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Abstract: Propazine (2-chloro-4,6-diisopropylamino-1,3,5-triazine) is a triazine herbicide used to control broadleaf weeds and annual grasses during the production of milo grain sorghum. This compound provides post-emergent protection by interfering with photosynthetic electron transport of target weeds. Tolerant crops are able to degrade the applied herbicide to nontoxic metabolites. Propazine is electrochemically active under acidic conditions. Electrochemical reduction pathways for this herbicide have been proposed based on differential pulse polarography (DPP) studies. Theoretical deconvolutions of the experimental polarograms were consistent with a 2-electron cleavage of the C–Cl bond via a mechanism involving a protonation step in between the two electron transfers. The resulting intermediate was then reduced by an irreversible 2-electron reduction of the ring to produce the final product. We report supporting nuclear magnetic resonance (NMR) evidence for the electrochemical dechlorination of propazine and reduction of the triazine ring using controlled potential electrolysis (CPE) and a mercury pool electrode under acidic conditions. [Copyright &y& Elsevier]

Thesynthesis of dioxolane-functionalized hexacenes and heptacenesis reported. While heptacenes were too reactive to be successfullyisolated, hexacenes showed higher stability and characteristic long-wavelengthfluorescence both in solution and in the solid state as crystallinepowders. [ABSTRACT FROM AUTHOR]

Abstract: Over the last decade, researchers have investigated the electrochemical reduction pathways of a popular triazine herbicide known as atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) using controlled potential electrolysis and a mercury pool electrode. There is general agreement that a two-electron dechlorination process is a likely reduction pathway. However, Faraday’s law calculations indicated an overall four-electron reduction process. Additional pathways including the elimination of the ethyl group, elimination of the ethylamino group, and reduction of the triazine ring have been proposed. We believe to have NMR evidence for the reduction of the triazine ring using controlled potential electrolysis and a mercury pool electrode. We would like to add our results to the ongoing studies of this important triazine herbicide. [Copyright &y& Elsevier]

Approaches to control the self‐assembly of aromatic structures to enhance intermolecular electronic coupling are the key to the development of new electronic and photonic materials. Acenes in particular have proven simple to functionalize to induce strong π‐stacking interactions, although finer control of intermolecular π‐overlap has proven more difficult to accomplish. In this report, we describe how very weak hydrogen bonding interactions can exert profound impact on solid‐state order in solubilized pentacenes, inducing self‐assembly in either head‐to‐tail motifs with strong 2‐D π‐stacking, or head‐to‐head orientations with much weaker, 1‐D π‐stacking arrangements. In order to achieve 3‐D π‐stacking useful for photovoltaic applications, we elaborated a series of diethynyl pentacenes to their trimeric dehydro[18]annulene forms. These large, strongly interacting structures did indeed behave as acceptors in polymer photovoltaic devices. [ABSTRACT FROM AUTHOR]

Through a close examination of the intermolecular interactions of rubrene (1a) and select derivatives (1b-1p), a clearer understanding of why certain fluorinated rubrene derivatives pack with planar tetracene backbones has been achieved. In this study we synthesized, crystallized, and determined the packing structure of new rubrene derivatives (1h-p). Previously, we proposed that introducing electron-withdrawing CF3 substituents induced planarity by reducing intramolecular repulsion between the peripheral aryl groups (1e-g). However, we found that in most cases, further increasing the fluorine content of rubrene lead to twisted tetracene backbones in the solid state. To understand how rubrene (1a) and its derivatives (1b-p) pack in the solid state, we (re)examined the crystal structures through a systematic study of the close contacts. We found that planar tetracene cores occur when close contacts organize to produce an S symmetry element about a given rubrene molecule. We report the first instance of rubrene derivatives (1l and 1n) that pack in a two-dimensional brick motif. The prospects for new rubrene derivatives in semiconductors were estimated by calculating the reorganization energies of the monomers and transfer integrals of the dimers we observed. Our work allows for the rational design and improved crystal engineering of new rubrene derivatives. [ABSTRACT FROM AUTHOR]

Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spinsinglet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]-- tetracene we find rapid (<100 ps) formation of excimers and a slower (~10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process. [ABSTRACT FROM AUTHOR]

We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV. [ABSTRACT FROM AUTHOR]

Microfluidic approaches for controlled generation ofcolloidalclusters, for example, via encapsulation of colloidal particles indroplets, have been used for the synthesis of functional materialsincluding drug delivery carriers. Most of the studies, however, usea low concentration of an original colloidal suspension (<10 wt%). Here we demonstrate microfluidic approaches for directly makingdroplets with moderate (10–25 wt %) and high (>60 wt %)particleconcentrations. Three types of microfluidic devices, PDMS flow-focusing,PDMS T-junction, and microcapillary devices, are investigated fordirect encapsulation of a high concentration of polystyrene (PS) nanoparticlesin droplets. In particular, it is shown that PDMS devices fabricatedby soft lithography can generate droplets from a 25 wt % PS suspension,whereas microcapillary devices made from glass capillary tubes areable to produce droplets from a 67 wt % PS nanoparticle suspension.When the PS concentration is between 0.6 and 25 wt %, the size ofthe droplets is found to change with the oil-to-water flow rate ratioand is independent of the concentration of particles in the initialsuspensions. Drop sizes from ∼12 to 40 μm are made usingflow rate ratios Qoil/Qwaterfrom 20 to 1, respectively, with either of the PDMSdevices. However, clogging occurs in PDMS devices at high PS concentrations(>25 wt %) arising from interactions between the PS colloids andthesurface of PDMS devices. Glass microcapillary devices, on the otherhand, are resistant to clogging and can produce droplets continuouslyeven when the concentration of PS nanoparticles reaches 67 wt %. Webelieve that our findings indicate useful approaches and guidelinesfor the controlled generation of emulsions filled with a high loadingof nanoparticles, which are useful for drug delivery applications. [ABSTRACT FROM AUTHOR]