The present invention relates to compounds of formula (A), wherein Z is NR10 or O. These compounds represent novel acridinium and xanthylium salts having an unprecedented substituted heterocyclic core. They are useful as fluorescent dyes or precursors thereof in different applications including various imaging and sensing techniques, and, in particular, as photosensitizers and hereby preferably as photocatalysts. The present invention further relates to processes for preparing the inventive compounds via 1,5-organodimetallic reagents from double directed ortho-metalation reactions or combined halogen-metal exchange/directed ortho-metalation reactions.