Spotlights Cite This: J. Phys. Chem. Lett. 2018, 9, 1821−1821
pubs.acs.org/JPCL
Spotlights: Volume 9, Issue 7
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MAGNETICALLY INDUCED RING-CURRENT STRENGTHS IN MÖ BIUS TWISTED ANNULENES Every elementary school student can feel like a magician by half-twisting a strip of construction paper and securing the ends into a ring. Et voila: A two-sided strip of paper becomes onesided, and a Möbius band is created without the use of any magic at all. Molecules are sometimes twisted in the same way, and these, rather than paper rings, are the focus of a Letter by Wirz et al. (10.1021/acs.jpclett.8b00440). The authors note that, although aromaticity is an important concept in chemistry, and molecules with nonstandard topologies have attracted increasing interest, little is known about the effects of the spatial embedding of molecules with a given topology on their electric and magnetic properties. Using an annulene model system, they investigated the aromaticity or antiaromaticity of twisted and untwisted molecular ribbons by calculating the magnetically induced ring currents in six series of doubly charged and neutral structures. They found that the aromatic properties of the investigated Möbius twisted molecules depend not only on the linking number but also on the partitioning of the linking number into the twist and writhe contributions.
fitting parameter, so the measured charge generation yield can be compared across different material systems. The technique may advance our understanding of the charge-separation mechanism and allow for high-throughput screening of the charge generation yield of a variety of interfaces.
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WHAT CONTROLS THE LIMIT OF SUPERCOOLING AND SUPERHEATING OF PINNED ICE SURFACES? Nature has evolved a variety of antifreeze proteins and gylcoproteins that bind to ice and manage its growth and recrystallization in organisms that thrive at subfreezing temperatures. It has been proposed that these molecules pin the crystal surface, creating a curvature that arrests the growth and melting of the crystal. Using thermodynamic modeling and molecular simulations, Naullage et al. (10.1021/acs.jpclett.8b00300) demonstrate that the curvature of the superheated or supercooled surface depends on the temperature and distances between ice-binding molecules, but not the details of their interactions with ice. The authors’ simulations shed light on the nonequilibrium processes that lead to the irreversible growth or melting of pinned ice crystals. The authors elucidate the distinct role of the size of the ice-binding molecules on the melting and freezing hysteresis, thus explaining the asymmetry observed for these two properties in antifreeze proteins. The findings may aid in the development of efficient synthetic analogues of antifreeze proteins for use in cryopreservation.
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GRAPHENE FIELD-EFFECT TRANSISTOR AS A HIGH-THROUGHPUT PLATFORM TO PROBE CHARGE SEPARATION AT DONOR−ACCEPTOR INTERFACES In organic and low-dimensional materials, electrons and holes are bound together to form excitons. The separation of these two is called exciton dissociation, and it creates charge separation. Effective exciton dissociation at interfaces is essential for applications such as photovoltaics and photosensing, and the mechanism involved has attracted interest for years. Time-resolved optical spectroscopy is often used to study interfacial dynamics, but it is challenging to find a probe that is sensitive to the interfacial region because interfaces account for a small fraction of the total volume measured by the optical probe. Nonlinear spectroscopy techniques that are sensitive either to the interface or to the E-field produced by charge separation can be used to study the interfacial electron dynamics, but these methods involve complex setups and long measurement times. Data interpretation is not always straightforward, and often only a few selected model systems are studied by a particular technique because of the complexity. There is a need for a versatile and high-throughput method that can probe the charge-separation dynamics and yield a large number of material interfaces in a short period of time. Using the zinc phthalocyanine/fullerene interface, Kattel et al. (10.1021/acs.jpclett.8b00335) demonstrate a new method that uses the E-field sensitive nature of graphene to probe the E-field generated by the charge separation at donor− acceptor interfaces. The method has a short measurement time, high sensitivity, a simple experimental setup, and a universal data analysis procedure that can be applied to study charge separation at different material interfaces. The absolute number of separated carriers can be determined without the use of any © 2018 American Chemical Society
Published: April 5, 2018 1821
DOI: 10.1021/acs.jpclett.8b00936 J. Phys. Chem. Lett. 2018, 9, 1821−1821
