Modulation of singlet oxygen generation in halogenated BODIPY dyes by substitution at their meso position: towards a solvent-independent standard in the vis region

A series of halogenated BODIPY with different substitutions patterns at meso position such as aryl groups and heteroatoms (methylthio (MeS) and amino (NR2) groups) with various electron-donor and electron-withdrawing properties are studied. A detailed analysis of their photophysical properties as well as a thorough determination of their singlet oxygen quantum yields enlightens the role of the substituents at the meso position. Importantly, one of the new halogenated BODIPY with a methylthio group at the meso position, with intense absorption band in the visible region is proposed as a suitable reference with high singlet oxygen quantum yield, practically constant in different solvents of a wide polarity range.