The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Dwight S. Seferos - One of the best experts on this subject based on the ideXlab platform.
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examining structure property function relationships in thiophene selenophene and Tellurophene homopolymers
ACS Applied Energy Materials, 2018Co-Authors: Joseph G Manion, Andrew H Proppe, Arnaud W Laramee, George R Mckeown, Emily L Kynaston, Shana O Kelley, Edward H Sargent, Dwight S. SeferosAbstract:Heavy atom main group element-containing conjugated polymers have attracted increasing attention in recent years. The synthesis of these compounds is generally involved, and little is known about their optoelectronic device performance. Here we examine the relationship between polymer structure and optoelectronic behavior in a series of chalcogenophene homopolymers of thiophene, selenophene, and Tellurophene with well-matched molecular weights, dispersity, and regioregularity. We employ fast and slow drying device preparations to study the effect of polymer–fullerene separation on charge separation and collection in canonical bulk heterojunction photovoltaic cells. In both preparations, increasing heteroatom size leads to larger proportions of finely mixed polymer–fullerene domains. Differences in polymer–fullerene separation between preparations result in the formation of optimal morphologies in selenophene and Tellurophene devices with little impact on thiophene devices. We then use planar heterojunctio...
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Examining Structure–Property–Function Relationships in Thiophene, Selenophene, and Tellurophene Homopolymers
2018Co-Authors: Joseph G. Manion, Andrew H Proppe, George R Mckeown, Emily L Kynaston, Shana O Kelley, Edward H Sargent, Arnaud W. Laramée, Dwight S. SeferosAbstract:Heavy atom main group element-containing conjugated polymers have attracted increasing attention in recent years. The synthesis of these compounds is generally involved, and little is known about their optoelectronic device performance. Here we examine the relationship between polymer structure and optoelectronic behavior in a series of chalcogenophene homopolymers of thiophene, selenophene, and Tellurophene with well-matched molecular weights, dispersity, and regioregularity. We employ fast and slow drying device preparations to study the effect of polymer–fullerene separation on charge separation and collection in canonical bulk heterojunction photovoltaic cells. In both preparations, increasing heteroatom size leads to larger proportions of finely mixed polymer–fullerene domains. Differences in polymer–fullerene separation between preparations result in the formation of optimal morphologies in selenophene and Tellurophene devices with little impact on thiophene devices. We then use planar heterojunction devices to directly examine the effects of heteroatom substitution on charge transport and charge generation and find that in the absence of polymer–fullerene mixing, devices exhibit similar diode behavior. We further demonstrate that ultrafast decay pathways unique to heavy heteroatom-containing polymers are apparent in both planar and bulk heterojunctions and thus not dependent on polymer–fullerene mixing or polymer assembly. This work directly examines the role of heteroatom substitution in defining the photovoltaic performance of conjugated homopolymers. Through single-atom substitution we are able to significantly modify polymer assembly, mixing, and optoelectronic properties. Specific emphasis on Tellurophene polymers reveals relationships between polymer structure and properties that are not apparent in more traditional light-atom chalcogenophenes such as thiophene and selenophene
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Ring Opening of π‑Delocalized 2,5-DiphenylTellurophene by Chemical or Self-Sensitized Aerobic Photooxidation
2017Co-Authors: Elisa I. Carrera, Dwight S. SeferosAbstract:We report the self-sensitized aerobic photooxidation of 2,5-diphenylTellurophene (PT). Irradiation of PT induces rapid intersystem crossing to the triplet excited state, which undergoes energy transfer to oxygen to form singlet oxygen. Reaction of the heterocycle with singlet oxygen was found to occur at the carbon framework through a 1,4-cycloaddition reaction rather than at tellurium to form the Te(IV) telluroxide, as is commonly observed for other tellurium-containing heterocycles. This leads to oxidative ring-opening of the Tellurophene to form (Z)-1,4-diphenylbut-2-ene-1,4-dione ((Z)-ED) with extrusion of TeO2. In attempts to study the formation of the Te(IV) telluroxide and Te(VI) tellurone by chemical oxidation with m-chloroperoxybenzoic acid (mCPBA), we discovered that PT undergoes an oxidative ring-opening reaction to the same ene-dione product after reaction with 4 equiv of mCPBA. Extrusion of TeO2 was also observed in this case. This ring-opening reaction was studied in detail by NMR spectroscopy, GC-MS, and density functional theory calculations
