Unfiltered Sunlight Research Articles

Bis-azopyrazole Photoswitches for Efficient Solar Light Harvesting.

Although natural sunlight is one of the most abundant and sustainable energy resources, only a fraction of its energy is currently harnessed and utilized in photoactive systems. The development of molecular photoswitches that can be directly activated by sunlight is imperative for unlocking the full potential of solar energy and addressing the growing energy demands. Herein, we designed a series of 2-amino-1,3-bis-azopyrazoles featuring a coupled πn system, resulting in a pronounced redshift in their spectral absorption, reaching up to 661 nm in the red region. By varying the amino substituents of these molecules, highly efficient E→Z photoisomerization under unfiltered sunlight can be achieved, with yields of up to 88.4 %. Moreover, the Z,Z-isomers have high thermal stability with half-lives from days to years at room temperature. The introduction of ortho-amino substitutions and meta-bisazo units leads to a reversal of the n-π* and πn-π* transitions on the energy scale. This change provides a new perspective for further tuning the visible absorption of azo-switches by utilizing the πn-π* band instead of the conventional n-π* band. These results suggest that photoresponsive systems can be powered by sunlight instead of traditional artificial lights, thereby paving the way for sustainable smart materials and devices.

Bis‐azopyrazole Photoswitches for Efficient Solar Light Harvesting

AbstractAlthough natural sunlight is one of the most abundant and sustainable energy resources, only a fraction of its energy is currently harnessed and utilized in photoactive systems. The development of molecular photoswitches that can be directly activated by sunlight is imperative for unlocking the full potential of solar energy and addressing the growing energy demands. Herein, we designed a series of 2‐amino‐1,3‐bis‐azopyrazoles featuring a coupled πn system, resulting in a pronounced redshift in their spectral absorption, reaching up to 661 nm in the red region. By varying the amino substituents of these molecules, highly efficient E→Z photoisomerization under unfiltered sunlight can be achieved, with yields of up to 88.4 %. Moreover, the Z,Z‐isomers have high thermal stability with half‐lives from days to years at room temperature. The introduction of ortho‐amino substitutions and meta‐bisazo units leads to a reversal of the n–π* and πn–π* transitions on the energy scale. This change provides a new perspective for further tuning the visible absorption of azo‐switches by utilizing the πn–π* band instead of the conventional n–π* band. These results suggest that photoresponsive systems can be powered by sunlight instead of traditional artificial lights, thereby paving the way for sustainable smart materials and devices.

Solar Azo-Switches for Effective E→Z Photoisomerization by Sunlight.

Natural photoactive systems have evolved to harness broad-spectrum light from solar radiation for critical functions such as light perception and photosynthetic energy conversion. Molecular photoswitches, which undergo structural changes upon light absorption, are artificial photoactive tools widely used for developing photoresponsive systems and converting light energy. However, photoswitches generally need to be activated by light of specific narrow wavelength ranges for effective photoconversion, which limits their ability to directly work under sunlight and to efficiently harvest solar energy. Here, focusing on azo-switches-the most extensively studied photoswitches, we demonstrate effective solar E→Z photoisomerization with photoconversions exceeding 80 % under unfiltered sunlight. These sunlight-driven azo-switches are developed by rendering the absorption of E isomers overwhelmingly stronger than that of Z isomers across a broad ultraviolet to visible spectrum. This unusual type of spectral profile is realized by a simple yet highly adjustable molecular design strategy, enabling the fine-tuning of spectral window that extends light absorption beyond 600 nm. Notably, back-photoconversion can be achieved without impairing the forward solar isomerization, resulting in unique light-reversible solar switches. Such exceptional solar chemistry of photoswitches provides unprecedented opportunities for developing sustainable light-driven systems and efficient solar energy technologies.

