II. Experimental procedure for small molecule synthesis 1 1 , 2-a 2 , 3 3 , 4 4 , 5-a 4 , 6-a 1 , and 7 5 were synthesized according to the literature and their spectroscopic data were reported in the same literature. Scheme S1. Synthesis of 2 2: Propargyl bromide (80% wt. in toluene, 0.28 ml, 2.60 mmol) was added to DMF solution of 3-a (0.30 g, 1.18 mmol in 4.0 ml), then NaH (60% dispersion in mineral oil, 0.17 g, 2.60 mmol) was added to the mixture at 0 ˚C. After stirring for 5 h at rt, the reaction mixture was quenched with water and the product was extracted with diethyl ether. The organic layer was washed with brine, dried with MgSO4 and concentrated. The product was purified by column chromatography (EtOAc:Hexane=1:5) to afford the

We show that multipodal polycationic receptors function as anion‐responsive light‐emitters in water. Prevailing paradigms utilize rigid holes and cavities for ion recognition. We instead built open amphiphilic scaffolds that trigger polar‐to‐nonpolar environment transitions around cationic fluorophores upon anion complexation. This ion‐pairing and aggregation event produces a dramatic enhancement in the emission intensity, as demonstrated by perchlorate as a non‐spherical hydrophobic anion model. A synergetic interplay of C−H⋅⋅⋅anion hydrogen bonding and tight anion–π+ contacts underpins this supramolecular phenomenon. By changing the aliphatic chain length, we demonstrate that the response profile and threshold of this signaling event can be controlled at the molecular level. With appropriate molecular design, inherently weak, ill‐defined, and non‐directional van der Waals interaction enables selective, sensitive, and tunable recognition in water.