered deionized water, artificial seawater, individual seawater halides (bromide, chloride, and iodide), dimethyl sulfoxide, furfuryl alcohol, and solutions of hydrogen peroxide. Salinity enhanced the persistence of anthraquinone by a factor >10 and altered its product formation, including the generation of the suspected carcinogen 1-hydroxyanthraquinone. In part, this was attributed to reactive oxygen species (ROS) scavenging by the seawater constituents chloride and bromide. In addition, anthraquinone and its hydroxylated products were found to be moderately to highly reactive with hydroxyl radicals, further illustrating their tendency to react with ROS in aqueous environments. The present study emphasizes the importance of considering the effects of salinity on organic contaminant degradation; it can significantly enhance the persistence of HOCs and alter their intermediate formation, subsequently impacting chemical exposure times and potential toxic effects on estuarine/marine organisms. Environ Toxicol Chem 2023;42:1721-1729. © 2023 SETAC.

Visible Light‐fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals

AbstractIn the quest for essential energy solutions towards an ecological friendly future, the transformation of visible light/solar energy into mechanical motions in metal‐free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, and all‐organic electronic devices. Such green energy‐triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid‐base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both ultraviolet (UV) and visible light associated with quantitative single‐crystal‐to‐single‐crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light‐promoted dynamic green RTP as their emission peaks promptly blue‐shift, due to instantaneous photomechanical effects. Time‐dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X‐ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light‐driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli‐responsive multi‐functional crystalline materials.

Visible Light-fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals.

In the quest for essential energy solutions towards an ecological friendly future, the efficient transformation of visible light/solar energy into mechanical motions in metal-free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, sensing, and all-organic electronic devices. Such green energy-triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid-base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both UV and visible light associated with quantitative single-crystal-to-single-crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light-promoted dynamic green RTP as their emission peaks promptly blue-shift, due to instantaneous photomechanical effects. Time-dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X-ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light-driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli-responsive multi-functional crystalline materials.

Photomechanical Motions in Organoboron-Based Phosphorescent Molecular Crystals Driven by a Crystal-State [2 + 2] Cycloaddition Reaction.

Photoluminescent molecular crystals integrated with the ability to transform light energy into macroscopic mechanical motions are a promising choice of materials for both actuating and photonic devices. However, such dynamic photomechanical effects, based on molecular organoboron compounds as well as phosphorescent crystalline materials, are not yet known. Here we present an intriguing example of photomechanical molecular single crystals of a newly synthesized organoboron containing Lewis acid-base molecular adduct (BN1, substituted triphenylboroxine and 1,2-di(4-pyridyl)ethylene) having a capsule shape molecular geometry. The single crystals of BN1 under UV light exhibit controllable rapid bending-shape recovery, delamination, violent splitting-jumping, and expanding features. The detailed structural investigation by single-crystal X-ray diffraction and 1H NMR spectroscopy reveals that the photosalient behavior of the BN1 single crystals is driven by a crystal-to-crystal [2 + 2] cycloaddition reaction, supported by four donor-acceptor type B←N bonds. The instant photomechanical reaction in the BN1 crystals occurs under UV on account of sudden release of stress associated with the strained molecular geometry, significant solid-state molecular movements (supramolecular change), and cleavage of half intermolecular B←N linkages to result in a complete photodimerized single-crystalline product via the existence of two other intermediate photoproducts. In addition, the BN1 crystals display short-lived room temperature phosphorescence, and the photodynamic events are accompanied by the enhancement of their phosphorescence intensity to yield the photoproduct. Interestingly, the molecular crystals of the final photoproduct polymerize at ambient conditions when recrystallized from the solution forming a 2D supramolecular crystalline polymer stabilized by the retention of all B←N coordination modes.

Improved Photocatalyzed Degradation of Phenol, as a Model Pollutant, over Metal-Impregnated Nanosized TiO2.

Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO2 (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO2-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO2-P25 lattice induces tensile strain in Cu-impregnated TiO2-P25, whereas compressive strain in Cr- and V-impregnated TiO2-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N2 adsorption–desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC–UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO2-P25, the reactivity order being Cu > V >> Cr > TiO2-P25 under 366 nm irradiation, while TiO2-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC–MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.

