Combined Experimental and Theoretical Study of Efficient and Ultrafast Energy Transfer in a Molecular Dyad

We have characterized the dynamics and the e ffi ciency of electronic energy transfer (EET) in a newly synthesized molecular dyad, composed of a styryl-pyridinium donor and a BODIPY acceptor. The kinetics of the process has been studied with femtosecond transient absorption spectros- copy in di ff erent solvents. In all the analyzed media EET is quantitative and very fast, as we fi nd that almost 70% of the overall excitation energy is transferred from the donor to the acceptor on a subpicosecond time scale. The experimental measurements have been supported by a theoretical analysis; the electronic couplings between the donor and acceptor moieties have been calculated at the (TD)DFT level and complemented by a conformational analysis of the full dyad. The computed energy transfer times are in good agreement with the experimental values; this allowed us to verify the correctness of the Fo ̈ rster equation, demonstrating that, although EET in the examined system occurs on an ultrafast time scale, the approximations introduced in the case of the weak coupling regime remain valid.