Artificial Photochemical Devices and Machines

Abstract

The interaction between light and matter lies at the heart of the most important processes of life [1]. Photons are exploited by natural systems as both quanta of energy and elements of information. Light constitutes an energy source and is consumed (or, more precisely, converted) in large amount in the natural photosynthetic process, whereas it plays the role of a signal in vision-related processes, where the energy used to run the operation is biological in nature.A variety of functions can also be obtained from the interaction between light and matter in artificial systems [2]. The type and utility of such functions depend on the degree of complexity and organization of the chemical systems that receive and process the photons.About 20 years ago, in the frame of research on supramolecular chemistry, the idea began to arise [3][4][5] that the concept of macroscopic device and machine can be transferred to the molecular level. In short, a molecular device can be defined [6] as an assembly of a discrete number of molecular components designed to perform a function under appropriate external stimulation. A molecular machine [6-8] is a particular type of device where the function is achieved through the mechanical movements of its molecular components.In analogy with their macroscopic counterparts, molecular devices and machines need energy to operate and signal to communicate with the operator. Light provides an answer to this dual requirement. Indeed, a great number of molecular devices and machines are powered by light-induced processes and light can also be useful to read the state of the system and thus to control and monitor its operation. Before illustrating examples of artificial photochemical molecular devices and machines, it is worthwhile recalling a few basic aspects of the interaction between molecular and supramolecular systems and light. For a more detailed discussion, books [9][10][11][12][13][14][15] can be consulted.

Electron Transfer Studies of High Potential Zinc Porphyrin–Fullerene Supramolecular Dyads

“…In Table , dyads with high oxidation potentials for (F 20 TPP)Zn and ((CF 3 ) 4 TPP)Zn achieve rapid CS and CR processes, forming high potential radical ion-pair (RIPs) ([(F 20 TPP)Zn] •+ ←ImC 60 •– and [((CF 3 ) 4 TPP)Zn] •+ ←ImC 60 •– ), which can be applied to ultrafast photoelectronic devices. − Another potential use of the high potential RIPs involves electron mediating to produce one or multi-electron transfer products typically needed for a photocatalytic system. ,, Currently we are exploring such possibilities.…”

“…The reaction center, effectively coupled to the antenna, receives the excitation energy and converts it to chemical energy in the form of trans-membrane charge separation via a multistep electron-transfer process. The stored energy in the form of charge-separated species (electrochemical energy) is later converted into other forms of biologically useful energy such as proton motive force. − Research in designing donor–acceptor hybrid systems mimicking these features of natural and bacterial photosynthesis holds promise not only in designing efficient solar cells in light energy conversion − but also in optoelectronics, molecular wires and switches, and bioenergetics. − …”

New Photophysical Insights in Noncovalent Interaction between Fulleropyrrolidine and a Series of Zincphthalocyanines

“…Natural photosynthesis processes which rely on highly organized supramolecular assemblies have inspired chemists to mimic many aspects on successful energy transmuting process in laboratory scale. Several molecular and supramolecular systems have been elegantly designed in this connection and studied with an emphasis on generating long-lived charge separated states through a charge migration route. − Studies on donor–acceptor dyads capable of mimicking light-induced electron or energy transfer process(s) are of current interest, mainly due to the development of artificial photosynthetic systems, − and also to develop molecular optoelectronic logic gates and devices . After the initial discovery in 1984, the fortuitous contemporary growth of two apparently independent research lines, namely, synthetic fullerene chemistry and supramolecular fullerene photochemistry, has been reciprocally beneficial and contributed to boost activity in both fields.…”

Photochemical Charge Separation in Supramolecular Phthalocyanine−Multifullerene Conjugates Assembled by Crown Ether-Alkyl Ammonium Cation Interactions

“…Study of photoinduced electron-transfer processes in donor−acceptor dyads and polyads is a topic of current interest mainly to develop artificial photosynthetic systems for light-energy harvesting − and also to develop molecular optoelectronic logic gates and devices . Porphyrins and phthalocyanines have been widely utilized in the construction of such dyads as electron donors owing to their rich and well-understood electrochemical and photochemical properties.…”