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a mechanistic study of halogen addition and photoelimination from π conjugated Tellurophenes
Journal of the American Chemical Society, 2016Co-Authors: Elisa I. Carrera, Ann Julie Lough, Juan C. Scaiano, Anabel E. Lanterna, Dwight S. SeferosAbstract:The ability to drive reactivity using visible light is of importance for many disciplines of chemistry and has significant implications for sustainable chemistry. Identifying photochemically active compounds and understanding photochemical mechanisms is important for the development of useful materials for synthesis and catalysis. Here we report a series of photoactive diphenylTellurophene compounds bearing electron-withdrawing and electron-donating substituents synthesized by alkyne coupling/ring closing or palladium-catalyzed ipso-arylation chemistry. The redox chemistry of these compounds was studied with respect to oxidative addition and photoelimination of bromine, which is of importance for energy storage reactions involving X2. The oxidative addition reaction mechanism was studied using density functional theory, the results of which support a three-step mechanism involving the formation of an initial η1 association complex, a monobrominated intermediate, and finally the dibrominated product. All o...
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What Limits the Molecular Weight and Controlled Synthesis of Poly(3-alkylTellurophene)s?
2016Co-Authors: Marvin Steube, Elisa I. Carrera, Dwight S. SeferosAbstract:PolyTellurophenes are an emerging class of conjugated polymers; however, their controlled polymerization leading to high molecular weight materials has been a major challenge. Here we present a systematic investigation of the synthesis of poly(3-alkylTellurophene)s using the catalyst transfer polycondensation methodology. Learning that previous syntheses were limited by both polymerization reaction kinetics and polymer solubility, we design new Tellurophene monomers to overcome these limitations. Controlled polymerization behavior up to Mn = 25 kDa, chain extension, block copolymerization, external initiation, and well-defined end groups are demonstrated for poly(3-alkylTellurophene)s with appropriately designed side chains. We clarify the role that side-chain branching point plays on polymerization kinetics and optical properties for these prototypical regioregular polymers. In addition, the effect that monomer addition sequence has on well-defined Tellurophene–thiophene block copolymers was studied. The controlled polymerization of Tellurophene should provide access to more complex polymeric architectures involving these and other conjugated monomers. The methods used to optimize the polymerization of alkylTellurophenes should be applicable to other monomers that have been challenging to synthesize in a controlled manner
Raymond A Poirier - One of the best experts on this subject based on the ideXlab platform.
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comparison of geometries and electronic structures of polyacetylene polyborole polycyclopentadiene polypyrrole polyfuran polysilole polyphosphole polythiophene polyselenophene and polyTellurophene
Synthetic Metals, 1998Co-Authors: U Salzner, J B Lagowski, Peter G Pickup, Raymond A PoirierAbstract:Abstract Geometries of monomers through hexamers of cylopentadiene, pyrrole, furan, silole, phosphole, thiophene, selenophene and Tellurophene, and monomers through nonamers of borole were optimized employing density functional theory with a slightly modified B3P86 hybrid functional. Bandgaps and bandwidths were obtained by extrapolating the appropriate energy levels of trimers through hexamers (hexamers through nonamers for borole) to infinity. Bandgaps increase with increasing π-donor strengths of the heteroatom. In general, second period heteroatoms lead to larger bandgaps than their higher period analogs. Polyborole is predicted to have a very small or no energy gap between the occupied and the unoccupied π-levels. Due to its electron deficient nature polyborole differs significantly from the other polymers. It has a quinoid structure and a large electron affinity. The bandgaps of heterocycles with weak donors (CH 2 , SiH 2 and PH) are close to that of polyacetylene. For polyphosphole this is due to the pyramidal geometry at the phosphorous which prevents interaction of the phosphorus lone pair with the π-system. The bandgap of polypyrrole is the largest of all polymers studied. This can be attributed to the large π-donor strength of nitrogen. Polythiophene has the third largest bandgap. The valence bandwidths differ considerably for the various polymers since the avoided crossing between the flat HOMO — 1 band and the wide HOMO band occurs at different positions. The widths of the wide HOMO bands are similar for all systems studied. All of the polymers studied have strongly delecalized π-systems.
