Ion Pair−π Interactions

Fujisawa, Kaori; Humbert-Droz, Marie; Letrun, Romain; Vauthey, Eric; Wesolowski, Tomasz Adam; Sakai, Naomi; Matile, Stefan

doi:10.1021/jacs.5b05593

Scientific article

English

Ion Pair−π Interactions

Contributors

Fujisawa, Kaori; Humbert-Droz, Marie; Letrun, Romain; Vauthey, Eric

; Wesolowski, Tomasz Adam; Sakai, Naomi

; Matile, Stefan

Published in

Journal of the American Chemical Society, vol. 137, no. 34, p. 11047-11056

Publication date

2015

Abstract

We report that anion−π and cation−π interactions can occur on the same aromatic surface. Interactions of this type are referred to as ion pair−π interactions. Their existence, nature, and significance are elaborated in the context of spectral tuning, ion binding in solution, and activation of cell-penetrating peptides. The origin of spectral tuning by ion pair−π interactions is unraveled with energy-minimized excited-state structures: The solvent- and pH-independent red shift of absorption and emission of push–pull fluorophores originates from antiparallel ion pair−π attraction to their polarized excited state. In contrast, the complementary parallel ion pair−π repulsion is spectroscopically irrelevant, in part because of charge neutralization by intriguing proton and electron transfers on excited push–pull surfaces. With time-resolved fluorescence measurements, very important differences between antiparallel and parallel ion pair−π interactions are identified and quantitatively dissected from interference by aggregation and ion pair dissociation. Contributions from hydrogen bonding, proton transfer, π–π interactions, chromophore twisting, ion pairing, and self-assembly are systematically addressed and eliminated by concise structural modifications. Ion-exchange studies in solution, activation of cell-penetrating peptides in vesicles, and computational analysis all imply that the situation in the ground state is complementary to spectral tuning in the excited state; i.e., parallel rather than antiparallel ion pair−π interactions are preferred, despite repulsion from the push–pull dipole. The overall quite complete picture of ion pair−π interactions provided by these remarkably coherent yet complex results is expected to attract attention throughout the multiple disciplines of chemistry involved.

UNIGE affiliation entities

Citation (ISO format)

FUJISAWA, Kaori et al. Ion Pair−π Interactions. In: Journal of the American Chemical Society, 2015, vol. 137, n° 34, p. 11047–11056. doi: 10.1021/jacs.5b05593

Article (Published version)

Article (Accepted version)

OA OTHER

Identifiers

PID : unige:75003
DOI : 10.1021/jacs.5b05593

Journal ISSN

0002-7863

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Creation

02/09/2015 10:21:00

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02/09/2015 10:21:00

Update

13/10/2025 21:16:07

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14/03/2023 23:35:45

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16/02/2026 06:57:26

Ion Pair−π Interactions

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Published in

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Abstract

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Citation (ISO format)

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First validation

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