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Light‐harvesting is a fundamental process in nature, which inspires researchers to develop artificial systems for photocatalysis, photovoltaics, and biosensing. A previously introduced light‐harvesting nanoantenna, based on polymeric nanoparticles (NPs) loaded with rhodamine dyes and bulky hydrophobic counterions, provides a record‐breaking antenna effect ≈1000. However, the high dye cooperativity of its thousands of encapsulated dyes causes energy losses by traces of self‐quenched dye aggregates. Here, it is found that these imperfections can be suppressed by blank hydrophobic salts (BHS) formed by the same bulky counterion (fluorinated tetraphenylborate) with an optically inactive cation, analogs of ionic liquids. The presence of BHS increases twofold the fluorescence quantum yields and fluorescence lifetimes of NPs and suppresses their fluorescence blinking. This study assumes that BHS provides an excess of bulky counterions that excludes traces of dye aggregates. As a result, an efficient Forster resonance energy transfer (FRET) is achieved from 40 000 dye donors to a single acceptor within a 70 nm particle, leading to the antenna effect of 4800, which is by far the highest value reported to date. Using this nanoantenna, a single‐molecule detection of the FRET acceptor is realized at low excitation power using an RGB camera of a smartphone. [ABSTRACT FROM AUTHOR]

Dye‐loaded polymeric nanoparticles emerge as powerful bioimaging tools, but their assembly is challenged by aggregation‐caused quenching (ACQ) of flat fluorophores. Aggregation‐induced emission (AIE) proposes an effective solution against ACQ by exploiting propeller‐shaped neutral fluorophores without polymeric blending. Fighting ACQ of ionic dyes in polymeric nanoparticles can be achieved by bulky hydrophobic counterions. Here, it is aimed to generate an AIE phenomenon in poorly emissive ionic dyes using bulky counterions. Three cationic hemicyanine dyes of styryl pyridinium family are synthesized: two planar fluorophores featuring ACQ and one propeller‐shaped AIE fluorophore. It is found that, in water, bulky fluorinated tetraphenylborates can light up all three dyes, including planar non‐AIE fluorophores. The described "ionic" AIE (iAIE) with bulky counterions enables preparation of 50‐nm dye‐loaded polymeric nanoparticles showing 40% quantum yield at 500 mm dye loading, whereas small anions favor poorly emissive large aggregates. Single‐particle microscopy reveals that these nanoparticles emit without blinking 50‐fold brighter than commercial quantum dots "Qdot 605" (at 470‐nm excitation). iAIE opens the route to assembling charged intrinsically non‐AIE fluorophores into bright fluorescent (nano)materials. [ABSTRACT FROM AUTHOR]