Development of a new recyclable nanocomoposite LDH-TiO2 for the degradation of antibiotic sulfamethoxazole under UVA radiation: An approach towards sunlight

The aim of this study is the development of a new photocatalyst based on a calcined layered double hydroxide impregnated by TiO2 for the degradation of antibiotic sulfamethoxazole under UVA radiation. The most used catalyst TiO2-P25 has a high photocatalytic activity, but the difficulty of its elimination and regeneration remains a major drawback. To solve this problem, we have developed the nanocomposite LDH-TiO2 to study its performance and recycling possibility in order to reduce the contamination of water with drugs, which are a threat to public health and water resource quality. The massive use of antibiotics reveals their release in nature, which causes toxicity to aquatic organisms and thus develops a resistance of aquatic bacteria to these products. After the catalytic process carried out by hydroxyl radicals, six intermediate photoproducts were detected and subsequently their total mineralization was confirmed after COD analysis. The regeneration study of the catalyst LDH-TiO2 shows that it has excellent recyclability.

Photodegradation mechanisms of acyclovir in water and the toxicity of photoproducts

Acyclovir (ACV), an anti-virus drug, was widely detected in natural water at concentrations ranging from ng L−1 to μg L−1 due to inefficient biological treatments in sewage treatment plant. Photochemical experiments involving the irradiation from a xenon lamp simulating sunlight were conducted to explore the environmental behavior and potential risks of ACV. Isopropanol was used as a radical trapping agent for mechanism research, and the toxicity of the photoproducts of ACV was evaluated by the acute toxicity test of Photobacterium phosphoreum T3 spp. The results indicated that the ACV photodegradation followed pseudo first-order reaction kinetics, and the ACV removal rate increased when the pH was elevated from 5 to 10. The photochemical reaction pathway revealed by HPLC–MS/MS suggested that the C–C bond and C–N bond of ACV could be attacked by ·OH; thus, the photoproducts were mostly composed of hydroxyl substitution products. The intermediate photoproducts in the course of photodegradation exhibited a higher toxicity than the parent ACV, and the highest toxicity effect was observed at 6 h, which implied that the photoproducts of ACV might pose a great potential risk on aquatic environments.

Photo-oxidation kinetics of sugars having different molecular size and glycosidic linkages for their complete mineralization to subunits by bare/Ag–TiO 2 under UV irradiation

Abstract Food industries discharge a large quantity of waste water effluent containing a variety of water-soluble carbohydrates which differ with regard to structural moiety and molecular mass. These carbohydrates, although non-toxic could serve as nutrients for the growth of many harmful microorganisms that cause various diseases of humans and aquatic life forms. Therefore, the soluble sugars need to be removed from the waste water prior to disposal to the environment. This research demonstrates the comparative photodegradation kinetics of monosaccharide, disaccharide, and polysaccharides by bare and Ag–TiO2 depending upon their molecular weight and glycosidic linkages under UV irradiation. It revealed that Ag loading onto TiO2 notably improved the photo-oxidation rates of sugar molecules to different hydroxylated intermediate photoproducts that ultimately decomposed to CO2. Plausible degradation kinetics and mechanistic pathways for complete photomineralization of these sugars to CO2 are briefly illustrated here by measuring optical rotation using polarimeter along with HPLC, GC and LC-MS analyses.

The contribution of indirect photolysis to the degradation of graphene oxide in sunlight

This paper probes the role of hydroxyl radicals (·OH) generated by H2O2 photolysis on graphene oxide (GO) phototransformation, under simulated sunlight. It focuses on comparing the photoreaction of GO with (indirect) and without (direct) added H2O2 under simulated sunlight conditions. The biomarker responses of fish epithelial cells in in vitro assays of parent GO and GO photoreacted with H2O2 and their interaction with model biomembranes are also compared. GO was found to be far more extensively photodecomposed in the presence of H2O2, with ∼85% of the initial carbon content converted to CO2 during 48 h of irradiation. Direct and indirect photoreactions occurred concurrently in GO samples containing H2O2, and indirect photoreaction accounted for ∼70% of GO conversion to CO2. Reaction with ·OH causes increases in the concentrations of carboxylic acid groups of photoreacted GO and low-molecular-weight (LMW) species as part of the intermediate photoproducts. Compared to parent GO, intermediate photoproducts exhibited reduced interaction with model cell membranes and altered biomarker responses. Kinetic analysis extrapolating our data to conditions prevalent in sunlit surface waters predicts that initial GO photoreaction is dominated by direct photolysis, while indirect photoreactions involving ·OH determine subsequent conversion of intermediate GO photoproducts to CO2.

