Electron-deficient Building Block Research Articles

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 × 10−3 cm2 V−1 s−1) is found to be one order of magnitude higher than the hole mobility. Besides, the PDTDPP–BisBTOFET 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.

O,O′-Disubstituted N,N′-Dihydroxynaphthalenediimides (DHNDI): First Principles Designed Organic Building Blocks for Materials Science

N,N'-Disubstituted naphthalenediimides (NDIs), planar, electron-deficient building blocks, play an important role in materials and biological sciences. Naphthalene core substituents control the HOMO and LUMO energies, whereas the N-alkyl or aryl substituents affect the solubility, aggregation, and packing propensity in condensed phases. N,N'-Dihydroxynaphthalenediimide (DHNDI) allows expanding the chemical diversity by O-alkylation, acylation, or sulfonylation; these derivatives also allow fine-tuning of the HOMO/LUMO levels. The synthesis, UV-vis, electrochemical, solid state, and computational prediction of the properties of such derivatives are presented.

Alternating Copolymers of Dithienyl-s-Tetrazine and Cyclopentadithiophene for Organic Photovoltaic Applications

As a new emerging electron deficient building block, s-tetrazine (Tz) shows high electron affinity, which is even higher than the commonly used benzothiadiazole units. This property makes Tz a very promising electron withdrawing unit for low band gap conjugated polymers, especially for organic solar cell materials. We report the synthesis and property of five alternating copolymers of s-tetrazine and cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT), which are bridged with a thiophene unit. Methyl, hexyl, and/or 2-ethylhexyl groups are introduced onto thiophene and CPDT units to tune the solubility, UV absorption, frontier molecular orbital energy levels, and interchain stacking property of the resulting polymers. These polymers are stable up to 220 °C and decompose to dinitrile compounds with the breaking of Tz linkage at a higher temperature. Efficient bulk heterojunction solar cells were fabricated by blending these polymers with (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM), and they reached a power co...

Synthesis and applications of difluorobenzothiadiazole based conjugated polymers for organic photovoltaics

A new electron deficient building block, difluorobenzothiadiazole (FBT) was designed and synthesized for the first time. Two low band gap polymers containing this unit or benzothiadiazole (BT) and an electron rich unit, benzo[1,2-b:4,5-b′]dithiophene (BDT) were synthesized by Stille coupling reaction. It was found that fluorine substitution significantly lowered the energy levels but did not affect the UV absorption properties of the polymer. Comparatively, the fluorinated polymer showed a higher melting point and a reduced solubility. The electrical and photovoltaic properties of these polymers were studied by fabricating thin film transistors and polymer solar cells. The solar cell based on FBT polymer and PC71BM gives power conversion efficiency up to 3.4% under AM 1.5 G illumination (100 mW cm−2).