Materials Advances, vol.3, no.1, pp.547-553, 2022 (ESCI)
© 2021 The Royal Society of Chemistry.Organic luminescent compounds with high emission properties play a crucial role in fluorescence labelling and optoelectronic devices. In this work, we prepared three water soluble BODIPY derivatives (B-4, B-5, and B-6) which are weakly fluorescent due to non-radiative relaxation pathways (charge transfer: CT or heavy atom effect). However, CB significantly improves BODIPY fluorescence by ∼10 fold for B-4, and by ∼3 fold for B-5. The (TD)DFT analyses suggest that for B-4 and B-5, the CT state is blue-shifted as a result of the external binding of CB near the pyridinium groups. This effect favoured a radiative decay through a locally-excited (LE) π→π∗ transition state of BODIPYs resulting in a CB-induced emission increase in solution (and in the solid state), without compromising singlet-to-triplet intersystem crossing (ISC). The improved emission of the BODIPY·CB complexes was used for the fluorescence imaging of U87 cells illustrating the relevance of this approach. These results suggest that BODIPY·CB complexes could be used as theragnostic agents by combining fluorescence imaging and treatment by photodynamic therapy.