Fusion-Number-Dependent Emergence of 16π-Electron Antiaromatic Circuits in Thienocyclopenta-Fused Pyrenes
- 1Institute for Molecular Science
- 2Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Aichi, Japan, 466-8555
- 3Graduate University for Advanced Studies, SOKENDAI
Abstract
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 1 H 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.
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BibTeX
@misc{tsukamoto2026fusionnumberdependent,
title = {{Fusion-Number-Dependent Emergence of 16π-Electron Antiaromatic Circuits in Thienocyclopenta-Fused Pyrenes}},
author = {Kenji Tsukamoto and Koji Takagi and Yasutomo Segawa},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009883/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009883/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Fusion-Number-Dependent Emergence of 16π-Electron Antiaromatic Circuits in Thienocyclopenta-Fused Pyrenes
AU - Kenji Tsukamoto
AU - Koji Takagi
AU - Yasutomo Segawa
PY - 2026
DA - 2026/10/05
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009883/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009883/v1
AB - 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 1 H 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.
ER -