Greatly enhanced ultrafast optical absorption nonlinearities of pyridyl perovskite nanocrystals axially modified by star-shaped porphyrins

The long-chain ligands and weak charge-transport capacity of perovskite nanocrystals (NCs) always hinder their optoelectronic applications. Our study proposes an effective strategy to unlock the optimized nonlinear optical (NLO) properties of perovskite via aromatic ligand-exchange plus porphyrin-axial-coordination. The synthesized porphyrin-pyridine dual-modified CsPbBr₃-NC hybrid material, fabricated using 4-(aminomethyl)pyridine (PyMA) and a novel star-shaped zinc-porphyrin trisubstituted triazacoronene compound (ZnPr), exhibits excellent NLO absorption performance under femtosecond (fs) laser irradiation in the visible to near-infrared range. Specifically, its nonlinear absorption coefficient is 10 times higher than that of the pristine CsPbBr₃-NC and it also possesses an outstanding optical limiting (OL) capability with an OL threshold as low as 1.8 mJ cm⁻². The modification of PyMA ligands reduces the trap state density on the perovskite surface and promotes the electronic coupling between the NC lattices. With the aid of PyMA coordinating with the Zn atoms in ZnPr, large-size planar porphyrins are anchored on the perovskite surface from the axial position, which may enhance the ligand protection capability and thereby significantly facilitate the charge transport between porphyrin components and perovskite NCs. The above two-step modification synergistically contributes to the prominent NLO performance. Our work affords a new viable paradigm for developing multi-field and high-performance perovskite NC photonic materials and devices.