Stabilization of the Charge‐Separated States of Covalently Linked Zinc Porphyrin–Triphenylamine–[60]Fullerene

Abstract

Spectroscopic, redox, computational, and electron transfer reactions of the covalently linked zinc porphyrin-triphenylamine-fulleropyrrolidine system are investigated in solvents of varying polarity. An appreciable interaction between triphenylamine and the porphyrin pi system is revealed by steady-state absorption and emission, redox, and computational studies. Free-energy calculations suggest that the light-induced processes via the singlet-excited porphyrin are exothermic in benzonitrile, dichlorobenzene, toluene, and benzene. The occurrence of fast and efficient charge-separation processes ( approximately 10(12) s(-1)) via the singlet-excited porphyrin is confirmed by femtosecond transient absorption measurements in solvents with dielectric constants ranging from 25.2 (benzonitrile) to 2.2 (benzene). The rates of the charge separation processes are much less solvent-dependent, which suggests that the charge-separation processes occur at the top region of the Marcus parabola. The lifetimes of the singlet radical-ion pair (70-3000 ps at room temperature) decrease substantially in more polar solvents, which suggests that the charge-recombination process is occurring in the Marcus inverted region. Interestingly, by utilizing the nanosecond transient absorption spectral technique we can obtain clear evidence about the existence of triplet radical-ion pairs with relatively long lifetimes of 0.71 mus (in benzonitrile) and 2.2 mus (in o-dichlorobenzene), but not in toluene and benzene due to energetic considerations. From the point of view of mechanistic information, the synthesized zinc porphyrin-triphenylamine-fulleropyrrolidine system has the advantage that both the lifetimes of the singlet and triplet radical-ion pair can be determined.

Electron Transfers in Donor–Acceptor Supramolecular Systems: Highlighting the Dual Donor and Acceptor Role of ZSM-5 Zeolite

“…The fact that the peak of 27 Al is located on the diagonal and there is no cross-peak indicates that the coupling between the unpaired electron and Al atom is low and its coupling mechanism takes place through space via the dipolar interaction. The large contribution of 27 Al masks a possible contribution of 29 Si (I = 1/2), the nuclear resonance frequency of which is 2.9 MHz. On the diagonal, we also observe a low-intensity signal at 1.07 MHz corresponding to the nuclear Larmor frequency of 14 N. The spectrum also shows a pair of ridges in the quadrant (+, +) whose coordinates are (3.9, 8.5) and (8.5, 3.9) MHz.…”

“…Some groups work for example on the synthesis of complex molecular assemblies that involve electron donor and acceptor chromophores. Many variations of these assemblies in solution or involving interfacial systems have been published. ,,,,− Nevertheless, their performance in terms of charge separation does not exceed some microseconds. Another approach is to use the internal volume of porous materials.…”

Excitation energy transfer from non-aggregated molecules to perylenediimide nanoribbons via ionic interactions in water

“…The transient absorption traits of singlet-excited states of ZnTPPSK 4 are similar to those of zinc porphyrin, which were examined extensively in previous studies. [41][42][43][44][45][46] The lifetime of the singlet excited state of ZnTPPSK 4 (s S ) was determined to be 2.3 ns from the decay at 500 nm (inset in Fig. 10).…”

Designing Cascades of Electron Transfer Processes in Multicomponent Graphene Conjugates

“…This approach is similar to that we explored in fullerene‐based electron donor‐acceptor conjugates, which exhibit long‐lived charge‐separated states as the product of a cascade of several charge‐transfer events [32] . In particular, we focused on the synthesis of β‐modified porphyrins, which feature electron‐accepting C 60 [32–34] and/or electron‐donating ferrocenes at the β‐, meso ‐, or 4‐phenyl positions [35–41] . Our past work provided fundamental insights into the unambiguous identification of all the different species that evolve as products of any charge‐transfer reactions, namely charge separation, charge shift, charge recombination, etc.…”