Photochemical molecular device

Molecular devices capable of performing light-induced functions (i.e., devices powered by light or capable of elaborating light signals) can be 

Charge Transfer Spectroscopy of Cyano-Bridged Complexes 

---

Balzani, V., L. Moggi, and F. Scandola (1987), Towards a Supramolecular Photochemistry Assembly of Molecular Components to Obtain Photochemical Molecular Devices", in V. Balzani, Ed., Supramolecular Photochemistry, NATO ASI Series, Ser. C, Vol. 214, D. Reidel, Dordrecht, Holland. 

The photosynthetic process thus provides us with an example of a complex, light-powered photochemical molecular device which uses light as an energy supply in order to facilitate energy conversion. In green plants, this molecular device is located within a specially-adapted photosynthetic membrane. 

Adapted from V. Balzani, Photochemical molecular devices , Photochemical and Photobiological Sciences, 2003 (2), 459-476... 

V. Balzani (2003) Photochemical molecular devices, Photochem. Photobiol. Sci., 2 495-476. 

When interaction between the metal-based components is weak, polynuclear transition metal complexes belong to the field of supramolecular chemistry. At the roots of supramolecular chemistry is the concept that supramolecular species have the potential to achieve much more elaborated tasks than simple molecular components while a molecular component can be involved in simple acts, supramolecular species can performIn other words, supramolecular species have the potentiality to behave as molecular devices. Particularly interesting molecular devices are those which use light to achieve their functions. Molecular devices which perform light-induced functions are called photochemical molecular devices (PMD). Luminescent and redox-active polynuclear complexes as those described in this chapter can play a role as PMDs operating by photoinduced energy and electron transfer processes. ... 

Balzani, V., Moggi, L., Scandola, F. (1987) Towards a supramolecular photochemistry assembly of molecular components to obtain photochemical molecular devices in Supramolecular Photochemistry, NATO Advanced Science Institutes Series Series C Mathematical and Physical Sciences (ed. V. Balzani), D. Reidel Publishing Company, Dordrecht, vol. 214, pp. 1-28. 

Fig. 17. Molecular recognition-dependent photochemical molecular devices. Photochemical processes such as energy transfer (ET) or photoinduced electron transfer (PeT) may be induced via association of two (or more) complementary units, each bearing a component of the device the complementary units may be as small as heterocyclic bases or as large as antigen-antibody conjugates.

Fig. 18. Light-conversion photochemical molecular device, consisting of two components, a light collector (or antenna, lightabsorbing groups A) and a light emitter E, and performing a three-step process absorption (A), energy transfer (ET), and emission (E).

Polymetallic complexes presenting directional energy migration are of much significance for the design of photochemical molecular devices. Large arrays of multiple photoactive and redox-active building blocks (of ruthenium- or osmium tris(bipyri-dine)-type for instance) have been constructed for such purposes [A. 10,8.25-8.27]. 

Figure 11.11 (a) Schematic representation of a photochemical molecular device for photoinduced... 

Luminescent and redox-reactive building blocks for the design of photochemical molecular devices mono-, di-,tri-, and tetranuclear ruthenium(n) polypyridine complexes. [G. Denti, S. Campagna, L. Sabatino, S. Serroni, M. Ciano, V. Balzani, Inorg. Chem. 1990, 29(23), 4750-4758] [ 830]. 

Nierengarten J.-F., Eckert J.-F., Felder D., Nicoud J.-F., Armaroli N., Marconi G., Vicinelli V., Boudon C., Gisselbrecht J.-P., Gross M., Hadziioannou G., Krasnikov V., Ouali L., Echegoyen L., Liu S.-G. (2000) Synthrsis and electronic properties of donor-linked fullerenes towards photochemical molecular devices, Carbon, 38, 1587-1598. 

Based on their easily tunable photophysical and redox properties, transition metal complexes are versatile components to be used in the construction of photochemical molecular devices. The studies presented in this article show that the combination of the Ru(bpy)22+ photosensitizer and cyanide bridging units allows the synthesis of a variety of polynuclear systems that exhibit interesting photochemical properties. Depending on the nature of the attached metal-containing units, supramolecular systems can be obtained that undergo efficient photoinduced intramolecular energy or electron transfer processes. 

Aromatic amine complexes65 of osmium, and also complexes of N macrocycles, are generally similar to those of Ru, but [Os(bipy)3]2+ and [Os(terpy)2]2+ are more labile and reactive than their Ru analogues. As for Ru, some Os11 complexes are luminescent and potentially of use in photochemical molecular devices and for detection of DNA.66... 

In general, molecular-level devices that perform light-induced functions, that is, in which photons act as an energy supply and/or input/output signals, can be termed photochemical molecular devices (PMDs) [2, 4, 9]. The role of light in reference to the relevant features of molecular-level devices will be discussed in more detail in the following section. 

Pseudorotaxane species whose components incorporate units capable of exhibiting specific photochemical and/or redox properties are of particular interest for the purpose of constructing photochemical molecular devices. Some examples are reported in Figure 5, namely, a thread (11H+) with an ammonium function and a photoactive anthracene as a... 

Porphyrins, owing to their outstanding photophysical and redox properties [74], are extensively used for the construction of photochemical molecular devices to achieve charge separation over nanometric distance [75]. Porphyrin units have been successfully incorporated into rotaxane structures [76, 77], first playing the role of stoppers. In CHjCN solution at room temperature, [2]rotaxane 17 (Fig. 15) [78, 79] undergoes a very fast (ca. 2 ps) electron transfer process from the Zn(II) to the Au(III) porphyrin upon excitation of the Zn(II) porphyrin moiety (process 1 in Fig. 15). Although direct back electron transfer from the Au(II) to the Zn(III) porphyrin indeed occurs (530 ps), the initial state is restored mainly via oxidation/reduction of the central copper unit, that is, through an electron transfer from... 

---