Solar Azo‐Switches for Effective E→Z Photoisomerization by Sunlight

AbstractNatural photoactive systems have evolved to harness broad‐spectrum light from solar radiation for critical functions such as light perception and photosynthetic energy conversion. Molecular photoswitches, which undergo structural changes upon light absorption, are artificial photoactive tools widely used for developing photoresponsive systems and converting light energy. However, photoswitches generally need to be activated by light of specific narrow wavelength ranges for effective photoconversion, which limits their ability to directly work under sunlight and to efficiently harvest solar energy. Here, focusing on azo‐switches—the most extensively studied photoswitches, we demonstrate effective solar E→Z photoisomerization with photoconversions exceeding 80 % under unfiltered sunlight. These sunlight‐driven azo‐switches are developed by rendering the absorption of E isomers overwhelmingly stronger than that of Z isomers across a broad ultraviolet to visible spectrum. This unusual type of spectral profile is realized by a simple yet highly adjustable molecular design strategy, enabling the fine‐tuning of spectral window that extends light absorption beyond 600 nm. Notably, back‐photoconversion can be achieved without impairing the forward solar isomerization, resulting in unique light‐reversible solar switches. Such exceptional solar chemistry of photoswitches provides unprecedented opportunities for developing sustainable light‐driven systems and efficient solar energy technologies.

Strong-bonding hole-transport layers reduce ultraviolet degradation of perovskite solar cells

The light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would receive in actual outdoor use. We report degradation mechanisms of p-i-n–structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) dominate the accelerated A-site cation migration, rather than direct degradation of HTMs. An aromatic phosphonic acid, [2-(9-ethyl-9H-carbazol-3-yl)ethyl]phosphonic acid (EtCz3EPA), enhanced bonding at the perovskite/HTM/TCO region with a phosphonic acid group bonded to TCOs and a nitrogen group interacting with lead in perovskites. A hybrid HTM of EtCz3EPA with strong hole-extraction polymers retained high efficiency and improved the UV stability of perovskite devices, and a champion perovskite minimodule—independently measured by the Perovskite PV Accelerator for Commercializing Technologies (PACT) center—retained operational efficiency of >16% after 29 weeks of outdoor testing.

Laser-type cooling with unfiltered sunlight.

Cooling of systems to sub-Kelvin temperatures is usually done using either a cold bath of particles or spontaneous photon scattering from a laser field; in either case, cooling is driven by interaction with a well-ordered cold (i.e., low-entropy) system. However, there have recently been several schemes proposed for "cooling by heating," in which raising the temperature of some mode drives the cooling of the desired system faster. We discuss how to cool a trapped ion to its motional ground state using unfiltered sunlight at 5800K to drive the cooling. We show how to treat the statistics of thermal light in a single-mode fiber for delivery to the ion and show experimentally how the blackbody spectrum is strongly modified by being embedded in quasi-one-dimension. Quantitative estimates for the achievable cooling rate with our measured fiber-coupled low-dimensional sunlight show promise for demonstrating this implementation of cooling by heating.

Abscisic acid modulates neighbor proximity-induced leaf hyponasty in Arabidopsis.

Leaves of shade-avoiding plants such as Arabidopsis (Arabidopsis thaliana) change their growth pattern and position in response to low red to far-red ratios (LRFRs) encountered in dense plant communities. Under LRFR, transcription factors of the phytochrome-interacting factor (PIF) family are derepressed. PIFs induce auxin production, which is required for promoting leaf hyponasty, thereby favoring access to unfiltered sunlight. Abscisic acid (ABA) has also been implicated in the control of leaf hyponasty, with gene expression patterns suggesting that LRFR regulates the ABA response. Here, we show that LRFR leads to a rapid increase in ABA levels in leaves. Changes in ABA levels depend on PIFs, which regulate the expression of genes encoding isoforms of the enzyme catalyzing a rate-limiting step in ABA biosynthesis. Interestingly, ABA biosynthesis and signaling mutants have more erect leaves than wild-type Arabidopsis under white light but respond less to LRFR. Consistent with this, ABA application decreases leaf angle under white light; however, this response is inhibited under LRFR. Tissue-specific interference with ABA signaling indicates that an ABA response is required in different cell types for LRFR-induced hyponasty. Collectively, our data indicate that LRFR triggers rapid PIF-mediated ABA production. ABA plays a different role in controlling hyponasty under white light than under LRFR. Moreover, ABA exerts its activity in multiple cell types to control leaf position.

