Energy Transfer in Aminonaphthalimide-Boron-Dipyrromethene (BODIPY) Dyads upon One- and Two-Photon Excitation: Applications for Cellular Imaging

Aminonaphthalimide–BODIPY energy transfer cassettes were found to show very fast (kEET≈1010–1011 s−1) and efficient BODIPY fluorescence sensitization. This was observed upon one‐ and two‐photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two‐photon absorption cross‐section δ of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [δ≈10 GM for the BODIPY versus 19–26 GM in the dyad at λexc=840 nm; 1 GM (Goeppert–Mayer unit)=10−50 cm4 s molecule−1 photon−1]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfer cassette concept, was demonstrated by time‐dependent density functional theory calculations. The applicability of the new probes in the one‐ and two‐photon excitation mode was demonstrated in a proof‐of‐principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY‐containing dyad. Take two: Aminonaphthalimide–BODIPY energy transfer cassettes were designed in order to take advantage for bioimaging from one‐ and two‐photon excitation coupled with energy transfer. The bichromophoric dyads showed ultrafast and highly efficient energy transfer and were used for confocal fluorescence microscopy imaging of HeLa cells as bio‐relevant models.