Multi-dimensional hydrogen bonds regulated emissions of single-molecule system enabling surficial hydrophobicity/hydrophilicity mapping

Constructing multi-dimensional hydrogen bond (H-bond) regulated single-molecule systems with multi-emission remains a challenge. Herein, we report the design of a new excited-state intramolecular proton transfer (ESIPT) featured chromophore (HBT-DPI) that shows flexible emission tunability via the multi-dimensional regulation of intra- and intermolecular H-bonds. The feature of switchable intramolecular H-bonds is induced via incorporating several hydrogen bond acceptors and donors into one single HBT-DPI molecule, allowing the "turn on/off" of ESIPT process by forming isomers with distinct intramolecular H-bonds configurations. In response to different external H-bonding environments, the obtained four types of crystal/cocrystals vary in the contents of isomers and the molecular packing modes, which are mainly guided by the intermolecular H-bonds, exhibiting non-emissive features or emissions ranging from green to orange. Utilizing the feature of intermolecular H-bond guided molecular packing, we demonstrate the utility of this fluorescent material for visualizing hydrophobic/hydrophilic areas on large-scale heterogeneous surfaces of modified poly(1,1-difluoroethylene) (PVDF) membranes and quantitatively estimating the surface hydrophobicity, providing a new approach for hydrophobicity/hydrophilicity monitoring and measurement. Overall, this study represents a new design strategy for constructing multi-dimensional hydrogen bond regulated ESIPT-based fluorescent materials that enable multiple emissions and unique applications.