Monochromatic light filters to enhance biomass and carotenoid productivities of Dunaliella salina in raceway ponds

Monochromatic blue and red wavelengths are more efficient for light to algal biomass conversion than full-spectrum sunlight. In this study, monochromatic light filters were used to down-regulate natural sunlight to blue (400–520 nm) and red (600–700 nm) wavelengths to enhance biomass productivity of Dunaliella salina in outdoor raceway ponds. Growth indices such as cell size, pigment concentrations, biomass yield, photosynthetic efficiency, and major nutritional compositions were determined and compared against a control receiving unfiltered sunlight. Results showed that red light increased biomass productivity, lipid, and carotenoid contents but decreased cell volume, chlorophyll production, and cell weight. Conversely, blue light increased cell volume by 200%, cell weight by 68%, and enhanced chlorophyll a and protein contents by 35% and 51%, respectively, over red light. Compared to the control treatment, photoinhibition of D. salina cells at noon sunshine was decreased 60% by utilizing optical filters on the pond’s surface.

Low Blue Light Enhances Phototropism by Releasing Cryptochrome1-Mediated Inhibition of PIF4 Expression.

Shade-avoiding plants, including Arabidopsis (Arabidopsis thaliana), display a number of growth responses, such as elongation of stem-like structures and repositioning of leaves, elicited by shade cues, including a reduction in the blue and red portions of the solar spectrum and a low-red to far-red ratio. Shade also promotes phototropism of de-etiolated seedlings through repression of phytochrome B, presumably to enhance capture of unfiltered sunlight. Here we show that both low blue light and a low-red to far-red light ratio are required to rapidly enhance phototropism in Arabidopsis seedlings. However, prolonged low blue light treatments are sufficient to promote phototropism through reduced cryptochrome1 (cry1) activation. The enhanced phototropic response of cry1 mutants in the lab and in response to natural canopies depends on PHYTOCHROME INTERACTING FACTORs (PIFs). In favorable light conditions, cry1 limits the expression of PIF4, while in low blue light, PIF4 expression increases, which contributes to phototropic enhancement. The analysis of quantitative DII-Venus, an auxin signaling reporter, indicates that low blue light leads to enhanced auxin signaling in the hypocotyl and, upon phototropic stimulation, a steeper auxin signaling gradient across the hypocotyl. We conclude that phototropic enhancement by canopy shade results from the combined activities of phytochrome B and cry1 that converge on PIF regulation.

Photocatalytic Performance of Zinc Ferrite Magnetic Nanostructures for Efficient Eriochrome Black-T Degradation from the Aqueous Environment under Unfiltered Sunlight

Herein, three different types of zinc ferrite (ZnFe2O4) magnetic nanoparticles as photocatalysts were synthesized from iron and zinc sulfate using a co-precipitation method. Tri ethylene glycol (TEG) was utilized as a capping/stabilizing agent in the presence of ammonium hydroxide. The as-prepared nanoparticles were annealed at 400 °C for 4 h followed by acid etching with HCl (for 15 min in I M solution). The thermally treated magnetic nanostructure was subjected to surface modification by treating with 3-aminopropyl (triethoxysilane) 3-(APTES) at 60 °C for 2 h. Various characterization techniques including Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET), and X-rays diffraction (XRD) were carried out to examine the structural properties of the pristine and functionalized nanocrystals. XRD pattern assessed the crystalline and nano size of the ZnFe2O4 recording particle sizes of 13.5, 23.3, and 106.5 nm for functionalized, annealed, and pristine ZnFe2O4 nanoparticles, respectively. FTIR spectral analysis corroborated the modifications and functionalization of the samples. BET analysis revealed a surface area of 0.6719 (functionalized), 45.21 (annealed), and 155.38 (pristine nanoparticles). The photocatalytic activity of the prepared nanostructures was investigated for Eriochrome Black T (EBT) dye under the unfiltered sunlight. At optimal reaction parameters, the photocatalytic rates of EBT dye for functionalized, annealed, and blank NP’s were 92, 91, and 83%, respectively. Kinetic models demonstrate that the degradation processes followed pseudo-first-order kinetics. The energies of the band gap in the acidic and basic media, as determined from the Tauc plot, were 2.47 and 2.7 eV, respectively. Taken together, the results showed that newly fabricated nanostructures are considered as promising photocatalysts in degrading organic pollutants for a sustainable environment.

