A meso-methylsulfanyl-BODIPY derivative (Biellmann BODIPY) underwent Sonogashira-like cross-coupling with terminal alkynes under mild conditions to yield a family of novel fluorescent meso-arylethynyl BODIPYs. These derivatives are characterized by photophysical and computational methods, and some are successfully applied as fluorescent markers for the selective staining of the phytopathogen Clavibacter michiganensis.

Meso-methylsulfanylBODIPY (Biellmann BODIPY) participated in a Sonogashira-like reaction with terminal alkynes, thereby broadening its application as a privileged building block. A series of meso-substituted BODIPYs with arylethynyl groups of different electronic character is prepared (7 new derivatives), as well as a single by-product having a meso-double bond. The photophysical properties of the series are experimentally studied by static and dynamic spectroscopy, and the results are rationalized by theoretical calculations. The molecules with triple bonds present absorption and emission maxima that are redshifted with respect to the derivative with a double bond, and larger fluorescence quantum yields, likely because of lower energy losses due to internal conversion. In particular, the BODIPYs with trimethylsilylethynylene, p-phenoxyphenylethynylene, and p-benzaldehyde exhibited good fluorescence quantum yields and resulted to be soluble in DMSO, for which they are used to stain the phytopathogenic bacterium Clavibacter michiganensis (Cm) that affects tomato crops. Interestingly, the BODIPY bearing the –C≡C–SiMe₃ group does not interact with the bacteria, while for the other two derivatives, the stained Cm are clearly detected by laser scanning microscopy. This likely indicates that aromatic substituents increase the adhesion of the BODIPYs to the wall of Cm.