Infrared Spectra and Strain in Cyclic Carbonyl Compounds

Enhancing the Performance of Organic Solar Cells by Prolonging the Lifetime of Photogenerated Excitons

Exciton lifetime (τ) is crucial for the migration of excitons to donor/acceptor interfaces for subsequent charge separation in organic solar cells (OSCs); however, obvious prolongation of τ has rarely been achieved. Here, by introducing a solid additive 9-fluorenone-1-carboxylic acid (FCA) into the active layer, which comprises a nonfullerene acceptor, 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6/7-methyl)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IT-M), τ is substantially prolonged from 491 to 928 ps, together with obvious increases in fluorescence intensity and quantum yield. Time-resolved transient infrared spectra indicate the presence of an intermolecular vibrational coupling between the electronic excited state of IT-M and the electronic ground state of FCA, which is first observed here and which can suppress the internal conversion process. IT-M-based OSCs display an improved short-circuit current and fill factor after the addition of FCA. Thus, the power conversion efficiency is increased, particularly for devices with a large donor/acceptor ratio of 1:4, whose efficiency is increased by 56%. This study describes a novel method, which is also applicable to other nonfullerene acceptors, for further improving the performance of OSCs without affecting their morphology and light absorption properties.

Detailed characterization of Pinus ponderosa sporopollenin by infrared spectroscopy

In plant spores and pollen, sporopollenin occurs as a structural polymer with remarkable resistance to chemical degradation. This recalcitrant polymer is well-suited to analysis by non-destructive infrared spectroscopy. However, existing infrared characterization of sporopollenin has been limited in scope and occasionally contradictory. This study provides a comprehensive structural analysis of sporopollenin in the Pinus ponderosa pollen exine using infrared spectroscopy, including detailed band assignments, descriptions of chemical reactivity, and comparison to multiple reference substances. We observe that the infrared spectral characteristics of sporopollenin prepared by enzymatic digestion of the polysaccharide-based intine are largely consistent with a copolymer of aliphatic lipids and trans-4-hydroxycinnamic acid, without distinct contributions from α-pyrone or carotenoid substructures.

Functionalization of polyisoprene and polystyrene via reactive processing using azidoformate grafting agents, and its application to the synthesis of dioxaborolane-based polyisoprene vitrimers

Azidoformates carrying dioxaborolane functions were used to functionalize PI and PS, and to prepare PI vitrimers by reactive processing.

"Flex-activated" mechanophores: using polymer mechanochemistry to direct bond bending activation

We describe studies in mechanochemical transduction that probe the activation of bonds orthogonal to an elongated polymer main chain. Compression of mechanophore-cross-linked materials resulted in the release of small molecules via cleavage of covalent bonds that were not integral components of the elongated polymer segments. The reactivity is proposed to arise from the distribution of force through the cross-linking units of the polymer network and subsequent bond bending motions that are consistent with the geometric changes in the overall reaction. This departure from contemporary polymer mechanochemistry, in which activation is achieved primarily by force-induced bond elongation, is a first step toward mechanophores capable of releasing side-chain functionalities without inherently compromising the overall macromolecular architecture.

An expeditious synthesis of the MDM2-p53 inhibitor AM-8553

The development of the structurally complex MDM2/p53 inhibitor AM-8553 was impeded by the low yield of the initial synthesis. A second generation synthesis is described that features a Noyori dynamic kinetic resolution, a highly diastereoselective allylation, and a novel oxazoline-assisted piperidinone forming reaction to provide AM-8553 in 35.6% yield and 11 steps.

3-(2'-[18F]fluoroethyl)spiperone, a potent dopamine antagonist: synthesis, structural analysis and in-vivo utilization in humans

The synthesis of 3-(2'-[18F]fluoroethyl)spiperone (1c), a radiotracer useful for imaging the brain dopamine receptor system in vivo using positron emission tomography, is described. Precursors of 1c, the functional 3-N-alkyl derivatives of spiperone (4), were prepared by the alkylation of the amide group in spiperone (2a) by 1,2-disubstituted ethanes under phase transfer conditions. A comprehensive evaluation of the reaction of the derivatives 4a-h with no-carrier-added K18F/Kryptofix clearly indicated that the ketalized derivatives 4e-h were the choice of the precursors for 1c. The i.r., MS and NMR spectral data suggested that under phase transfer reaction conditions, the amide nitrogen was preferentially alkylated. To provide a firm basis for comparison with related analogues, an x-ray analysis was performed on a single crystal of 3-(2'-fluoroethyl)spiperone (1d). The tomographic behavior of 1c in human brain tissue was measured for more than 7 h and was consistent with the labeling of dopamine D-2 receptors.