Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, we synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, we were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of our studies, we synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led us to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides;The utility of MTO as a Lewis acid was exploited in effecting the rearrangement of propargylic alcohols to enones and enals. This reaction works efficiently with MTO when the propargyl alcohol is benzylic. The same chemistry when extended to allylic alcohols generates the more stable isomer at equilibrium. Kinetic, 2D and 18O labelling and theoretical studies were carried out to establish the mechanism of this reaction and to predict the direction of equilibrium in these systems;MTO activates hydrogen peroxide by forming a monoperoxo and a bisperoxocomplex both of which are efficient oxidants. Substituted arenes are selectively oxidized to p-quinones by the MTO/H2O2 system. The partially oxidized hydroquinones were detected in a few cases

Swapping field-effect transistor characteristics in polymeric diketopyrrolopyrrole semiconductors: Debut of an electron dominant transporting polymer

A fact-finding study on thiophenyl diketopyrrolopyrrole (TDPP)-containing polymers for electronically convertible transport characteristics in organic field effect transistors (OFETs) is presented. In the subject of this consideration, a TDPP-based polymer with bis-benzothiadiazole (BisBT) units that serve as powerful electron-deficient building blocks, namely PDTDPP-BisBT, is prepared in order to achieve an n-channel transistor. The resulting polymer shows n-channel dominant ambipolar OFET characteristics and its electron mobility (1.3 x 10(-3) cm(2) V(-1) s(-1)) is found to be one order of magnitude higher than the hole mobility. Besides, the PDTDPP-BisBT OFET performance is independent of film-deposition conditions due to its completely amorphous microstructure, supported by the atomic force microscopy (AFM) and X-ray diffraction (XRD) analyses. Herein, we report an intriguing discovery in sync with our previous studies that TDPP-based polymers can function as a p-type, n-type, or ambipolar organic semiconductor in accordance with the degree of electron affinity of the comonomers.close211

Improving the layer morphology of solution-processed perylene diimide organic solar cells with the use of a polymeric interlayer

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Recent Advances in Conjugated Polymers for Light Emitting Devices

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review

Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, we synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, we were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of our studies, we synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led us to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides;The utility of MTO as a Lewis acid was exploited in effecting the rearrangement of propargylic alcohols to enones and enals. This reaction works efficiently with MTO when the propargyl alcohol is benzylic. The same chemistry when extended to allylic alcohols generates the more stable isomer at equilibrium. Kinetic, 2D and 18O labelling and theoretical studies were carried out to establish the mechanism of this reaction and to predict the direction of equilibrium in these systems;MTO activates hydrogen peroxide by forming a monoperoxo and a bisperoxocomplex both of which are efficient oxidants. Substituted arenes are selectively oxidized to p-quinones by the MTO/H2O2 system. The partially oxidized hydroquinones were detected in a few cases.</p

Synthesis and photochromic properties of ladderized poly (p-phenylene-alt-9,10-anthrylene)s

We report here the synthesis and characterization of stepladder and ladder poly(p-phenylene-alt-anthrylene)s (SLPPPA and LPPPA respectively) containing 9,10-anthrylene building groups within the main chain. The polyketone ladder polymer precursors are prepared by palladium-catalyzed Suzuki-type cross-coupling. The solution optical spectra of SLPPPA and LPPPA exhibit broad absorption bands with large Stokes shift unusual for rigid, ladder-type polymers. SLPPPA shows an intense yellow emission with a maximum at 584 nm while LPPPA is more red-shifted in emission with a maximum at 693 nm due to the penalization of the aromatic repeat units. Cyclic voltammetry studies reveal that both SLPPPA and LPPPA undergo fully reversible p- and n-doping processes. The methylene-bridged 1,4-di(10-phenylanthracen-9-yl)benzene LMC and the bis(methylene)bridged 9,10-diphenylanthracene SLMC are also synthesized, they serve as ladder and stepladder model compounds respectively and their optical properties are discussed in comparison with the above polymers. The stepladder derivatives (SLMC and SLPPPA) are found to form endoperoxides in the presence of visible light in a thermally reversible process whereas the ladder derivatives (LMC and LPPPA) undergo irreversible photooxidation.close242