Rotaxane photoactive

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. 

In other studies, the above research group synthesised a number of related one-and two-station, photoactive [2]-rotaxanes incorporating either ferrocene or anthracene stoppers or a combination of each type. In these systems, the terminal stoppers associate with the exterior of the bis(4-4 -bipyridinium)cyclophane tetracation via 7U-stacking. Such proximity has obvious implications for the required rapid electron-transfer to a terminal (ferrocenyl) group in order to be competitive with the simple charge recombination process discussed previously. The relationship between the photoactivity, electron-transfer behaviour and concomitant configurational charges in the above systems has now been described in some detail. " ... 

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. 

Topics of relevance to the content of this chapter which have been reviewed during the year include photoactive [2]rotaxanes and [2]catenanes, photochemical synthesis of macrocycles, phototransformations of phthalimido amino acids, photoaddition reactions of amines with aryl alkenes and arenes, photoreactions between arenenitriles and benzylic donors, photostability of drugs, polycyclic heterocycles from aryl- and heteroaryl-2-propenoic acids, photoreactions of pyrroles, photoamination reactions in heterocyclic synthesis, switching of chirality by light, photochromic diarylethenes for molecular photoionics and solid state bimolecular photoreactions. 

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). 

Abstract The approach based on the copper(I)-templated synthesis of porphyrin catenanes and rotaxanes developed by the authors group is here reviewed. Zn(II) porphyrins and gold(III) porphyrins were chosen as electron donors and electron acceptors, respectively, to constitute the electro- and photoactive parts of the present systems. The processes—energy and electron transfer reactions—occiuring in the interlocked structures upon light absorption in the presence or absence of Cu(I) are presented, their rates and efficiencies critically compared and discussed with respect to properties of the components and of the ensemble. A detailed examination of differences and analogies in photoreactivity between the present and closely related systems reported by others is presented. 

An intriguing series of electro- and photoactive porphyrin catenanes and rotaxanes, obtained by the authors through copper(I)-templated synthesis, is reviewed in the sixth chapter by Lucia Flamigni, Valerie Heitz, and Jean-Pierre Sauvage. The photo-induced processes - energy and electron transfer reactions - occurring in the interlocked structures upon light absorption are discussed in detail and critically compared to closely related systems reported by others. 

Another recent example using PET reaction-based molecular shuttle has also been designed with a CBPQT-based rotaxane, with the thread composed of a porphyrin (Por) as the photoactive unit, Ceo as the electron acceptor, tetrathiafiilvalene (TTF) and dioxynaphthalene as the two tt-electron-donating stations, and substituted 2,6-diisopropylbenzene as the stopper (Figure 36). ° In... 

A monolayer of the photoactive rotaxane trans-31 (Figure 19), which consists of a ferrocene-functionalized -cyclodextrin (/i-CD) macrocycle threaded on a molecnle containing a photoisomerizable azobenzene nnity and a long... 

Rotaxanes endowed with fullerenes are ciurently receiving a lot of attention as a consequence of the bulky nature of the C o molecule, able to act as a stopper, as well as for its unique electrochemical and photochemical properties. Thus, a novel [2]rotaxane has been synthesized in which the Ceo unit behaves as both a stopper and a photoactive unit, as shown in Figure 1. 

---