Morphology and Flowering Responses of Four Bedding Plant Species to a Range of Red to Far Red Ratios

In greenhouse ornamental crop production, bedding plants grown below high densities of hanging baskets (HBs) tend to be of lower quality. Hanging basket crops can decrease the red to far red ratio (R:FR) of the growing environment below; however, the extent to which decreased R:FR affects plant morphology and flowering of the lower-level crops is unknown. The present study examined effects of R:FR on morphology and flowering of marigold ‘Antigua Orange’ (Tagetes erecta), petunia ‘Duvet Red’ (Petunia ×hybrida), calibrachoa ‘Kabloom Deep Blue’ (Calibrachoa ×hybrida), and geranium ‘Pinto Premium Salmon’ (Pelargonium ×hortorum). Five R:FR light treatments were provided ranging from R:FR 1.1 (representing unfiltered sunlight) to R:FR 0.7 (representing shaded conditions under HBs) using light-emitting diodes (LEDs) in growth chambers, each with identical photosynthetically active radiation (PAR) (400–700 nm) and FR added to achieve the target R:FR ratio. Two experiments using the same R:FR treatments were conducted with day/night temperature regimes of 20 °C/18 °C and 25 °C/21 °C, respectively. In the second experiment, a fluorescent light treatment was included. The results of the second experiment were more dramatic than the first, where reducing R:FR from 1.1 to 0.7 increased height by 11%, 22%, and 32% in marigold, petunia, and calibrachoa, respectively, and increased petiole length in geranium by 10%. Compared with R:FR 1.1, the R:FR 0.7 shortened the time to the appearance of first flower bud by 2 days in marigold, whereas flowering was minimally affected in other species. Compared with pooled data from the LED treatments, fluorescent light increased relative chlorophyll content for all species, reduced height in marigold, petunia, calibrachoa, and geranium by 26%, 67%, 60%, and 48%, and reduced stem dry weight by 28%, 39%, 21%, and 31%, respectively. The differences in morphology observed under fluorescent light compared with LED R:FR treatments indicate that light quality manipulation is a potential alternative to chemical growth regulators in controlled environments such as greenhouses and growth chambers.

Accelerated ageing of molybdenum oxide

The stability and lifetime of materials proposed for photovoltaic applications are important parameters, because such devices should offer long-term reliable performance whilst operating in a harsh environment. In this work, we present a powerful approach to accelerate and study the degradation mechanisms of molybdenum oxide, a material which has shown promise for next generation photovoltaics, and for enhanced hole extraction in organic photovoltaics. We use UV and soft x-rays to drive accelerated ageing, boosting the ageing time by a factor of up to 1000. Using this method, we find that molybdenum oxide does not offer reliable performance in environments in which heating or ionising radiation are present, because of its propensity to reduce, thus strongly modifying its electronic properties. We estimate that ≈100 d of unfiltered sunlight exposure would be sufficient to reduce this material into metallic MoO2. We also show that a very similar degradation can be driven by thermally, and that in both cases, the creation of oxygen vacancies is responsible. A lack of robustness to harsh operating conditions (i.e. UV and/or heat) brings the suitability of unprotected molybdenum oxide in photovoltaic applications into question.

Photo catalytic degradation of Alizarin red S using ZnS and cadmium doped ZnS nanoparticles under unfiltered sunlight

Zinc sulphide (ZnS) and cadmium doped ZnS (Cd-ZnS) nanoparticles were prepared by co-precipitation method and characterized by UV–Visible spectroscopy, X-ray diffraction (XRD) studies, Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). The optical band gaps of the synthesized materials were calculated from UV–Visible absorption spectra using Tauc plots. The band gap of ZnS was decreased from 3.4eV to 2.44eV due to substitution of Cd2+ ions in ZnS lattice at 0.5M cadmium content. This variation in the optical bandgap effectively monitored degradation of the dye. Photo catalytic degradation of Alizarin red S (ARS) by the nanoparticles showed that the cadmium doped ZnS acted as a potential photo catalyst under unfiltered natural sunlight of irradiation 300W/m2. The ARS dye was degraded about 50% and 96.7% in the presence of ZnS and Cd-ZnS (Cd 0.5M) nanoparticles respectively in 120min. Furthermore the effect of various parameters, i.e., photocatalyst concentration, dye concentration, and pH of the solution on the percentage of degradation was also studied. Degradation followed first order kinetics.

