Distinct Nanohoop Structures and Ratiometric Emissions of Isomeric DPAC-Based Macrocycles Tuned by Nano-Twisting of Stiff-Stilbene Optical-Switches.

To investigate the manipulations of light on distinct vibration-induced emission (VIE) behaviors, the classic VIE-fluorophore 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) was integrated with an optical switchable stiff-stilbene moiety into the first molecular design of various sized nanohoop structures (i.e., RnD, where n = 4 and 6 with different cavities). The goal is to exploit tunable nano-twisted structures of novel geometric macrocycle isomers, controlled by cis/trans isomerizations of stiff-stilbene units under 320/385 nm light irradiations, to modulate corresponding bent and planar configurational structures of DPAC moieties and adjust their ratiometric (photoluminescence) PL emissions. Light-controllable cis/trans isomerizations of different sized nanohoop structures resulted in distinct emission changes due to adaptable structural constraints, facilitating alterations of PL emission colors with significant Stokes shifts. The emission spectra spanned from cyan/white/orange-light emissions, triggered by cis/trans isomerizations of stiff-stilbene units upon respective light exposures of 320/385 nm. Additionally, external factors such as solvent polarities, viscosities, temperatures, and water contents could further regulate ratiometric emission features of DPAC-based geometric macrocycle isomers, demonstrating high sensitivities toward various environmental changes. This study highlighted the potentials for developing multi-color emissive smart materials by utilizing nano-twisting of DPAC-based nanohoop structures tuned by optical switchable moieties, opening new avenues for innovative applications in stimuli-responsive materials.