Palladium-catalyzed formation and reactions of iodo- and bromosiloxane intermediates

Polysiloxanes are useful materials because of their functionality, such as high thermal stability, electrical resistance, and hydrophobicity. In this regard, we studied palladium-catalyzed formation of iodo-and bromopolysiloxanes from two types of hydrosiloxanes, alpha,omega-dihydropoly(dimethylsiloxane) (1) and cyclotetra(hydromethylsiloxane) (2), and their reactions. Treatment of 1 with mixtures of cyclic ethers or lactones and MeI or allylBr in the presence of a catalytic amount of PdCl2 gave the corresponding alpha,omega-bis(haloalkoxy and haloalkanoyloxy) poly(dimethylsiloxane)s in good yields, via iodo-and bromopoly(dimethylsiloxane) intermediates. Transformation of the iodobutoxy-terminal units in the resulting poly(dimethylsiloxane) into aminoalkoxy groups was examined. The formation of alpha,omega-diiodo- and dibromopoly(dimethylsiloxane)s from 1 was confirmed by spectrometric analysis as well as by quenching experiments with ethanol. A reaction of alpha,omega-dibromopoly(dimethylsiloxane) with 2,5-dilithiothiophene gave a polydimethylsiloxane-thiophene alternating polymer. Similar palladiumcatalyzed reactions of 2 with THF/MeI, THF/allylBr, and delta-valerolactone/allylBr afforded cyclo(halobutoxy- and bromobutanoyloxymethylsiloxane) s in moderate yields. This would provide a new strategy for the introduction of various substituents to the terminal positions of linear polysiloxane and to the cyclosiloxane core

Synthesis, characterization, and photovoltaic applications of dithienogermole-dithienylbenzothiadiazole and -dithienylthiazolothiazole copolymers

New dithienogermole-based conjugated polymers were synthesized by the Stille coupling reactions of distannyldithienogermole and dibromoarene, and their photovoltaic properties were studied. These polymers possess low band gaps with broad absorptions covering the 400-800 nm range, and exhibit good film forming properties. Bulk hetero-junction solar cells prepared from blends of these polymers with PC(70)BM exhibit high power conversion efficiency up to 2.38%

Title Synthesis, characterization, and photovoltaic applications of dithienogermole-dithienylbenzothiadiazole and - dithienylthiazolothiazole copolymers Synthesis, characterization, and photovoltaic applications of dithienogermole-dithienylbenzothiadiazol

Abstract New dithienogermole-based conjugated polymers were synthesized by the Stille coupling reactions of distannyldithienogermole and dibromoarene, and their photovoltaic properties were studied. These polymers possess low band gaps with broad absorptions covering the 400-800 nm range, and exhibit good film forming properties. Bulk hetero-junction solar cells prepared from blends of these polymers with PC 70 BM exhibit high power conversion efficiency up to 2.38%

Synthesis of Group 14 Dipyridinometalloles with Enhanced Electron-Deficient Properties and Solid-State Phosphorescence

Silicon- and germanium-bridged bipyridyls were prepared, and their optical and electrochemical properties were investigated. It was found that they exhibited enhanced electron deficiency and phosphorescence properties in comparison to parent bipyridyl. The single-crystal structure of a dipyridinosilole and results of DFT calculations on models are also described

3-D Molecular Mixtures of Catalytically Functionalized [vinylSiO_1.5]₁₀/[vinylSiO_1.5]₁₂. Photophysical Characterization of Second Generation Derivatives

Fluoride ion catalyzed rearrangement of −[vinylSiO_1.5]_<i>n</i>– oligomers and polymers in THF (tetrahydrofuran) provides essentially quantitative conversion to mixtures of the three dimensional (3-D) cage compounds [vinylSiO_1.5]₁₀ and [vinylSiO_1.5]₁₂ with small amounts of the [vinylSiO_1.5]₁₄ cage. These mixtures are easily transformed into their respective styrenyl analogs by metathesis with <i>p-</i>R-styrene to give 100% conversion to the Generation 1 (GEN1) compounds [<i>p-</i>R-styrenylSiO_1.5]_10/12. The R = Br compounds are then easily modified by Heck coupling with <i>p-</i>R-styrene in >90% yields and ≈100% conversion to the Generation 2 (GEN2) compounds [<i>p-</i>R-stilbenevinylSiO_1.5]_10/12. These studies were designed to map structure–photophysical properties in these 3-D molecules with the goal of finding replacements for C₆₀ and C₇₀ electron acceptor compounds currently in use in most hybrid organic photovoltaics. Photophysical characterization indicates that the GEN2 compounds have average band gaps that are slightly smaller than their T₈ analogs. However, the C₆F₅ derivative offers blue-shifted absorption with a very red-shifted emission in contrast to the blue emission shift that was expected coincident with the absorption blue shift. Initial cyclic voltammetry studies suggest that the GEN2 C₆F₅ derivative has HOMO–LUMO energies that may, through further modification, provide energy levels that meet our target objectives. In addition, solvent studies targeting absorption and emission behavior find emission behavior in poor solvents for R = H, Me, MeO that suggests some form of aggregation. This aggregation red shifts emission, perhaps arising from partial interdigitation of <i>p-</i>R-stilbenevinyl groups. Because these molecules are 3-D, moieties opposite the points of interdigitation emit as they do in good solvents, leading to emissions that broadened greatly. Furthermore, because we have previously observed what appears to be 3-D conjugation in the excited state, these results suggest the potential to promote charge transport in three dimensions perhaps similar to C₆₀/C₇₀. Alternately, these same materials may serve as novel emitters for light emitting diodes