Characterization and role of tyrosinases in the lichenLobaria pulmonaria(L.) Hoffm.

AbstractTyrosinases are a widespread family of multicopper oxidase enzymes. In our earlier work, we identified the presence of tyrosinases in lichenized Ascomycetes based on their substratum specificity, sensitivity to inhibitors and molecular mass. Here, we present a more detailed characterization of a tyrosinase from the lichenLobaria pulmonaria. We also compare tyrosinase activity with the activities of laccases and peroxidases, the other redox enzymes present in this species. The importance of tyrosinases in lichen biology was studied by testing their role in melanin synthesis. Laboratory experiments clearly showed that tyrosinases fromL. pulmonariaresemble those from other lichens and in free-living fungi. While the tyrosinases can metabolize the melanin precursor L-DOPA, L-DOPA can also be metabolized by peroxidases and laccases. A field experiment showed that exposing shade-adaptedL. pulmonariato normal solar radiation induces L-DOPA melanin synthesis. Synthesis occurred when lichens were exposed to either direct sunlight, or placed under a wavelength-neutral filter that slightly reduced overall light. In lichens receiving unfiltered sunlight, melanin synthesis was accompanied by increased laccase activity; by contrast, no changes in enzyme activity occurred in lichens placed under the wavelength-neutral filter. Melanization was reduced by placing lichens under filters that removed UV-B, and prevented by filters that removed both UV-A and UV-B. Removing UV-B had no effect on enzyme activity, whereas removing both UV-A and UV-B increased tyrosinase activity. Results from this study indicate that under some conditions laccases may be involved in melanin synthesis, but they provide no evidence for a role for tyrosinases in melanization. Although high tyrosinase activities are widespread in lichens, many questions on the role of this enzyme in lichen biology remain to be answered.

Photochemical changes in water accommodated fractions of MC252 and surrogate oil created during solar exposure as determined by FT-ICR MS

To determine effects of photochemical weathering of petroleum, surrogate and Macondo (MC252) crude oils were exposed to solar radiation during the formation of Water Accommodated Fractions (WAFs) in sterile seawater. Samples were incubated in either unfiltered sunlight, with ultraviolet radiation blocked (Photosynthetically Active Radiation [PAR] only), or in darkness. WAFs were collected at two time points over the course of a week. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) analyses of water soluble species formed during exposure to sunlight were compared for the different treatments. Photochemical alterations resulted in differences in compound class distributions. In general, surrogate oil was photo-oxidized across a wider carbon number range compared to MC252. While photochemical differences were observed between MC252 and surrogate oils, microbial production in seawater responded similarly to both WAFs from both types of oils with the majority of the inhibition resulting from oil exposure to visible light.

Light intensity modulates the regulatory network of the shade avoidance response in Arabidopsis.

Plants such as Arabidopsis thaliana respond to foliar shade and neighbors who may become competitors for light resources by elongation growth to secure access to unfiltered sunlight. Challenges faced during this shade avoidance response (SAR) are different under a light-absorbing canopy and during neighbor detection where light remains abundant. In both situations, elongation growth depends on auxin and transcription factors of the phytochrome interacting factor (PIF) class. Using a computational modeling approach to study the SAR regulatory network, we identify and experimentally validate a previously unidentified role for long hypocotyl in far red 1, a negative regulator of the PIFs. Moreover, we find that during neighbor detection, growth is promoted primarily by the production of auxin. In contrast, in true shade, the system operates with less auxin but with an increased sensitivity to the hormonal signal. Our data suggest that this latter signal is less robust, which may reflect a cost-to-robustness tradeoff, a system trait long recognized by engineers and forming the basis of information theory.