Photochemical reactivity of aqueous fullerene clusters: C60 versus C70

Over the past few years, there has been a strong interest in exploring the potential impact of fullerenes in the environment. Despite that both C60 and C70 have been detected in environmental matrices, the research on the impact of higher fullerenes, such as C70, has been largely missing. This study evaluated and compared the phototransformation of aqueous C60 and C70 clusters (nC60 and nC70) and their 1O2 production under sunlight and lamp light irradiation (315nm, 360nm and 420nm). The nC60 and nC70 samples formed by direct mixing with water adopted a face-centered cubic (FCC) crystal structure. The apparent quantum yields (AQYs) of fullerene phototransformed were relatively constant over the examined wavelengths, while 1O2 production AQYs decreased with increased wavelengths. The long-term fate studies with outdoor sunlight indicated that both nC60 and nC70 lost considerable organic carbon contents (>80%) in water after ∼8 months of irradiation and that the intermediate photoproducts of nC60 and nC70 exhibited a progressively increased level of oxygen-containing functionalities. Overall, the study indicates that nC70 can be photochemically removed under sunlight conditions and that the photoreactivity of nC60 based on AQYs is greater than that of nC70.

Solvent effect on the photo-induced proton transfer in 2-(N-methyl-α-iminoethyl)-phenol

Effects caused by water environment on the photo-induced proton transfer in 2-(N-methyl-α-iminoethyl)-phenol molecule are investigated by means of quantum chemical calculations. After the electronic excitation, the protonated Schiff base is twisted out from the molecular plane and later reverts to the initial state. Two possible energy relaxation pathways are revealed: photon emission from the excited-state minimum, and the non-radiative conversion through the conical intersection. Accounting for the local solvent interactions introduces substantial changes of the ground- and excited-state potential energy surfaces. These changes offer an explanation for the observed formation of the intermediate photoproducts of aromatic anils in polar solvents.

Bleaching of mouse rods: microspectrophotometry and suction‐electrode recording

When a substantial fraction of rhodopsin in a rod photoreceptor is exposed to bright light, the rod is desensitized by a process known as bleaching adaptation. Experiments on isolated photoreceptors in amphibians have revealed many of the features of bleaching adaptation, but such experiments have not so far been possible in mammals. We now describe a method for making microspectrophotometric measurements of pigment concentration and suction-electrode recording of electrical responses over a wide range of bleaching exposures from isolated mouse rods or pieces of mouse retina. We show that if pigment is bleached at a low rate in the presence of bovine serum albumin (BSA), and intermediate photoproducts are allowed to decay, mouse rods are stably desensitized; subsequent treatment with exogenous 11-cis retinal results in pigment regeneration and substantial recovery of sensitivity to the dark-adapted value. Stably bleached wild-type (WT) rods show a decrease in circulating current and acceleration of the time course of decay, much as in steady background light; similar effects are seen in guanylyl cyclase-activating protein knockout (GCAPs(-/-)) rods, indicating that regulation of guanylyl cyclase is not necessary for at least a part of the adaptation produced by bleaching. Our experiments demonstrate that in mammalian rods, as in amphibian rods, steady-state desensitization after bleaching is produced by two components: (1) a reduction in the probability of photon absorption produced by a decrease in rhodopsin concentration; and (2) an equivalent background light whose intensity is proportional to the fraction of bleached pigment, and which adapts the rod like real background light. These two mechanisms together fully account for the ‘log-linear' relationship in mammalian retina between sensitivity and per cent bleach, which can be measured in the steady state following exposure to bright light. Our methods will now make possible an examination of bleaching adaptation and pigment regeneration in mouse animal lines with mutations or other alterations in the proteins of transduction.