Henning Sirringhaus - One of the best experts on this subject based on the ideXlab platform.
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chalcogenophene comonomer comparison in small band gap diketopyrrolopyrrole based conjugated polymers for high performing field effect transistors and organic solar cells
Journal of the American Chemical Society, 2015Co-Authors: Raja Shahid Ashraf, Miquel Planells, Bob C. Schroeder, Iain Meager, Mark Nikolka, Mindaugas Kirkus, Sarah Holliday, Michael Hurhangee, Christian B Nielsen, Henning SirringhausAbstract:The design, synthesis, and characterization of a series of diketopyrrolopyrrole-based copolymers with different chalcogenophene comonomers (thiophene, selenophene, and Tellurophene) for use in field-effect transistors and organic photovoltaic devices are reported. The effect of the heteroatom substitution on the optical, electrochemical, and photovoltaic properties and charge carrier mobilities of these polymers is discussed. The results indicate that by increasing the size of the chalcogen atom (S < Se < Te), polymer band gaps are narrowed mainly due to LUMO energy level stabilization. In addition, the larger heteroatomic size also increases intermolecular heteroatom–heteroatom interactions facilitating the formation of polymer aggregates leading to enhanced field-effect mobilities of 1.6 cm2/(V s). Bulk heterojunction solar cells based on the chalcogenophene polymer series blended with fullerene derivatives show good photovoltaic properties, with power conversion efficiencies ranging from 7.1–8.8%. A hi...
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Chalcogenophene Comonomer Comparison in Small Band Gap Diketopyrrolopyrrole-Based Conjugated Polymers for High-Performing Field-Effect Transistors and Organic Solar Cells
2015Co-Authors: Raja Shahid Ashraf, Miquel Planells, Bob C. Schroeder, Iain Meager, Mark Nikolka, Mindaugas Kirkus, Sarah Holliday, Michael Hurhangee, Christian B. Nielsen, Henning SirringhausAbstract:The design, synthesis, and characterization of a series of diketopyrrolopyrrole-based copolymers with different chalcogenophene comonomers (thiophene, selenophene, and Tellurophene) for use in field-effect transistors and organic photovoltaic devices are reported. The effect of the heteroatom substitution on the optical, electrochemical, and photovoltaic properties and charge carrier mobilities of these polymers is discussed. The results indicate that by increasing the size of the chalcogen atom (S < Se < Te), polymer band gaps are narrowed mainly due to LUMO energy level stabilization. In addition, the larger heteroatomic size also increases intermolecular heteroatom–heteroatom interactions facilitating the formation of polymer aggregates leading to enhanced field-effect mobilities of 1.6 cm2/(V s). Bulk heterojunction solar cells based on the chalcogenophene polymer series blended with fullerene derivatives show good photovoltaic properties, with power conversion efficiencies ranging from 7.1–8.8%. A high photoresponse in the near-infrared (NIR) region with excellent photocurrents above 20 mA cm–2 was achieved for all polymers, making these highly efficient low band gap polymers promising candidates for use in tandem solar cells
Jochen Autschbach - One of the best experts on this subject based on the ideXlab platform.
