Preparation and Photophysical Study of Rhodamine-Perylenebisimide Electron Donor-Acceptor Dyad/Triads Containing Flexible Linkers.

We report the synthesis and characterization of the photophysical characterization of a series of rhodamine (Rho)-perylenebisimide (PBI) electron donor-acceptor dyad/triads containing flexible alkyl spacers (ethylene or hexylene chains). Steady-state absorption and emission, femtosecond and nanosecond transient absorption (fs-TA and ns-TA), cyclic voltammetry, triplet-triplet energy transfer (TTET) experiments and DFT/TD-DFT calculations were combined to elucidate the excited-state dynamics. fs-TA spectral study indicates fast decay of the S1 state and formation of the 3PBI state (0.32-663 ps), which is supported by the ns-TA spectra. The localized PBI triplet (3PBI*) exhibits unusually long lifetimes (up to 272 μs) as determined by the TTET experiment. No long-lived charge-separated (CS) state was observed. While a Förster resonance energy transfer (FRET) probably occurs between PBI and the open-ring rhodamine, a photo-induced electron transfer is proposed to be responsible for the quenching of the fluorescence of the PBI moiety.