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 (g_lum), 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.