Bis(triarylmethylium)‐type Macrocyclic Dications: Mechanochromic Emission Extending to the Red Region

Abstract

Macrocyclic dications 22+ composed of two triarylmethylium units were designed and synthesized. In contrast to the reference monocations 1+, macrocyclic dications 22+ exhibited mechanochromic emission extending to the red region (−900 nm), since the luminescence color in a solid state can reversibly change due to their constrained structures granted by alkylene linkers and the choice of a proper counterion. X‐ray diffraction and spectroscopic analyses revealed that such mechanochromic behavior was induced by the crystal‐to‐amorphous transition. A change in the intermolecular interaction of macrocyclic dications 22+ would be the key to realizing a change in the emission pattern, since the color of the molecules did not change by applying mechanical stimuli. These findings may suggest a design strategy for creating a variety of stimuli‐responsive materials, especially for carbocation‐based fluorescent materials.

Cation-Stacking Approach Enabling Interconversion between Bis(xanthylium) and Its Reduced Species

“…Considering that cation units must undergo simultaneous two-electron (2e)reduction at a potential similar to that of monocations 1 + (E 1 red /V vs. SCE: −0.25 for 1a + , −0.15 for 1b + , https://doi.org/10.26434/chemrxiv-2024-fd9ws ORCID: https://orcid.org/0000-0001-7961-3595 Content not peer-reviewed by ChemRxiv. License: CC BY 4.0 and −0.34 for 1c + ) when there is no interaction between the cation units, [37] the stepwise reduction processes indicate that the cation units are close enough to interact with each other even in solution. In addition, unlike with monocations 1 + which exhibit an irreversible process, reversible redox waves were observed for dications 2 2+ , indicating that the cyclophane structure can stabilize both radical cation and biradical species.…”