Heterogeneous Overhauser-DNP on 1 H dominated by scalar coupling in aqueous solution.

The Overhauser Dynamic Nuclear Polarization (O-DNP) of 1 H nuclei usually involves a dipolar coupling with the polarizing agent, whereas scalar coupling via hyperfine interactions are more common with 13 C nuclei. Here, we show a scalar-coupling dominated 1 H O-DNP, using polyaniline as a heterogeneous polarizing agent in an aqueous solution.

Blatter-type radicals as polarizing agents for electrochemical overhauser dynamic nuclear polarization.

Overhauser dynamic nuclear polarization (O-DNP) refers to a microwave-assisted process where an unpaired electron's (e.g. a radical) spin polarization is transferred to surrounding nuclei in solution, thus increasing the nuclear magnetic resonance (NMR) signal intensity of a given substance by several orders of magnitude. The presence of the unpaired electrons, which induces relaxation of the resulting hyperpolarized state when the radiation is halted, can be avoided by electrochemically removing the radicals on demand. We report the use of Blatter-type (benzo[e][1,2,4]triazinyl) radicals as polarizing agents, potentially opening the way to highly tunable radicals for electrochemical DNP.

Block Copolymer Stabilized Liquid Nanodroplets Facilitate Efficient Triplet Fusion-Based Photon Upconversion in Solid Polymer Matrices.

Sensitized triplet-triplet annihilation-based photon upconversion is a photophysical process that affords anti-Stokes-shifted emission after annihilation of two metastable triplet excitons of an emitter dye and the formation of a fluorescent singlet state. While this process readily occurs in solutions under conditions where the mobility of the dye molecules is high, particular architectures are required to facilitate efficient energy transfers in solid polymers. One possibility is to incorporate liquid upconverting domains into solid polymer matrices. Another possibility is to reduce the intermolecular distance between the dyes below the Dexter radius, allowing exciton migration via triplet hopping. We introduce herein nanostructured materials that combine both of these features. These glassy nanostructured polymer systems contain liquid upconverting nanodroplets that are stabilized with a block copolymer surfactant and are fabricated under ambient conditions in a facile one-step protocol. The dyes concentrate in the nanostructured liquid domains, and this enables hopping-mediated ET and TTA between the dyes and leads to an upconversion efficiency of ∼20%.

Nanodroplet-Containing Polymers for Efficient Low-Power Light Upconversion.

Sensitized triplet-triplet-annihilation-based photon upconversion (TTA-UC) permits the conversion of light into radiation of higher energy and involves a sequence of photophysical processes between two dyes. In contrast to other upconversion schemes, TTA-UC allows the frequency shifting of low-intensity light, which makes it particularly suitable for solar-energy harvesting technologies. High upconversion yields can be observed for low viscosity solutions of dyes; but, in solid materials, which are better suited for integration in devices, the process is usually less efficient. Here, it is shown that this problem can be solved by using transparent nanodroplet-containing polymers that consist of a continuous polymer matrix and a dispersed liquid phase containing the upconverting dyes. These materials can be accessed by a simple one-step procedure that involves the free-radical polymerization of a microemulsion of hydrophilic monomers, a lipophilic solvent, the upconverting dyes, and a surfactant. Several glassy and rubbery materials are explored and a range of dyes that enable TTA-UC in different spectral regions are utilized. The materials display upconversion efficiencies of up to ≈15%, approaching the performance of optimized oxygen-free reference solutions. The data suggest that the matrix not only serves as mechanically coherent carrier for the upconverting liquid phase, but also provides good protection from atmospheric oxygen.

Heterotetracenes: Flexible Synthesis and in Silico Assessment of the Hole-Transport Properties.

Thienoacenes and furoacenes are among the most frequent molecular units found in organic materials. The efficient synthesis of morphologically different heteroacenes and the rapid determination of their solid-state and electronic properties are still challenging tasks, which slow down progress in the development of new materials. Here, we report a flexible and efficient synthesis of unprecedented heterotetracenes based on a platinum- and gold-catalyzed cyclization-alkynylation domino process using EthynylBenziodoXole (EBX) hypervalent iodine reagents in the key step. The proof-of-principle in silico estimation of the synthesized tetracenes' charge transport properties reveals their strong dependence on both the position and nature of the heteroatoms in the ring system. A broad range of mobility is predicted, with some compounds displaying performance potentially comparable to that of state-of-the-art electronic organic materials.