Removal of amoxicillin by UV and UV/H2O2 processes

The degradation of the β-lactam antibiotic amoxicillin (AM) treated with direct UV-C and UV/H2O2 photolytic processes was investigated in the present study. In addition, the antibacterial activity of the solution treated by UV/H2O2 advanced oxidation was compared with AM solution treated with ozone. The degradation rate of amoxicillin in both processes fitted pseudo first-order kinetics, and the rates increased up to six fold with increasing H2O2 addition at 10mM H2O2 compared to direct photolysis. However, low mineralization was achieved in both processes, showing a maximum of 50% TOC removal with UV/H2O2 after a reaction time of 80min (UV dose: 3.8×10−3EinsteinL−1) with the addition of 10mM H2O2. The transformation products formed during the degradation of amoxicillin in the UV and UV/H2O2 processes were identified by LC-IT-TOF analysis. In addition, microbial growth inhibition bioassays were performed to determine any residual antibacterial activity from potential photoproducts remaining in the treated solutions. An increase of the antibacterial activity in the UV/H2O2 treated samples was observed compared to the untreated sample in a time-based comparison. However, the UV/H2O2 process effectively eliminated any antibacterial activity from AM and its intermediate photoproducts at 20min of contact time with a 10mM H2O2 dose after the complete elimination of AM, even though the UV/H2O2 advanced oxidation process led to bioactive photoproducts.

PHOTOCATALYTIC DEGRADATION OF PATENT BLUE V BY SUPPORTED TiO2: KINETICS, MINERALIZATION, AND REACTION PATHWAY

The photocatalytic degradation of patent blue V (sodium salt of [4-(α-(4-diethylaminophenyl)-5-hydroxy-2, 4-disulfophenyl-methylidene)-2, 5-cyclohexadien-1-ylidene] diethylammonium hydroxide) in aqueous solutions has been investigated by using TiO2-coated nonwoven fibers as the photocatalyst. Before the study began, adsorption in the dark was done, and the effect of the initial concentration of dye in the solution was determined. The mineralization was monitored by chemical oxygen demand (COD), and the HPLC-MS method was used to identify reaction intermediates. The experimental results show that adsorption is an important parameter, controlling the apparent kinetic constant of degradation. The rate of fading was favored by a high concentration of dye in the solution with respect to the Langmuir-Hinshelwood model. The COD abatement was slower than the discoloration of the solution; this indicates that the dye was not directly mineralized, but transformed to intermediate photoproducts. These intermediate photoproducts lead to other cycles of degradation, to the point of total mineralization. Several by-products were detected and identified by HPLC-MS. On the basis of these findings, we propose a probable degradation pathway as critical for assessing the suitability of detoxification procedures for the degradation of particular contaminant classes.

Photo-removal of sulfamethoxazole (SMX) by photolytic and photocatalytic processes in a batch reactor under UV-C radiation (λmax = 254 nm)

In this study, photolytic and photocatalytic removal of the antibiotic sulfamethoxazole (SMX) under UVC radiation (λ=254nm) was investigated. The light intensity distribution inside the batch photoreactor was characterized by azoxybenzene actinometry. The intensity of incident radiation was found to be a strong function of position inside the reactor. 12mgL−1 of SMX was completely removed within 10min of irradiation under UVC photolysis, compared to 30min under TiO2 photocatalysis. COD measurement was used as an indication of the mineralization efficiency of both processes and higher COD removal with photocatalysis was shown. After 6h of reaction with photolysis and photocatalysis, 24% and 87% removal of COD was observed, respectively. Two of the intermediate photo-products were identified as sulfanilic acid and 3-amino-5-methylisoxazole by direct comparison of the HPLC chromatograms of standards to those of treated solutions. Ecotoxicity of treated and untreated solutions of SMX towards Daphnia magna was also investigated. It was found that a 3:1 ratio of sample to standard freshwater and a high initial concentration of 60mgL−1 of SMX were used to obtain reliable and reproducible results. The photo-products formed during photocatalytic and photolytic processes were shown to be generally more toxic than the parent compound.

