Beyond Excimer: Engineering Pyrene Stacking With Mechanical Bonds for Tunable Emissions.

Aiming to deepen the fundamental understanding of how hierarchical molecular packing governs the overall photophysical properties in multi-chromophore systems, engineering pyrene stacking with mechanical bonds has been successfully realized, leading to the construction of a novel family of pyrene-functionalized [1]rotaxanes, particularly ones with tunable triple-layered pyrene stacking. The precisely controlled pyrene excimer conformations in these structures enable adjustable photophysical behaviors, particularly in circularly polarized luminescence (CPL), including tunable luminescence dissymmetry factors (glum), invertible handedness, and programmable emission wavelengths. Notably, introducing a third pyrene unit into tris-pyrene-functionalized [1]rotaxanes further modulates CPL properties through synergistic or antagonistic interactions, as further confirmed by time-dependent density functional theory (TD-DFT) simulations, revealing a previously unobserved stacking effect. This correlation between spatial stacking and photophysical response not only provides more in-depth fundamental insights for pyrene excimer emissions but also offers critical design principles for developing advanced chiral luminescent materials.