Heterowheel [4]Pseudorotaxane Exhibiting Solid-State Near-Infrared Photochromism, Amine-Selective Vapochromism, and Tunable Fluorescence over a Broad Excitation Range.

The development of simple and efficient methods to construct smart optical materials with dual-mode displays (reflective and emissive modes) is highly desirable yet remains challenging. In this work, we investigated the host-guest binding interactions between two macrocyclic hosts (cucurbit[7]uril (Q[7]) and β-cyclodextrin (β-CD)) and a thiazolothiazole-extended viologen axle (PTV·Cl2). Based on this, we designed and constructed a heterowheel [4]pseudorotaxane (PTV2+@Q[7]·β-CD2) through supramolecular self-assembly. Due to the effective protection of the axle molecule PTV2+ by three macrocycles, the resultant [4]pseudorotaxane exhibited intriguing near-infrared (NIR) photochromism and amine-selective vapochromism, as confirmed by UV-vis diffuse reflectance (DR) and ESR spectroscopy. Moreover, benefiting from the macrocyclic confinement effect, the [4]pseudorotaxane exhibited solid-state fluorescence with a broad excitation range (from 254 to 430 nm). The combination of exceptional stimuli-responsive chromism and strong fluorescence emission renders the [4]pseudorotaxane promising for practical applications in erasable inkless printing and multiple anti-counterfeiting.