| Apr 29, 2026 |
New reaction expands the shapes chemists can build from nanographene molecules
Chemists developed an L-APEX reaction that extends polycyclic aromatic hydrocarbons at the previously inaccessible L-region.
(Nanowerk News) A team of Japanese chemists has developed a reaction that selectively extends one of the most chemically stubborn parts of polycyclic aromatic hydrocarbons (PAHs), the carbon ring systems used to build nanographenes. The new method, an Annulative π-Extension (APEX) reaction targeting the L-region, lets chemists design a wider range of organic semiconductors for smartphones, OLED displays, and solar cells.
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The work fills the last unaddressed edge region in nanographene synthesis and was published in Chemical Science ("L-region-selective annulative π-extension through dearomative activation of polycyclic aromatic hydrocarbons").
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Key Findings
- A new L-APEX reaction selectively extends the L-region of PAHs, the last edge region that had resisted controlled extension.
- The three-step sequence runs in a single pot, delivers 45 percent yield, and produces no detectable side products from competing APEX reactions.
- The method can be combined with further L-APEX or K-APEX reactions to build larger and more intricate PAH structures.
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Background on nanographene synthesis
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Nanographenes are organic semiconductor materials that appear in commercial devices including smartphones, OLED displays, and solar cells. At the molecular scale they are PAHs, which are networks of fused benzene rings. The size and shape of each PAH govern how it conducts charge and absorbs light, so chemists routinely tune these molecules' electronic properties by adding extra rings at specific positions on the carbon skeleton.
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The edges of a PAH are not chemically uniform. Depending on local geometry, the peripheral positions are classified as K, M, L, bay, or fissure regions, each with its own reactivity profile. Researchers at Nagoya University previously developed the APEX reaction family, which converts smaller PAHs into larger ones and into nanographenes by adding rings at chosen edge positions. Variants were developed to selectively target most of these regions, but the L-region remained intractable because it is intrinsically more stable and harder to engage.
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How the chemical reaction works
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The new study was led by graduate student Kanami Nakata with Associate Professor Hideto Ito of the Graduate School of Science at Nagoya University and Principal Investigator Kenichiro Itami of RIKEN and the Institute of Transformative Bio-Molecules at Nagoya University. The team adapted an earlier M-APEX reaction reported by Matsuoka and colleagues in Nature Communications in 2021. In that route, the aromatic ring is first broken to make it reactive, then an iron catalyst drives a diarylation step with a Grignard reagent at the M-region.
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The L-APEX reaction begins with the same de-aromatization step but then takes a different chemical route. Once the ring loses its aromaticity, a palladium catalyst carries out an allylic substitution, after which an intramolecular substitution and re-aromatization complete the extension at the L-region. The full three-step sequence runs in one pot and delivers a 45 percent yield with no detectable side products attributable to other APEX reactions.
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The researchers also demonstrated that an L-APEX product can be subjected to a second L-APEX reaction or to a K-APEX reaction, letting several extensions be combined to build large and structurally complex PAHs. With the L-region now accessible alongside the K, M, bay, and fissure regions, chemists have selective access to every peripheral position on these molecular building blocks.
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Selective access to the L-region gives synthetic chemists more control over the size and shape of nanographene molecules, which in turn determines their electronic behavior. The result expands the design space for the organic semiconductors used in displays and solar cells.
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