Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4-c]pyrrole-4,6-dione and Bithiopheneimide Photovoltaic Copolymers.

As effective building blocks for high-mobility transistor polymers, oligothiophenes are receiving attention for polymer solar cells (PSCs) because the resulting polymers can effectively suppress charge recombination. Here we investigate two series of in-chain donor-acceptor copolymers, PTPDnT and PBTInT, based on thieno[3,4-c]pyrrole-4,6-dione (TPD) or bithiopheneimide (BTI) as electron acceptor units, respectively, and oligothiophenes (nTs) as donor counits, for high-performance PSCs. Intramolecular S···O interaction leads to more planar TPD polymer backbones, however backbone torsion yields greater open-circuit voltages for BTI polymers. Thiophene addition progressively raises polymer HOMOs but marginally affects their band gaps. FT-Raman spectra indicate that PTPDnT and PBTInT conjugation lengths scale with nT catenation up to n = 3 and then saturate for longer oligomer. Furthermore, the effects of oligothiophene alkylation position are explored, revealing that the alkylation pattern greatly affects film morphology and PSC performance. The 3T with "outward" alkylation in PTPD3T and PBTI3T affords optimal π-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm(2)/(V s)). These characteristics contribute to the exceptional ∼80% fill factors for PTPD3T-based PSCs with PCE = 7.7%. The results demonstrate that 3T is the optimal donor unit among nTs (n = 1-4) for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering, transmission electron microscopy, and time-resolved microwave conductivity measurements reveal that the terthiophene-based PTPD3T blend maintains high crystallinity with appreciable local mobility and long charge carrier lifetime. These results provide fundamental materials structure-device performance correlations and suggest guidelines for designing oligothiophene-based polymers with optimal thiophene catenation and appropriate alkylation pattern to maximize PSC performance.

Substantial photovoltaic response and morphology tuning in benzo[1,2-b:6,5-b']dithiophene (bBDT) molecular donors.

The influence of solubilizing substituents on the photovoltaic performance and thin-film blend morphology of new benzo[1,2-b:6,5-b']dithiophene (bBDT) based small molecule donor semiconductors is investigated. Solar cells based on bBDT(TDPP)2-PC71BM with two different types of side chains exhibit high power conversion efficiencies, up to 5.53%.

Practical azidation of 1,3-dicarbonyls.

An operationally simple, direct azidation of 1,3-dicarbonyl compounds has been developed. The reaction proceeds readily under ambient conditions using sodium azide and an iodine-based oxidant such as I(2) or 2-iodoxybenzoic acid (IBX)-SO(3)K/NaI. In particular, the latter method, as a new and well-balanced oxidizing agent, shows excellent functional group tolerance and substrate scope and thus allows access to a variety of tertiary 2-azido and 2,2-bisazido 1,3-dicarbonyl compounds that would be more difficult to access by using traditional methods. Because the azide-containing products easily undergo 1,3-dipolar cycloaddition with alkynes, our report represents a novel route to analogues of sensitive complex molecules.

One-pot synthesis of 1,2-dihydropyridines: expanding the diverse reactivity of propargyl vinyl ethers.

The catalyzed synthesis of 1,2-dihydropyridines starting from easily accessible propargyl vinyl ethers was realized. The reaction sequence involving a transition metal-catalyzed propargyl-Claisen rearrangement, a condensation step, and a Brønsted acid-catalyzed heterocyclization furnishes the highly substituted heterocycles in moderate to excellent yields. Additionally, a practical one-pot protocol toward 1,2-dihydropyridines and 2H-pyrans starting from propargylic alcohols was developed.