Efficient Energy Transfer in a Rylene Imide-Based Heterodimer: The Role of Intramolecular Electronic Coupling

The development of antenna molecules with simplified structures can effectively avoid the complex exciton dynamics resulting from conformational mobility. Two distinct heterodimers TP and TBP comprising a perylenediimide (PDI) donor and terrylenediimide (TDI) acting as an energy sink were investigated. Tuned by varying functionalization positions, the bay-to-bay-linked TP offers a strong chromophore coupling, while the bay-to-N-linked TBP exhibits a weak chromophore coupling. Using transient absorption spectroscopy, we found that TP underwent ultrafast vibrational relaxation (τ_VR < 400 fs) from upper vibrational energy levels of the singlet states after pumping at 490 nm, and followed by electron transfer (ET, τ_ET = 2.5 ps) from TDI to PDI. TBP exhibited ultrafast excitation energy transfer (EET, τ_EET = 0.48 ± 0.1 ps) from the excited PDI donor to TDI acceptor, and the subsequent charge transfer (CT) process was almost quenched. This result provides insight into designing novel small molecules capable of efficient energy transfer.