Conformationally Locked AIE Chromophores in Organotin Coordination Networks for Enhanced Two‐Photon‐Excited Fluorescence

Efficient two‐photon‐excited fluorescence (TPEF) in crystalline frameworks requires compact, ordered chromophore organization while suppressing nonradiative decay from uncontrolled aggregation. Herein, tetranuclear organotin clusters were used to regulate the spatial arrangement and intramolecular rotation of tetraphenylethylene (TPE) chromophores. Two organotin coordination networks, OCN‐1 and OCN‐2, were synthesized from TPE‐based carboxylate ligands and tetranuclear organotin clusters. OCN‐1 adopts a 3D entangled architecture of interwoven 2D (4, 4)‐grid layers, whereas OCN‐2 comprises densely staggered 1D coordination chains. In both structures, coordination anchoring and short‐range contacts involving adjacent phenyl groups and tin‐bound alkyl substituents restrict aromatic rotation. Consequently, OCN‐1 and OCN‐2 achieved high solid‐state photoluminescence quantum yields (PLQYs) of 92% and 95%, respectively. The hydrophobic organotin internal surface further imparted superhydrophobicity, broad aqueous stability, and negligible PL quenching under high‐humidity. Under 800 nm femtosecond excitation, OCN‐1 exhibited a pronounced TPEF response with an apparent two‐photon absorption cross section ( σ 2 , app) of approximately 4755 GM. In colloidal dispersions, its σ 2 , app was nearly 7.3‐fold higher than that of H 4 ETTC aggregates under identical conditions. These findings establish organotin‐directed chromophore packing as an effective strategy for converting AIE chromophore aggregation into moisture‐resistant crystalline materials with enhanced nonlinear fluorescence.