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- ItemPersistent peri-Heptacene: Synthesis and In Situ Characterization(Weinheim : Wiley-VCH, 2021) Ajayakumar, M.R.; Ma, Ji; Lucotti, Andrea; Schellhammer, Karl Sebastian; Serra, Gianluca; Dmitrieva, Evgenia; Rosenkranz, Marco; Komber, Hartmut; Liu, Junzhi; Ortmann, Frank; Tommasini, Matteo; Feng, Xinliangn-peri-Acenes (n-PAs) have gained interest as model systems of zigzag-edged graphene nanoribbons for potential applications in nanoelectronics and spintronics. However, the synthesis of n-PAs larger than peri-tetracene remains challenging because of their intrinsic open-shell character and high reactivity. Presented here is the synthesis of a hitherto unknown n-PA, that is, peri-heptacene (7-PA), in which the reactive zigzag edges are kinetically protected with eight 4-tBu-C6H4 groups. The formation of 7-PA is validated by high-resolution mass spectrometry and in situ FT-Raman spectroscopy. 7-PA displays a narrow optical energy gap of 1.01 eV and exhibits persistent stability (t1/2≈25 min) under inert conditions. Moreover, electron-spin resonance measurements and theoretical studies reveal that 7-PA exhibits an open-shell feature and a significant tetraradical character. This strategy could be considered a modular approach for the construction of next-generation (3 N+1)-PAs (where N≥3). © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemWave-shaped polycyclic hydrocarbons with controlled aromaticity(Cambridge : RSC, 2019) Ma, Ji; Zhang, Ke; Schellhammer, Karl Sebastian; Fu, Yubin; Komber, Hartmut; Xu, Chi; Popov, Alexey A.; Hennersdorf, Felix; Weigand, Jan J.; Zhou, Shengqiang; Pisula, Wojciech; Ortmann, Frank; Berger, Reinhard; Liu, Junzhi; Feng, XinliangControlling the aromaticity and electronic properties of curved π-conjugated systems has been increasingly attractive for the development of novel functional materials for organic electronics. Herein, we demonstrate an efficient synthesis of two novel wave-shaped polycyclic hydrocarbons (PHs) 1 and 2 with 64 π-electrons. Among them, the wave-shaped π-conjugated carbon skeleton of 2 is unambiguously revealed by single-crystal X-ray crystallography analysis. The wave-shaped geometry is induced by steric congestion in the cove and fjord regions. Remarkably, the aromaticity of these two structural isomers can be tailored by the annulated direction of cyclopenta[b]fluorene units. Isomer 1 (Eoptg = 1.13 eV) behaves as a closed-shell compound with weakly antiaromatic feature, whereas its structural isomer 2 displays a highly stable tetraradical character (y0 = 0.23; y1 = 0.22; t1/2 = 91 days) with a narrow optical energy gap of 0.96 eV. Moreover, the curved PH 2 exhibits remarkable ambipolar charge transport in solution-processed organic thin-film transistors. Our research provides a new insight into the design and synthesis of stable functional curved aromatics with multiradical characters. © The Royal Society of Chemistry.
- ItemTailoring Magnetic Features in Zigzag-Edged Nanographenes by Controlled Diels–Alder Reactions(Weinheim : Wiley-VCH, 2020) Ajayakumar, M.R.; Fu, Yubin; Liu, Fupin; Komber, Hartmut; Tkachova, Valeriya; Xu, Chi; Zhou, Shengqiang; Popov, Alexey A.; Liu, Junzhi; Feng, XinliangNanographenes (NGs) with tunable electronic and magnetic properties have attracted enormous attention in the realm of carbon-based nanoelectronics. In particular, NGs with biradical character at the ground state are promising building units for molecular spintronics. However, most of the biradicaloids are susceptible to oxidation under ambient conditions and photolytic degradation, which hamper their further applications. Herein, we demonstrated the feasibility of tuning the magnetic properties of zigzag-edged NGs in order to enhance their stability via the controlled Diels–Alder reactions of peri-tetracene (4-PA). The unstable 4-PA (y0=0.72; half-life, t1/2=3 h) was transformed into the unprecedented benzo-peri-tetracenes (BPTs) by a one-side Diels–Alder reaction, which featured a biradical character at the ground state (y0=0.60) and exhibited remarkable stability under ambient conditions for several months. In addition, the fully zigzag-edged circumanthracenes (CAs) were achieved by two-fold or stepwise Diels–Alder reactions of 4-PA, in which the magnetic properties could be controlled by employing the corresponding dienophiles. Our work reported herein opens avenues for the synthesis of novel zigzag-edged NGs with tailor-made magnetic properties. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemHelical Nanographenes Containing an Azulene Unit : Synthesis, Crystal Structures, and Properties(Wiley-VCH Verlag, 2019) Ma, Ji; Fu, Yubin; Dmitrieva, Evgenia; Liu, Fupin; Komber, Hartmut; Hennersdorf, Felix; Popov, Alexey A.; Weigand, Jan J.; Liu, Junzhi; Feng, XinliangThree unprecedented helical nanographenes (1, 2, and 3) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps (2: 1.88 eV; 3: 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.