On the dose dependency of the bleachable and non-bleachable components of IRSL from K-feldspar: Improved procedures for luminescence dating of Quaternary sediments

The infrared (IR) stimulated luminescence (IRSL) and post-IR IRSL (pIRIR) signals from K-feldspar can, for convenience, be divided into two components, bleachable and ‘non-bleachable’, where the latter corresponds to the ‘residual’ signal observed in sunlight-bleached samples. In this paper, we examine the non-bleachable component of IRSL of K-feldspar for several sedimentary samples from across Eurasia. We observed a large variability in the residual doses among these samples after prolonged exposure to sunlight. By employing multiple elevated temperature (MET) IR stimulations at 50–300 °C, we show that the residual dose increases systematically with stimulation temperature, attaining values as high as ∼50 Gy at 300 °C, even after several hours to tens of hours of exposure to unfiltered sunlight. We examined two samples in detail and found that the bleachable and non-bleachable components produced different dose response curves. Pulse annealing studies showed that the non-bleachable component is more stable than the bleachable component, suggesting that a preheat procedure cannot eliminate the non-bleachable component. Additional experiments revealed that the non-bleachable component is dose dependent. Owing to this dose dependency, we demonstrate mathematically and empirically that the simple subtraction of a residual dose from the measured equivalent dose (De) – which is the most common approach employed (if any residual dose is subtracted at all) – will result in underestimation of the actual De. We present a method to correct for the dose dependency of the residual dose, which can improve the accuracy of either MET-pIRIR or pIRIR age estimates for samples in which the non-bleachable component represents a significant fraction of the measured signals.

Experimental determination of photostability and fluorescence‐based detection of PAHs on the Martian surface

Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions.

Repression of shade‐avoidance reactions by sunfleck induction of HY5 expression in Arabidopsis

The light environment provides signals that play a critical role in the control of stem growth in plants. The reduced irradiance and altered spectral composition of shade light promote stem growth compared with unfiltered sunlight. However, whereas most studies have used seedlings exposed to contrasting but constant light treatments, the natural light environment may exhibit strong fluctuations. As a result of gaps in the canopy, plants shaded by neighbours may experience sunflecks, i.e., brief periods of exposure to unfiltered sunlight. Here, we show that sunflecks are perceived by phytochromes A and B, and inhibit hypocotyl growth in Arabidopsis thaliana mainly if they occur during the final portion of the photoperiod. By using forward and reverse genetic approaches we found that ELONGATED HYPOCOTYL 5, LATE ELONGATED HYPOCOTYL, PHYTOCHROME KINASE SUBSTRATE 4 and auxin signalling are key players in this response.

Stoichiometric dietary constraints influence the response of copepods to ultraviolet radiation‐induced oxidative stress

We carried out field experiments in two clear mountain lakes of both hemispheres (Lake Los Cántaros, Patagonia, Argentina, and Lake La Caldera, Sierra Nevada, Spain) performing a full factorial design (light × nutrients: unfiltered sun light (ultraviolet radiation treatment [UVR]) and screened sunlight (> 380 nm; photosynthetically active radiation treatment), with and without nutrient enrichment. We analyzed the direct effect of UVR on enzymatic antioxidant responses (catalase [CAT], glutathione S‐transferase [GST], and glutathione reductase [GR]) of two calanoid copepod species‐Boeckella gibbosa and Mixodiaptomus laciniatus‐ and the indirect effects of food quality (carbon : nutrient ratio) potentially affecting body elemental compositions and hence enzymatic activities. Responses for the three enzymes were different: GST increased its activity under UVR exposure in the two copepods, CAT activity was null and showed no response, and GR activity differed between species. Light treatments also affected sestonic elemental ratios; UVR exposure lowered carbon : phosphorus (C : P) ratios, which in turn affected the C: P elemental compositions of the copepods. However, nutrient addition had different effects on the two species; it did not affect final somatic C: P ratio of B. gibbosa but had a substantial effect on body elemental composition of M. laciniatus. Finally, the relationship between grazer’s C: P ratio and GST antioxidant enzyme activity was negative. UVR and nutrient inputs affected food quality, grazer somatic stoichiometry, and subsequently enzymatic responses. The ability of calanoid copepods to overcome increased UVR may depend, at least for GST, on the elemental nutrient balance of the food.