ABSTRACT Oxidative organic transformation has emerged as a powerful strategy for C─C and C–heteroatom bond forming reaction. In this study, a completely metal free, oxidative desulfitative C─N coupling has been realized harnessing C─S bond as the electrophilic partner at room temperature in eco‐benign solvent ethanol. The thio‐amide group present in 5‐isatinylidene‐rhodanine has been utilized as a source of C─S bond. C─N coupling with amine is realized using TEMPO as an organo‐catalyst. Molecular oxygen has been exploited as the terminal oxidant. No additives or strong base are required for this reaction. Notably, this C─N coupling occurs at room temperature avoiding dry solvent or inert atmosphere. The pure product can be obtained just by filtration and recrystallization from ethanol. This significantly minimizes the use of toxic organic solvents. The protocol is extremely reproducible and product yields are very high. All these features make this transformation environmentally benign and very much pertinent for the construction of C─N bonds in a sustainable way.

In this study, an amalgamation between multicomponent (MCR) strategy and organocatalysis for the synthesis of pyrroloacridine derivatives starting from 4,4-dimethylcyclohexane-1,3-dione, amines, and isatin has been reported in eco-friendly solvent EtOH. Since, here the cyclic 1,3-diketone being used is structurally unsymmetrical; there is possibility of formation of two different products. However, the reaction shows very high regioselectivity and produces one product almost exclusively. Moreover, use of adipic acid as an organo-catalyst, EtOH as eco-benign solvent and moderate reaction temperature align this reaction with the postulates of green chemistry. The reaction shows high reproducibility and broad substrate tolerance. The synthesized pyrroloacridine molecules have great application in the field of medicinal chemistry and material sciences. All these features make this present work worthy to disclose to broad scientific community.

A metal free oxidative desulfitative C−N coupling reaction through activation of latent thiol group using hypervalent iodine reagent is being reported in eco‐friendly solvent ethanol. Here, the thio‐amide group present in 5‐alkylidene‐rhodanine has been utilized as latent thiol functionality and C−N coupling with amines is realized. The reaction occurs evading the use of metal catalysts, inert atmosphere, high temperature or microwave heating, and strong base which is normally required for metal catalyzed C−N coupling reaction. Pertinently, here poorly nucleophilic aromatic amines react very efficiently. Desulfitative C−N coupling involving free thiol moiety and poorly nucleophilic aromatic amines in metal free condition has never been accomplished in one step, without requiring high temperature microwave heating or strong bases. The reaction occurs at just 50 °C in few hours under ambient atmosphere. Moreover, here no H 2 S is released in the environment, since solid sulphur is precipitated out as side product, making this protocol environmentally friendly. Metal free condition, low temperature, use of non‐toxic solvent and reagent, prevention of the release of H 2 S in the environment make this protocol very much environmentally friendly and highly suitable for C−N coupling in a sustainable way.

5-Hydroxy-1H-pyrrol-2-ones represent a very important class of compounds. However, their syntheses rely on precursors that are exotic and commercially unavailable, or on multistep operations. A cascade reaction can evade multistep syntheses, but most substrates are not amenable to cascade strategies. We thoughtfully designed a cascade strategy, choosing the Knoevenagel product of a ketone and malononitrile as a very trivial starting material. This strategy afforded 5-hydroxy-1H-pyrrol-2-ones via a cascade of C(sp3)-H functionalization, directed nitrile hydrolysis and C-N bond-forming reactions.

Direct oxidation of sp 3 C─H bond is an extremely important part of modern‐day research in both academia and industry, because of the ubiquities of C─H bond in organic and biomolecules. However, challenges remain with regard to site‐selectivity and environmental concerns, since mostly transition metals and hazardous oxidants are used. In this work, we disclose two different transition‐metal‐free oxidative approaches for the selective oxidation of heterobenzylic sp 3 C─H bond in the presence of other oxidizable C─H bonds, like benzylic C─H and more reactive C(sp 2 )─H. We initially developed a visible light‐assisted photocatalytic oxidation of the heterobenzylic C─H bond using Eosin Y (EY) as photocatalyst and K 2 S 2 O 8 as nontoxic terminal oxidant affording corresponding heteroaryl ketones. In another approach, the same reaction was performed in the absence of any photocatalyst or light, using TEMPO as the catalyst and K 2 S 2 O 8 as the oxidant. The reactions occur under ambient atmosphere, at very low temperatures, and exhibit high selectivity for the heterobenzylic C─H bond.

