C₁ symmetric dual-carboxyl-functionalized BODIPY dye: Synthesis photophysical properties, and self-assembly behavior via hydrogen bonding

A BODIPY derivatives 3 with phenylethynyl bridging two carboxyl groups was synthesized via Sonogashira crosscoupling reaction. The structure was characterized by H-1 NMR and HRMS. Its photophysical properties and aggregation behavior in solution were studied by UV-Vis absorption and fluorescence spectroscopy. The compound 3 displays strong absorption and high fluorescence quantum yield. The investigations of UV-Vis and emission also revealed the formation of self-assembled structures in the solid state or liquid/state with translationally slipped pi-stacks of BODIPY units driven by hydrogen bonding between the carboxyl groups. The thermodynamic properties of the BODIPY derivative were carried out by DSC and TGA, indicating it possesses high thermal stability. In addition, the self-assembly of the BODIPY derivative functionalized with two carboxyl groups was explicitly investigated by using scanning tunneling microscopy (STM). The highly ordered supramolecular selfassembly monolayers endow the novel carboxyl functionalized BODIPY with good potential for application in organic devices.