Multidimensional Assembly of Polynuclear Osmium–Organic π‐Clusters: Aromatic Synergy‐Driven Enhancement of Third‐Order Nonlinear Optical Responses

ABSTRACT Third‐order nonlinear optical (NLO) materials are critical for applications such as optical limiting, all‐optical switching, and ultrafast photonic devices, yet their performance remains constrained by the intricate balance between electronic delocalization and dimensional synergy. This study demonstrates a multidimensional assembly strategy to engineer aromatic synergy in osmium–organic π‐clusters, achieving unprecedented enhancement of third‐order NLO response. Guided by the concept of metal–organic π‐cluster, we design a prototypical Os 3 ‐plane unit as a foundational building block. Through horizontal covalent extension (C─C bonding) and vertical metallophilic stacking (Os─Os interactions), four hierarchical architectures ( Os 6 ‐prism , Os 6 ‐plane , Os 9 ‐prism , and Os 9 ‐plane ) are constructed, each exhibiting amplified NLO properties. Systematic analysis reveals that horizontal assembly enhances in‐plane π‐conjugation through quasi‐two‐dimensional π‐delocalization, while vertical stacking facilitates interlayer π‐orbital overlap. The novel structure, constructed via a multidimensional assembly strategy, exhibits a narrow HOMO–LUMO gap. The expanded π‐delocalization reduces exciton binding energy, promotes electron delocalization, and consequently yields a stronger third‐order NLO response. The Os 9 ‐plane exhibits excellent third‐order NLO response coefficient ( γ = 2.93 × 10 7 a.u.), which is two orders of magnitude higher than that of the Os 3 ‐plane . This work establishes a paradigm of synergistic integration between multidimensional assembly and aromatic π‐conjugation for enhanced NLO performance, opening new avenues for optoelectronic material design.