2‐Thioxo‐4‐thiazolidinone which is trivially known as rhodanine is a five‐membered heterocycle, containing a sulfur and nitrogen atom at 1 and 3 positions, respectively. It is a very attractive class of compounds, because derivatization of rhodanine yields a number of molecules having multifarious application in medicinal chemistry and biology. There are many molecules derived from rhodanine which are already being used commercially as drug molecules. So owing to the importance of rhodanine in the field of medicinal chemistry and biology, a comprehensive review familiarizing different derivatives of the parent molecule rhodanine and their syntheses is highly warranted. In this review, we have broadly categorized the reactions of rhodanine as; (a) Knoevenagel condensation through the C‐5 active methylene group with carbonyl compounds, (b) nucleophilic attack on thioxo group at position 2 of rhodanine by aliphatic amines, (c) thioxo to oxo conversion, and (d) all other reactions. So far, to the best of our knowledge, no such literature which accounts for all the different kinds of reactions of rhodanine is reported. Here, we have not only presented the reactions schemes from various literatures, but we have discussed about the advantages and inadequacies of that particular catalytic processes. Moreover, at the end of this article we have given our own critical analysis on these literature reports, based on our understanding and experience.

Visible-light assisted a very simple and mild protocol for photocatalytic oxidative transformation of thioamide to amide group has been realized in cyclic system. For this purpose 5-arylalkylidene-rhodanine derivatives were chosen as model substrates to afford thiazolidine-2,4-diones. Light mediated reactions are intrinsically beneficial, since activation occurs by cleanest energy source light. Here K2S2O8 is used as terminal oxidant which does not leave any hazardous and corrosive waste to discard after the reaction fostering the practices of green chemistry. This is the first report of conversion of thioxo group in rhodanine derivatives into the corresponding oxygen analogue by visible light photo-catalytic method. The reaction was very general since various 5-arylalkylidene-rhodanines underwent the reaction smoothly affording high product yields. Moreover, the broadness of this protocol was further established by applying this reaction on other systems like 3,4-dihydropyrimidine-2(1H)-(thio)ones. A general Eosin Y catalyzed oxidative transformation of thioamide to amide group in cyclic systems taking 5-arylalkylidene-rhodanine as the model substrate under mild condition harnessing the environment friendly aspects of visible light have been accomplished. image

Selective epoxidation of olefins is a very important reaction as epoxides are widely been used as platform chemical in polymer and pharmaceutical industries. Unlike conventional oxidants like molecular O-2 or peroxides, the use of CO2 as a soft oxidant for the oxidation of olefins is very challenging as it offers the utilization of waste and plentiful CO2 together with the potential for the mitigation of its harmful environmental effect. Thus, this process is cost effective and environmentally challenging. Herein, we report the synthesis of a new crystalline porous organosilica material TSOS-1 with orthorhombic crystal structure by using a tailor made bridging organoslilane precursor prepared through the Schiff base condensation of p-terphenyl-4,4 ''-dialdehyde and 3-aminopropyl-trimethoxysilane. This novel crystalline material TSOS-1 has been synthesized hydrothermally in the absence of any structure-directing agent and it showed high BET surface area (220 m(2) g(-1)) and nanoscale porosity. TSOS-1 is used as a support for stabilizing tiny AgNPs to obtain a robust nanocatalyst Ag@TSOS-1, which efficiently catalyses the conversion of styrene into predominantly styrene oxide (SO) using CO2 as a soft oxidant in an autoclave reactor under mild reaction conditions.

A heterogeneous and magnetically recyclable Ni-chitosan nanocatalyst was synthesized and thoroughly characterized by powder Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, etc. It was effectively utilized in the eco-friendly synthesis of new C5-C6-unsubstituted 1,4-DHPs under ultrasonic irradiation. The important focus of the methodology was to develop an environmentally friendly protocol with a short reaction time and a simple reaction procedure. The other advantages of this protocol are a wide substrate scope, a very good product yield, the use of an eco-friendly solvent and a recyclable nanocatalyst, as well as reaction at room temperature.

AbstractAn efficient diastereoselective trans cyclopropanation of 3-alkylidene oxindoles with in situ generated α-diazo carbonyl compounds or α,β-unsaturated diazo compounds under metal-free conditions has been developed to synthesize 3-spirocyclopropyl-2-oxindole derivatives. The procedure is based on the 1,3-dipolar character of the corresponding diazo compounds under base-catalyzed conditions. The method has a wide substrate scope and uses easily available starting materials.

