Rotaxanes photoinduced

Rotaxane 316+ was specifically designed36 to achieve photoinduced ring shuttling in solution,37 but it also behaves as an electrochemically driven molecular shuttle. This compound has a modular structure its ring component is the electron donor macrocycle 2, whereas its dumbbell component is made of several covalently linked units. They are a Ru(II) polypyridine complex (P2+), ap-terpheny 1-type rigid spacer... 

Wurpel, G. W. H., Brouwer, A. M., van Stokkum, I. H. M., Farran, A., Leigh, D. A., Enhanced hydrogen bonding induced by optical excitation Unexpected subnanosecond photoinduced dynamics in a peptide-based [2]rotaxane. J. Am. Chem. Soc. 2001, 123, 11327-11328. 

Photoinduced Intramolecular Electron Transfer Within Porphyrinic Rotaxanes... 

In making rotaxanes usable as parts of molecular devices and with the purpose of studying long range election transfer processes within large molecular systems of well controlled geometries, the introduction of photoactive and electroactive compounds has been a valuable development. Photoinduced electron transfer between porphyrin species has a particular relevance to the primary events occurring in bacterial photosynthetic reaction center complexes, and so is a well studied phenomenon. 

The rates of photoinduced electron transfer between the zinc porphyrin and the gold(m) porphyrin are 1.7 ps for the Cu(i)-complexed [2]-rotaxane, and 36 ps for... 

Figure 6.8 Structural formula of the rotaxane 96+ and schematic representation of the intramolecular (below left) and sacrificial (below right) mechanisms for the photoinduced shuttling movement of macrocycle between the two stations A1 and A2.

Keywords Catenane Ir/Ru Light-driven molecular machine Photoinduced Charge Separation Rotaxane Scorpionate... 

Chambron J-C, Collin J-P, Dalbavie JO, et al. Rotaxanes and other transition metal-assembled porphyrin arrays for long-range photoinduced charge separation. Coord Chem Rev 1998 178-180 1299-312. 

Kinetic studies have demonstrated that photo-induced electron transfer between the zinc and the gold porphyrin occurs at a rate of (1.7 ps)-1 in Cu(I)-complexed [2]-rotaxane 102, which is much higher than in the case of the free rotaxane 107 (36 ps)-1.73 The higher photoinduced electron transfer rate in the Cu(I) complex 102 than in the demetallated system 107 was explained also in terms of a superexchange mechanism. 

Porphyrinic Rotaxanes Control of the Photoinduced Electron Transfer Rate between PZn and PAu by the Assembler Metal... 

For the copper-free [2]rotaxane the rate of photoinduced electron transfer from the Zn porphyrin excited state to the Au porphyrin is 273 x 10 s (as calculated from Ref. [76c]), which compares well with A i4 = 178 x 10 s. ... 

As in the past two years, fullerenes continue to be a source of considerable photochemical interest and photoinduced electron transfer is a central theme of numerous studies. The field of molecular-scale electronic devices continues to promote interest in the photophysical properties of novel molecular architectures and such aspects of photoactive rotaxanes and catenates have been reviewed (Benniston and Chambron et ai), while Harriman and Ziessel have outlined the design principles associated with the construction of photo-activated molecular wires. 

Figure 15. Photoinduced electron transfer processes that take place in [2]rotaxane 17 + [78, 79].

Figure 16. Photoinduced energy and electron transfer processes occurring in [2]rotaxane 18 + [81], which behaves as a triad for photoinduced charge separation according to the scheme illustrated in Figure 14a. For more details, see text.

Figure 26. Photoinduced shuttling, based on the use of an oxidant scavenger (p-nitrobenzylbromide), of the macrocyclic component in the copper-containing [2]rotaxane 28+ [114],...

For space reasons, in this chapter we will only review recent advances in the field of molecular-level machines operating by means of photoinduced electron-transfer processes. Since such machines are based on pseudorotax-anes, rotaxanes, and catenanes, we will first recall some important features of these kinds of supramolecular systems. 

For the sake of space, in this chapter we will only discuss examples of molecular-level machines based on photoinduced electron transfer processes. An extensive review on artificial molecular machines [3c] and more detailed discussions on electron-transfer processes involving pseudorotaxanes [23a], and rotaxanes and catenanes [23b] are reported elsewhere. 

In order to achieve photoinduced shuttling, the carefully designed rotaxane shown in the top of Fig. 13 has been recently synthesized [7f]. This compound is made of the electron-donor macrocycle R and a dumbbell-shaped component which contains... 

The structure of the rotaxane was characterized by mass spectrometry and NMR spectroscopy, which also established, along with cyclic voltammetry, that the stable translational isomer is the one in which the R component encircles the Ai unit, in keeping with the fact that this station is a better electron acceptor than the other one. The electrochemical, photophysical, and photochemical (under continuous and pulsed excitation) properties of the [2] rotaxane, its dumbbell-shaped component, and some model compounds containing electro- and photoactive units (Fig. 13) were investigated. In an attempt to obtain the photoinduced abacus-like movement of the R macrocycle between the two stations A, and A2, two strategies were devised one was fully based on processes involving only the rotaxane components (intramolecular mechanism), while the other one required the help of external reactants (sacrificial mechanism). 

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