Preprint『チエノシクロペンタ縮環ピレンにおける16π電子反芳香族発現』がChemRxivにて公開されました
Fusion-Number-Dependent Emergence of 16π-Electron Antiaromatic Circuits in Thienocyclopenta-Fused Pyrenes
Kenji Tsukamoto,* Koji Takagi, Yasutomo Segawa*
ChemRxiv 2026 DOI: 10.26434/chemrxiv.15009883/v1
Antiaromatic 4nπ-electron circuits provide a powerful strategy for narrowing the HOMO–LUMO gaps of π-conjugated molecules, yet their contribution is often attenuated or obscured in stable polycyclic frameworks by competing local aromatic stabilization. Here we report a systematic series of thienocyclopenta-fused pyrenes containing one (1TP), two (trans-2TP and cis-2TP), or four (4TP) fused thienocyclopentadiene units, designed to evaluate the stepwise contributions of embedded 16π-electron circuits. The molecules were synthesized through Suzuki–Miyaura coupling followed by palladium-mediated annulation. Notably, 4TP was isolated as an air- and ambient-light-stable green solid, and its structure was confirmed by single-crystal X-ray diffraction. Comparative 1H NMR analysis revealed a progressive upfield shift of diagnostic protons upon increasing the number of fused thienocyclopentadiene units, indicating the emergence and amplification of a paratropic ring-current effect. Theoretical calculations supported the emergence and strengthening of 16π-electron antiaromatic contributions in the two 2TP isomers and 4TP. Frontierorbital calculations and cyclic voltammetry further showed that the LUMO level is substantially stabilized whereas the HOMO level remains nearly unchanged, resulting in a systematic decrease in the HOMO–LUMO gaps. These results establish thienocyclopenta fusion as an effective molecular design strategy for controlling the antiaromatic contribution of 16π-electron circuits within a stable carbon-rich π-framework.