Photosensitized reduction of water to hydrogen using novel Maya blue-like organic–inorganic hybrid material

On the basis of the understanding that membranes play an important role in the separation of the intermediate photoproducts in the photosynthetic process, a novel efficient hydrogen evolution system was constructed with Maya blue-like organic–inorganic hybrid material as a photocatalyst, in which palygorskite acts as matrix and Eosin Y as a photosensitizer. Under visible light irradiation ( λ ⩾ 420 nm ), the highest rate of hydrogen evolution and apparent quantum yield are about 3247.2 μmol h −1 (g Eosin Y) −1 and 12.5%, respectively. Negatively charged palygorskite particles could control the photosensitized electron-transfer reaction by means of electrostatic interaction. Based on the activities of hydrogen generation and the experimental measurements of UV–vis absorbance and fluorescence, a probable mechanism for photosensitized hydrogen evolution was postulated.

A Photochemical Mechanism for Homochirogenesis

Theoretical analysis of one-step and multiple-step photoreactions initiated with circularly polarized light shows that the enantiomeric excess of a chiral reactant approaches +/- 1 as the amount of unreacted reactant approaches 0. The final product never has a large enantiomeric excess at any stage of its formation and slowly decreases to 0 at the completion of the reaction. For multiple-step reactions the behavior of the intermediate photoproducts is much more interesting. During certain stages of the overall reaction both the size of the enantiomer excess and the amount of a given intermediate photoproduct are large. Furthermore, the sign of the enantiomeric excess of an intermediate may change during the course of the reaction. Multiple-step photoreactions initiated with circularly polarized light may be a method by which the exogenous and endogenous synthesis of optically active molecules occurred in the prebiotic universe.

Effect of natural aquatic humic substances on the photodegradation of bisphenol A

The photochemical degradation of bisphenol A (BPA) was studied in the presence of natural humic substances from different origins under simulated solar irradiation. BPA underwent insignificant direct photolysis in neutral water, but rapid photosensitized degradation in four humic substances solutions via pseudo-first-order reaction occurred. The photo-degradation rate of BPA was insensitive to the different initial BPA concentrations and was inhibited in aerated solution compared with the deoxygenated medium. The reactive oxygen species (ROS) such as ·OH and 1O2 produced from excitation of humic substances under irradiation was determined from the quenching kinetic experiment using molecular probe. The five main intermediate photoproducts of BPA in Nordic lake fulvic acid (NOFA) were tentatively identified using gas chromatography/mass spectrometer (GC/MS). Based on the identification of ROS and the analysis of photoproduct formation, the possible phototransformation pathways of BPA were proposed, involving the direct photolysis due to the energy transfer from the triplet state humic substance (3HS*) to BPA molecules and hydroxyl radical addition and oxidation as well.

Photo-degradation of bacteriochlorophyll c in intact cells and extracts from Chlorobium tepidum

The photo-stability of bacteriochlorophyll c (Bchlc) in an acetone–methanol–water solution extracted from Chlorobium tepidum and in the chlorosomes of intact Chlorobium tepidum cells is studied. The photo-stability of Bchlc in the chlorosomes is high (quantum yield of photo-degradation φ D≈8×10 −7). In air-saturated acetone–methanol–water solution the photo-degradation of Bchlc is caused by chemical reaction with the dissolved oxygen, where triplet Bchlc produces singlet oxygen, and singlet oxygen reacts with Bchlc to form stable oxidized linear tetrapyrroles as well as intermediate oxidized bacteriochlorophylls. The intermediate photoproducts degrade to linear tetrapyrroles by the catalytic action of triplet oxygen. The initial quantum yield of photo-degradation is direct proportional to the concentration of Bchlc giving φ D,0≈0.011 for a 7×10 −6 M solution at an excitation wavelength of 672 nm. In nitrogen-bubbled solution the photo-degradation is dominated by direct photoproduct formation in the triplet state of Bchlc. Long-wavelength absorbing intermediate photoproducts degrade slowly in the dark to short-wavelength absorbing stable photoproducts. The quantum yield of photo-degradation of a de-oxygenated solution was found to be φ D,0≈0.0012 for excitation at 672 nm.