Synthesis and Photophysical Properties of 3,5-Bis(oxopyridinyl)- and 3,5-Bis(pyridinyloxy)-Substituted Boron-Dipyrromethenes

Nucleophilic substitution reactions of 2-, 3- and 4-hydroxy-pyridines with 3,5-dibromo meso-aryl and meso-furyl boron-dipyrromethenes (BODIPYs) resulted in the formation of the corresponding 3,5-bis(oxopyridinyl)-BODIPYs and 3,5-bis(pyridinyloxy)-BODIPYs in decent yields. The effect of a pyridone versus an oxypyridine at the 3- and 5-positions on the spectral, electrochemical and photophysical properties were studied as a function of solvent. The 3,5-bis(oxopyridinyl)- BODIPYs exhibit broad, red-shifted absorption and emission bands, decreased quantum yields and lifetimes, displayed large Stokes shifts and easier reductions than did the 3,5-bis(pyridinyloxy)-BODIPYs. The differences in the properties of these two classes of BODIPY dyes are attributed to the extension of pi-delocalization associated with the electron-deficient nature of the pyridone groups.