Rational Design of Water‐Soluble Dipyrroethene‐Based Red‐Light Emissive Chromophores for Rapid and Selective Recognition of Serum Albumins

Design and synthesis of water‐soluble π ‐conjugated chromophores are one of the significant challenges due to the intrinsic hydrophobicity of the conjugated frameworks. Consequently, rational molecular design to access novel water‐soluble biologically relevant organic chromophores with red‐to‐NIR emission, large Stokes’ shifts, and good fluorescent quantum yields always attracts significant attention. Here, we establish a straightforward synthetic strategy to access a novel class of water‐soluble red‐light‐emissive (up to 645 nm) cationic dipyridyl dipyrroethene derivatives, achieved through strategic engineering of the ( E )‐dipyrroethene (DPE) core. The X‐ray structures of cationic species 8 revealed a very interesting supramolecular nanoarchitectonics. These sets of molecules are showcasing a fluorescence in both the solid state and solution phase across a wide range of solvents, including water, with a decent fluorescent quantum yield and a large Stokes’ shift. Detailed spectroscopic and computational studies support that the balanced intramolecular charge transfer (ICT) leads to a redshift in its absorption/emission. We further expanded the applicability of the water‐soluble chromophore 10 as a rapid, selective, and effective fluorescent‐turn‐on sensor for recognition of serum albumin proteins with a strong binding constant of 2.7 × 10 6 M –1 . This work provides a fundamental platform for designing robust, bio‐responsive water‐soluble π ‐conjugated systems with tenable structural and electronic properties.