The dielectric constant (εr) of organic semiconductors is a key material parameter for improving device performance in the field of organic electronics. However, the effect of the dielectric constant on the electronic and optoelectronic properties of materials remains unclear due to the scarcity of known organic semiconductors with an εr value higher than 6. Herein, the optical and electronic properties of a homologous series of fullerene derivatives with high εr are studied. The low frequency (<106 Hz) εr is extracted from the capacitance measured using impedance spectroscopy, and the effect of length (n) and geometrical arrangement of the polar ethylene glycol (EG) side chains is investigated. The εr is found to correlate with length for the symmetrical Bingel adducts, whereas for the unsymmetrical branched-EG chain adducts there is no significant difference between the two EG chain lengths. For BTrEG-2, the εr reaches 10, which is an unprecedented value in monoadduct fullerene derivatives. These materials open up new possibilities of studying the effect of εr in organic electronic devices such as organic photovoltaics, organic thermoelectrics, and organic field-effect transistors.
Blooms of pigmented algae darken the surface of glaciers and ice sheets, thereby enhancing solar energy absorption and amplifying ice and snow melt. The impacts of algal pigment and community composition on surface darkening are still poorly understood. Here, we characterise glacier ice and snow algal pigment signatures on snow and bare ice surfaces and study their role in photophysiology and energy absorption on three glaciers in Southeast Greenland. Purpurogallin and astaxanthin esters dominated the glacier ice and snow algal pigment pools (mass ratios to chlorophyll a of 32 and 56, respectively). Algal biomass and pigments impacted chromophoric dissolved organic matter concentrations. Despite the effective absorption of astaxanthin esters at wavelengths where incoming irradiance peaks, the cellular energy absorption of snow algae was 95% lower than anticipated from their pigmentation, due to pigment packaging. The energy absorption of glacier ice algae was consequently ~ 5 × higher. On bare ice, snow algae may have locally contributed up to 13% to total biological radiative forcing, despite contributing 44% to total biomass. Our results give new insights into the impact of algal community composition on bare ice energy absorption and biomass accumulation during snow melt.
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<p>Large blooms of purple-brownish pigmented glacier algae cover the ablation zones of the Greenland Ice Sheet (GrIS) and amplify its melt by lowering the ice surface albedo and increasing its solar radiation absorption. The darkening effect of these Zygnematophycean algae can be mainly attributed to their phenolic pigments, which absorb in the visible (VIS) and UV light ranges. Currently, a mechanistic understanding of the factors regulating the production of these pigments and their implications for the large-scale biologically-driven albedo reduction on the GrIS is missing. Here, we reveal how light (VIS vs. UV range) controls the phenolic pigment production, endo- and exometabolome, gene expression and photosynthetic performance of glacier algae. Two different algal communities (a mixed natural microbial community collected from snow-free ice and a laboratory-grown community of the ice algae <em>Mesotaenium berggrenii</em> without its original dark pigmentation) were used for a set of <em>in situ</em> incubations on Mittivakkat glacier in SE-Greenland. Pulse-amplitude-modulated (PAM) fluorometry revealed an overall higher photosynthetic performance (electron transport rate) at higher irradiances for the field population containing purpurogallin-like pigments compared to the lab community without dark pigmentation. The lab population showed a low maximum quantum efficiency of photosystem II under in situ light conditions, indicating a photo-damaging effect from high intensities of UV light in the absence of purpurogallin-derived phenolic pigments. Our study highlights the intracellular shading effect by purpurogallin-derived pigments, which are key for the survival of glacier algae on the ice and forms a cornerstone of understanding the large-scale variability in the biological darkening of the GrIS.</p>
Volatile organic compounds (VOCs) are emitted by organisms for a range of physiological and ecological reasons. They play an important role in biosphere–atmosphere interactions and contribute to the formation of atmospheric secondary aerosols. The Greenland ice sheet is home to a variety of microbial communities, including highly abundant glacier ice algae, yet nothing is known about the VOCs emitted by glacial communities. For the first time, we present VOC emissions from supraglacial habitats colonized by active microbial communities on the southern Greenland ice sheet during July 2020. Emissions of C5–C30 compounds from bare ice, cryoconite holes, and red snow were collected using a push–pull chamber active sampling system. A total of 92 compounds were detected, yielding mean total VOC emission rates of 3.97 ± 0.70 μg m–2 h–1 from bare ice surfaces (n = 31), 1.63 ± 0.13 μg m–2 h–1 from cryoconite holes (n = 4), and 0.92 ± 0.08 μg m–2 h–1 from red snow (n = 2). No correlations were found between VOC emissions and ice surface algal counts, but a weak positive correlation (r = 0.43, p = 0.015, n = 31) between VOC emission rates from bare ice surfaces and incoming shortwave radiation was found. We propose that this may be due to the stress that high solar irradiance causes in bare ice microbial communities. Acetophenone, benzaldehyde, and phenylmaleic anhydride, all of which have reported antifungal activity, accounted for 51.1 ± 11.7% of emissions from bare ice surfaces, indicating a potential defense strategy against fungal infections. Greenland ice sheet microbial habitats are, hence, potential sources of VOCs that may play a role in supraglacial microbial interactions, as well as local atmospheric chemistry, and merit future research efforts.
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