Effects of phosphorus(V)-substituted 1,3,4-thiadiazoles on the electronic properties of BODIPY fluorophores

Phosphoryl-substituted fluorophores are of particular importance due to their outstanding photophysical properties, enabling the design of advanced fluorogenic materials for various applications. This study reports the synthesis and characterization of novel BODIPY derivatives functionalized with phosphorus(V)-substituted thiadiazole moieties at the 2- or 2,6-positions of the fluorophore core. Derivatives bearing phosphine oxide and phosphoramide groups were synthesized by the oxidative cyclization of corresponding formyl-BODIPYs with phosphorylthioformic acid hydrazides. The photophysical properties of the dyes were found to be tuned by changing a phosphoryl substituent and the number of heterocyclic moieties. All the dyes are highly fluorescent with quantum yields of up to 99%, along with bathochromic shifts in the absorption and emission maxima, which are most pronounced for 2,6-bis-substituted BODIPYs. Phosphine oxide-substituted BODIPYs were found to be electrochemically active and nontoxic. To sum up, the presence of phosphorus(V)-substituted 1,3,4-thiadiazoles significantly alters the electronic properties of BODIPY fluorophores, as reflected in their spectral, photophysical, and electrochemical properties.