Topological and Conformational Effects on Electron Transfer Dynamics in Porphyrin-[60]Fullerene Interlocked Systems

Abstract

The effect of molecular topology, and conformation on the dynamics of photoinduced electron transfer (ET) processes has been studied in interlocked electron donor-acceptor systems, specifically rotaxanes with zinc(II)-tetraphenylporphyrin (ZnP) electron donor and [60]fullerene (C60) as the electron acceptor. Formation or cleavage of coordinative bonds was used to induce major topological and conformational changes in the interlocked architecture. In the first approach, the tweezers-like structure created by the two ZnP stopper groups on the thread was used as a recognition site for complexation of 1,4-diazabicyclo[2.2.2]octane (DABCO), which creates a bridge between the two ZnP moieties on the rotaxane, generating a catenane structure. The photoinduced processes in the DABCO-complexed (ZnP)2-[2]catenate-C60 system were compared with those of the (ZnP)2-rotaxane-C60 precursor and the previously reported ZnP-[2]catenate-C60. Steady-state emission and transient absorption studies showed that a similar multistep ET pathway emerged for rotaxanes and catenanes upon photoexcitation at various wavelengths, ultimately resulting in a long-lived ZnP•+/C60•− charge separated radical pair state. However, the decay kinetics of the latter states clearly reflect the topological differences between the rotaxane, the catenate, and DABCO-complexed-catenate architectures. The lifetime of the long-distance ZnP•+–[Cu(I)phen2]+–C60•− charge separated state is more than four times longer in 3 (1.03 µs) than in 1 (0.24 µs) and approaches that in catenate 2 (1.1 µs). The results clearly showed that adoption of a catenane from a rotaxane topology inhibits the charge recombination process. In a second approach, the Cu(I) ion used as template to assemble the (ZnP)2–[Cu(I)phen2]+–C60 rotaxane was removed, and structural analysis suggested a major topographical change occurred, such that charge separation between the chromophores was no longer observed upon photoexcitation in nonpolar as well as polar solvents. Only ZnP and C60 triplet excited states were observed upon laser excitation. These results highlighted the critical importance of the central Cu(I) ion for long range ET processes in these large interlocked electron donor-acceptor systems.

Photoinduced Electron Transfer Involving a Naphthalimide Chromophore in Switchable and Flexible [2]Rotaxanes

“…[4] For instance, Sauvage and co-workers reported on multiporphyrinic rotaxanes. [5][6][7] C 60 has also been exploited for its photophysical andr edox properties as an electron acceptor in rotaxanes developed by Sauvage et al, [8] Ito et al [9] and Schuster,G uldi et al [10][11][12] Although the high flexibility of such large systems often prevents ac lear interpretation of the results, theses tudies highlight the importance of the mutual arrangement betweent he chromophores in the efficiency of the PET process.…”

Photoinduced Multistep Charge Separation in a Heteroleptic Cu(I) Bis(phenanthroline)-Based Donor–Chromophore–Acceptor Triad

“…20,27,30,32,34 In principle, such bulky substituents can increase the MLCT lifetime and affect the energetics of electron transfer. 20,27,32,34 Despite their similarities to [Ru(bpy) 3 19,32,[35][36][37][38][39][40][41][42][43][44][45][46]31,47 This situation likely arises for two reasons: First, the lability of Cu(I) generally means that an equilibrium mixture of copper complexes exists in solution if multiple similar-type ligands are present, thus complicating any data interpretation. Second, and probably more importantly, the [Cu(II)P 2 ] 2+ product of the initial MLCT oxidative quenching is such a weak oxidant that easily oxidizable donors must be employed.…”

“Click”-reaction: An alternative tool for new architectures of porphyrin based derivatives

“…In conclusion, the triazole ring proved to be an excellent bridge for efficient and rapid electron transfer between the zinc porphyrin and the C 60 moiety. M a n u s c r i p t Tert-butyl porphyrin 3 was used by another group in order to prepare rotaxanes linked to electron donors and C 60 [87,88]. The synthesis of 20 ( The same group synthesized a new class of donor-acceptor catenane containing a diethynyl porphyrin and C 60 [89].…”