Organic semiconductors (OSCs) are important active materials for the fabrication of next-generation organic-based electronics. However, the development of n-type OSCs lags behind that of p-type OSCs in terms of charge-carrier mobility and environmental stability. This is due to the absence of molecular designs that satisfy the requirements. The present study describes the design and synthesis of n-type OSCs based on challenging molecular features involving a π-electron core containing electronegative N atoms and substituents. The unique π-electron system simultaneously reinforces both electronic and structural interactions. The current n-type OSCs exhibit high electron mobilities with high reliability, atmospheric stability, and robustness against environmental and heat stresses and are superior to other existing n-type OSCs. This molecular design represents a rational strategy for the development of high-end organic-based electronics.
Poly[1,2,(4)-phenylenevinyleneanisylaminium] 1 was synthesized by one-pot palladium-catalyzed polycondensation of N-(3-bromo-4-vinylphenyl)-N-(4-methoxyphenyl)-N-(4-vinylphenyl)amine 3 and subsequent oxidation with the thianthrene cation radical tetrafluoroborate: compound 1 three-directionally satisfies a non-Kekulé-type pi-conjugation and the ferromagnetic connectivity of the unpaired electrons of the triarylaminium cationic radical. The average molecular weight of the polymer was 4700-5900 (degree of polymerization = 11-14), which gave a single molecular-based and globular-shaped image of ca. 15 nm diameter by atomic and magnetic force microscopies under ambient conditions. The aminium polyradical 1 with a spin concentration (determined by iodometry) of 0.65 spin/unit displayed an average S (spin quantum number) value of 7/2 even at 70 degrees C according to NMR and magnetization measurements.
Variation
of aggregated structures driven by side chains is a crucial
issue in organic semiconductors (OSCs) for achieving high carrier
mobility and device durability. In this work, phenylalkyl side chains
composed of a rigid terminal phenyl group and a flexible alkyl linker
were studied based on a state-of-the-art n-type π-electron system,
3,4,9,10-benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI), from the viewpoints of
aggregated structures and thin-film transistors. An appropriate length
of the alkyl, i.e., propyl, linker led to stable formation of a unique
aggregated structure regardless of solution-grown single-crystal and
vacuum-deposited polycrystalline thin films likely due to cooperation
of rigid phenyl and flexible alkyl moieties. In contrast, a shorter
ethyl linker showed polymorphism in the polycrystalline film. An absence
of polymorphism did not only result in high mobility and low threshold
voltage but also show low contact resistance. Hence, this work proposes
opportunities to design n-type OSCs by introduction of both rigid
and flexible characters to the side chains.
[reaction: see text] A new triradical molecule, 2,6,10-tris(dianisylaminium)-3,7,11-tris(hexyloxy)triphenylene 1(3+), was synthesized by oxidative trimerization, palladium-catalyzed amination, and subsequent oxidation. It was chemically stable with a half-life > 1 month and displayed the magnetic parameter of S = 3/2 even at room temperature.
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