Probing structural changes of a molecule induced by charge transfer is important for understanding the physicochemical properties of molecules and developing new electronic devices. Here, we interrogate the structural changes of a single diketopyrrolopyrrole (DPP) molecule induced by charge transport at a high bias using scanning tunneling microscope break junction (STM-BJ) techniques. Specifically, we demonstrate that application of a high bias increases the average nonresonant conductance of single Au-DPP-Au junctions. We infer from the increased conductance that resonant charge transport induces planarization of the molecular backbone. We further show that this conformational planarization is assisted by thermally activated junction reorganization. The planarization only occurs under specific electronic conditions, which we rationalize by ab initio calculations. These results emphasize the need for a comprehensive view of single-molecule junctions which includes both the electronic properties and structure of the molecules and the electrodes when designing electrically driven single-molecule motors.

An ultrasound assisted efficient, expeditious and environmentally benign new methodology for direct access to broad ranges of structurally interesting and pharmacologically significant spiropyrido[2,1-b][1,3]oxazino compounds based on three component reactions approach via domino 1,4-dipolar cycloaddition from easily available starting materials in aq. ethanol medium at room temperature (25-30 degrees C) has been developed. In comparison to that of conventional methods, simple experimental and workup procedure, excellent yields, good functional group tolerance, cleaner reaction profile, use of green solvent are remarkable features of this sonochemical procedure.Furthermore, using of the ultrasound in this methodology leads to the reduction of the reaction times.

u Doping of organic semiconductors enhances the performance of optoelectronic devices. Although p-type doping is well studied and successfully deployed in optoelectronic devices, air stable n-type doping was still elusive. We succeeded with n-type doping of organic semiconductors using molecular dopant N-DMBI under ambient conditions. Strikingly, n-type doping accounts for a gigantic increase of the photoconductivity of doped thin films. Electrical and optical properties of the n-doped molecular semiconductor were investigated by temperature dependent conductivity, electron paramagnetic resonance (EPR), and flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. A significant reduction and saturation in activation energy with increasing doping level clearly suggests the formation of an impurity band and enhancement in carrier density. Computational studies reveal the formation of a charge transfer complex mediated by hydrogen abstraction as the rate-determining step for the doping mechanism. The colossal enhancement of photoconductivity induced by n-doping is a significant step toward optoelectronic devices made of molecular semiconductors.

Molecular architectures possessing the combination of heteroaromatic and saturated N-heterocycles are of great importance because of their higher solubility in the gastrointestinal tract due to weak crystal packing in the three-dimensional structure. Other biological activity like selectivity is also increased in a positive way. However, compared to fully aromatic fused heterocycles, synthesis of partially saturated fused heterocycles is much more difficult since the later needs greater control over the reaction conditions. In this context, 1,2,3,4-tetrahydronaphthyridines (THNADs) are essential part of pharmaceutically important natural products and drug molecules. However, the synthesis of THNAD is seldom reported in literature. To the best of our knowledge, this is the first report of metal-free one pot synthesis of 1,2,3,4-tetrahydro-1,6-naphthyridines without starting from any nitrogen heterocycles in water. Moreover, this study discloses the involvement of isocyanide in a chemical reaction whose net effect is only to reduce a C=C bond which is unusual in isocyanide literature.

Non-aqueous Redox Flow Batteries (RFBs) exploiting the wider electrochemical potential gap between catholyte and anolyte operate at higher cell voltages and lead to high energy and power densities with compelling energy efficiencies. However, stable anolytes are rare, primarily due to their low stability in presence of oxygen and moisture. The inherent atmospheric reactivity of anolyte puts a formidable demand to judiciously design molecules with high electron affinity and electrochemical stability. In this study, a non-aqueous organic RFB utilizing the redox pair is demonstrated employing commercially available Unisol blue (UB) dye (1,4-bis(isopropylamino) anthraquinone) as catholyte and air stable diketopyrrolopyrrole (DPP)-based derivative as anolyte. Cyclic voltammetry measurements with repeated sweep scans over 200 cycles are performed to find the redox potentials for both materials and electrochemical stability of the redox couple. The electrochemical performance of the RFB is studied by assembling cell with UB and DPP as redox pair. The study opens up a route to design/select molecules for non-aqueous RFBs.

