Unlocking Color-Tunable Pyrene Emissions: Polymorph Engineering and Two-Photon Excited Charge-Transfer Cocrystals

We present a polymorph-based design strategy to modulate the excimer emission in pyrene derivatives by controlling their crystal packing. A simple pyrene molecule, functionalized with an alcohol group, exhibits strikingly different photoluminescence quantum yield (PLQY) depending on its solid-state arrangement. A co-facial π-π stacked polymorph achieves an impressive PLQY of 88%, while an orthogonally packed form shows a much lower efficiency of 14%. Leveraging the intrinsic photophysical richness of the pyrene core, we further construct color-tunable charge transfer (CT) cocrystals by pairing pyrene donors with various electron-accepting moieties. These cocrystals display high emission efficiencies across the visible to near-infrared (NIR) spectrum, enabled by efficient CT interactions and mixed stacking geometries. Notably, emission can be extended into the NIR region by inducing radical formation in the acceptor components. This work highlights the power of crystal engineering in polycyclic aromatic hydrocarbons (PAHs) to create highly emissive materials and offers new prospects for their application in advanced optoelectronic devices, including efficient two-photon emitters.