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calculation of the magnetic circular dichroism b term from the imaginary part of the verdet constant using damped time dependent density functional theory
Journal of Chemical Physics, 2007Co-Authors: Mykhaylo Krykunov, Tom Ziegler, Michael Seth, Jochen AutschbachAbstract:A time-dependent density functional theory (TDDFT) formalism with damping for the calculation of the magnetic optical rotatory dispersion and magnetic circular dichroism (MCD) from the complex Verdet constant is presented. For a justification of such an approach, we have derived the TDDFT analog of the sum-over-states formula for the Verdet constant. The results of the MCD calculations by this method for ethylene, furan, thiophene, selenophene, Tellurophene, and pyrrole are in good agreement with our previous theoretical sum-over-states MCD spectra. For the π→π* transition of propene, we have obtained a positive Faraday B term. It is located between the two negative B terms. This finding is in agreement with experiment in the range of 6–8eV.
S M S Chauhan - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Selenium and Tellurium Core-Modified Azuliporphyrinogens and Benziporphyrinogens and Corresponding Carbaporphyrinoids
2018Co-Authors: Sohail Ahmad, Anchal Singhal, Kharu Nisa, S M S ChauhanAbstract:The synthesis of selenium and tellurium core-modified carbaporphyrinogens was carried out by the reaction of functional selenophene/Tellurophene diols with azulene or a benzitripyrrane in the presence of acid. The products were obtained in moderate yields and were characterized by using 1H and 13C NMR, UV–vis, FT-IR, CV, and HRMS spectroscopic techniques. Further, oxidation of the obtained core-modified carbaporphyrinogens in the presence of DDQ in CHCl3 afforded the corresponding carbaporphyrins in good yields. Benziporphyrins showed no indication of a ring current or macrocyclic aromaticity as confirmed by using proton NMR spectroscopy, but the addition of TFA gave rise to the formation of weakly diatropic dications
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Synthesis of 21,23-Selenium- and Tellurium-Substituted 5‑Porphomethenes, 5,10-Porphodimethenes, 5,15-Porphodimethenes, and Porphotrimethenes and Their Interactions with Mercury
2015Co-Authors: Sohail Ahmad, Kumar Karitkey Yadav, Soumee Bhattacharya, Prashant Chauhan, S M S ChauhanAbstract:The 3+1 condensation of symmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/Tellurophene-2,5-diols in the presence of BF3-etheratre or BF3-methanol followed by oxidation with DDQ gave 5,10-porphodimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/Tellurophene-2,5-diols gave 5-porphomethenes. In addition, the reaction of unsymmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/Tellurophene-2,5-diols gave the corresponding porphotrimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/Tellurophene-2,5-diols gave the 5,15-porphodimethenes. The structures of different products were characterized by IR, 1H and 13C NMR, 1H–1H COSY, CHN analysis, and mass spectrometry. The binding of mercury with the calix[4]phyrins mentioned above had been observed in the decreasing order of porphodimethenes > porphomethenes > porphotrimethenes by UV–vis and 1H NMR spectroscopy
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synthesis of 5 10 15 20 meso unsubstituted and 5 10 15 20 meso substituted 21 23 ditellura diselena core modified porphyrinogens oxidation and detection of mercury ii
RSC Advances, 2014Co-Authors: Sohail Ahmad, Kumar Karitkey Yadav, Sarangthem Joychandra Singh, S M S ChauhanAbstract:Tellurium and selenium incorporated 5,10,15,20-meso-unsubstituted-21,23-ditellura/diselena core-modified porphyrinogens (N2Te2 and N2Se2), 5,10,15,20-meso-unsubstituted-21-tellura/selena core-modified porphyrinogens (N3Te and N3Se) and fully substituted meso-carbons porphyrinogens (N2Te2, N2Se2 and higher analogs) are synthesized by 3 + 1 condensation of Tellurophene/selenophene dipyrranes and their corresponding diols in the presence of BF3–etharate or BF3–methanol. The meso-unsubstituted and substituted porphyrinogens were oxidized with chloranil/0.1% aqueous FeCl3 in CHCl3 at room temperature to obtain the corresponding porphines and porphyrins which are further reduced to corresponding chlorin and bacteriochlorin, whereas the fully meso-substituted porphyrinogens were found to be good ligands for Hg2+. The structures of the products were characterized by IR, 1H, 13C, 125Te, 77Se NMR, CHN analysis, mass spectrometry and single-crystal XRD.
