Energy-Transfer and Charge-Transfer Dynamics in Highly Fluorescent Naphthalimide-BODIPY Dyads: Effect of BODIPY Orientation

We report evidence for photoinduced energy transfer from the naphthalimide (NI) to the BODIPY in NI-BODIPY dyads. Three dyads (1a, 1b, and 1c) were investigated, characterized by different positions of attachment of the BODIPY to the conjugated bridge (meso-, beta-, and alpha-). The time-resolved spectroscopic results showed that the intramolecular energy-transfer rate is enhanced for the dyads characterized by the unusual (1b) and alpha- (1c) with respect to the largely employed meso- (1a) substitution. All of the dyads were strongly fluorescent. Fluorescence quantum yields and lifetimes were interestingly enhanced in the dyads with respect to the monomers (NI and BODIPY). These properties together with their two-photon absorption ability make these bichromophoric systems excellent candidates as fluorescent probes for bioimaging. In the beta-substituted dyad, intramolecular charge transfer takes place following energy transfer. The concerted energy- and charge-transfer dynamics is appealing for solar energy conversion to electricity. Our findings represent a step forward in structure properties understanding and may guide the design of most efficient BODIPY-containing dyads.