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

Macrocyclic dications 2(2+) composed of two triarylmethylium units were designed and synthesized. In contrast to the reference monocations 1(+), macrocyclic dications 2(2+) 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 2(2+) 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.

Automated summary

Macrocyclic dications 2(2+), composed of two triarylmethylium units, were designed and synthesized. These dications exhibited mechanochromic emission extending to the red region due to their constrained structures and proper counterion choice. The mechanochromic behavior was induced by crystal-to-amorphous transition, and intermolecular interaction played a key role in changing the emission pattern.