An important strategy for realizing flexible complementary circuits with organic semiconductors is to achieve balanced ambipolar charge transport properties with reduced anisotropy. Here, we present a series of star-shaped diketopyrrolopyrrole (DPP)-based organic materials synthesized for improved intermolecular charge transport while retaining the ambipolar charge transport properties of their linear counterparts. Steady-state UV-visible spectroscopic studies confirm that the oligomers are highly aggregated in the thin film as evidenced from appearance of prominent vibronic features and red-shifted absorption bands. Ambipolar transport properties of these materials were verified in organic field-effect transistors (OFETs). The results show that the star-shaped DPP systems have the potential to outperform their linear counterparts in devices.

Organic-inorganic interfaces in photodiodes have recently gathered significant interest due to the realization of intrinsic p-n junctions and unique physical properties. Nanopatterned sol-gel ZnO films provide an alternate path for fullerene-free organic photodetectors. However, naturally occurring oxygen vacancies in ZnO often act as trap sites and can degrade device performance if left unchecked. Here, we focus on the role of UV-ozone treatment for filling oxygen vacancies in sol-gel processed ZnO for improving the hybrid interface with thienothiophene linked diketopyrrolopyrrole (DPP) films. The ZnO films are characterized by X-ray diffraction, ultraviolet photoelectron spectroscopy (UPS), cross-sectional electron microscope images, and electron energy loss spectroscopy (EELS). UV-ozone treatment shows no change in the crystal structure, but UPS indicates that the treated films are more resistive and have a higher oxygen concentration at the surface. The EELS spectra show gradual passivation of oxygen vacancies within the bulk of the ZnO films. Fullerene-free photodetectors fabricated from ZnO:DPP interfaces show dark currents reduced by half and photoresponsivities nearly doubled, on average, when the ZnO surface is UV-ozone treated compared to nontreated ZnO films, indicating this simple technique to be excellent for improving photodiode performance when ZnO is used as an electron transport layer.

One of the possible causes of degradation of perovskite solar cells is the instability of the electron transporting layer. In this regard, design of air stable electron transport organic semiconductors, compatible with perovskite energy levels presents challenges due to inherent vulnerability to traps, presumably originating due to water and/or oxygen. In this work, we demonstrate air stability of diketopyrrolopyrrole-based molecule (TDPP-CN4) at ambient conditions and its application as electron transporting layer (ETL) in perovskite solar cells. We investigated electron mobility and air stability of TDPP-CN4 by fabricating top-gate bottom-contact (TG-BC) thin film transistors and compared with PCBM at ambient conditions. Both TDPP-CN4 and PCBM exhibit electron transport properties with mobility of 0.13 cm(2) V-1 s(-1) and 0.03 cm(2) V-1 s(-1) respectively. However, we found remarkable air stability of the TDPP-CN4 in the OFET measurements under ambient conditions. These excellent properties of TDPP-CN4 render them as potential ETL layer in inverted planar heterojunction perovskite solar cells. Our preliminary device studies show remarkable short-circuit current (J(sc)) similar to 17.4 mA/cm(2) with moderate open-circuit voltage (V-oc) of 0.50 V. These results suggest that the electron mobility and air-stability of diketopyrrolopyrrole-based molecule hold a promise as Ell in perovskite solar cells at ambient conditions.

Hybrid organic-inorganic semiconducting interfaces have attracted attention in photodiodes and field-effect transistors (FETs) due to the realization of intrinsic p-n junctions and their mechanical flexibility. With the difficulty of developing high-mobility n-type organic semiconductors due to the necessity of low LUMO levels and ambient environment stability, solution processable inorganic materials are an excellent alternative. ZnO is an intrinsic n-type semiconductor which is non-toxic and sol-gel processable, creating avenues for film patterning and fully solution processed devices. We report the improvement of electron mobilities in ZnO FETs through simple UV-Ozone processing which reduces lattice defects within the film and at the SiO_2/ZnO interface. Treated ZnO films yield electron mobilities close to 10^−2 cm^2/Vs and on/off current ratios of 10^4 while non-treated films have mobilities on the order of 10^−5 cm^2/Vs and an order of magnitude lower on/off current ratios. Treated films also yield improved photoresponsivity and detectivity in hybrid ZnO-organic photodetectors.