Neutral BODIPY derivatives as photosensitizers

A series of 2,6-dibromo-, 2,6-diiodo-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, together with the 4,4-dicyano analogs were synthesized. The photostability of these BODIPY derivatives and their efficiencies in generating singlet oxygen species were determined. Among these, 2,6-dibromo-4,4-dicyano-4-bora-3a,4a-diaza-s-indacene (BODIPY 6) was found to be similarly photostable as Rose Bengal, while 2,6-diiodo-8-iodomethyl-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY 10) and 1,3,5,7,8-pentamethyl-2,6-diiodo-4,4-dicyano-4-bora-3a,4a-diaza-s-indacene (BODIPY 5) were found to be the least stable. For the ability to generate singlet oxygen species, 2,6-dibromo- (BODIPY 3) and 2,6-diiodo-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY 2) were found to be more efficient than Rose Bengal, while BODIPY 10 and 1,3,5,7,8-pentamethyl-2,6-diiodo-4,4-dicyano-4-bora-3a,4a-diaza-s-indacene (BODIPY 5) were quite poor photosensitizers. When Bacillus subtilus cultures were supplemented with the photosensitizers and exposed to light, it was found that the presence of a positive charge in the photosensitizers was essential in order for them to be effective bacterialcidal agents.