Synthesis of bisisoindolomethene dyes bearing anisole or ethylthiophene residues for red and near-IR fluorescence

New difluorobora-diisoindolomethenes dyes were synthesized from carbohydrazide and o-hydroxy-acetophenone derivatives bearing phenyl, p-anisole or ethylthiophene substituents. The nature of the substituents allows modulating the fluorescence from 650 nm to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl residues is feasible using Grignard reagents. Standard fluorescence studies prove that very efficient energy transfer, from the pyrene moiety linked to the boron center to the boradiazaindacene, is effective in providing large virtual Stokes shifts.