Photoinduced Electron Transfer and Energy Transfer Processes in a Flexible BODIPY-C₆₀ Dyad

Abstract

A new donor–acceptor dyad composed of a BODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) donor and a fullerene C60 acceptor has been synthesized and characterized. This derivative has been prepared using a clickable fullerene building block that bears an alkyne moiety and a maleimide unit. The post-functionalization of the maleimide group by a BODIPY thiol leads to a BODIPY-C60 dyad, leaving the alkyne moiety for further functional arrangement. On the basis of the combination of semi-empirical and density functional theory (DFT) calculations, spectroelectrochemical experiments, and steady-state and time-resolved spectroscopies, the photophysical properties of this new BODIPY-C60 dyad were thoroughly studied. By using semi-empirical calculations, the equilibrium of three conformations of the BODIPY-C60 dyad has been deduced, and their molecular orbital structures have been analyzed using DFT calculations. Two short fluorescence lifetimes were attributed to two extended conformers displaying variable donor–acceptor distances (17.5 and 20.0 Å). Additionally, the driving force for photoinduced electron transfer from the singlet excited state of BODIPY to the C60 moiety was calculated using redox potentials determined with electrochemical studies. Spectroelectrochemical measurements were also carried out to investigate the absorption profiles of radicals in the BODIPY-C60 dyad in order to assign the transient species in pump–probe experiments. Under selective photoexcitation of the BODIPY moiety, occurrences of both energy and electron transfers were demonstrated for the dyad by femtosecond and nanosecond transient absorption spectroscopies. Photoinduced electron transfer occurs in the folded conformer, while energy transfer is observed in extended conformers.

Tracking Light-Induced Electron Transfer Towards O ₂ in a Hybrid Photoredox-Laccase System

“…In other words, it appears that in the complex the rate of energy transfer is slower than the rate of ET. This situation is reminiscent of a recent observation in a flexible BODIPY-C 60 dyad where photoinduced ET occurs in the folded conformer (R = 8.8 A ˚), whereas energy transfer is observed in extended conformers (R = 17-20 A ˚) (Tran et al, 2020). Similarly, in studies on single-walled carbon nanotubes tethered with porphyrins, excited-state energy transfer was found to be absent in the sample with a short tether (Li et al, 2004).…”

Tracking light-induced electron transfer toward O2 in a hybrid photoredox-laccase system

“…In other words, it appears that in the complex the rate of energy transfer is slower than the rate of ET. This situation is reminiscent of a recent observation in a flexible BODIPY-C 60 dyad where photoinduced ET occurs in the folded conformer (R = 8.8 Å ), whereas energy transfer is observed in extended conformers (R = 17-20 Å ) (Tran et al, 2020). Similarly, in studies on single-walled carbon nanotubes tethered with porphyrins, excited-state energy transfer was found to be absent in the sample with a short tether (Li et al, 2004).…”

Selective population of triplet excited states in heavy-atom-free BODIPY-C60 based molecular assemblies

“…1a). The absorption of (3) This relates to the limited electronic coupling between the BDPs and the fullerene due to the absence of conjugation, as already observed in a similar BDP-C 60 dyad [38].…”