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Thus, much research is directed towards the construction of molecular devices capable of performing the photo-induced splitting of water into hydrogen and oxygen. Whilst the sheer intricacy of such a system renders it impossible to replicate synthetically, it is widely held that it is entirely within our grasp to design artificial PMDs that can successfully duplicate this natural photochemical function. Perhaps the most exquisitely effective PMD in existence is the photosynthetic reaction center, enabling ultra-efficient conversion of light into chemical energy, made possible due to a very controlled process of electron transfer following photosensitization. The most intriguing reason underlying use of complexes in PMDs has stemmed directly from nature. These Photochemical Molecular Devices (PMDs) are providing the bridge between materials and molecules, enabling nanometric machines capable of light-induced functions such as directed electron/energy transfer. For example, metal-centred complexes are used in structurally organized molecular assemblies, yielding supramolecular species capable of performing useful light induced functions. Photo-active molecules can also be used as "building blocks" of much larger molecular structures. For example, these molecules are often capable, in these photosensitized forms, of interacting with or being further influenced by their molecular environment, such as solvents, films, sol-gels or biological molecules, and as such can be designed as effective probes of local molecular environment. Through intricate examination and characterization of transient excited states the photophysical influences of molecular sub-units can be defined, and one can begin to intelligently design more and more effective and efficient photo-active molecules. the molecular processes that ensue as a result of interaction of the complex with photons, such as emission, electron/energy transfer and photochemistry. Photochemically interesting molecules typically exhibit efficient absorption of light, and often consist of individual molecular sub-units, of which the electronic influence on each other can instill some very interesting and useful properties into the overall system, principally interesting photo-induced properties, i.e. on which region of an asymmetric molecule, and in which orbital, does an energetically excited electron reside following photo-excitation) and often to obtain dynamic information which traces the progression through the states, typically ranging from the microsecond to sub-picosecond regime. It is desirable to probe the exact distribution of charge within the relevant excited state(s) (e.g. These extensive families of inorganic compounds have wide applicability in technologies such as photomolecular devices and biological probes. These states are accessed upon absorption of photons and essentially represent higher energy forms of the molecule, differing from the lowest energy ground state in the distribution of electrons and/or nuclear geometry.įor example, it is of fundamental significance to study the excited states of metal-centred complexes and organoporphyrins, both synthetic and naturally occurring. Transient spectroscopy encompasses a powerful set of techniques for probing and characterizing the electronic and structural properties of short-lived excited states (transient states) of photochemically or photophysically relevant molecules. Introduction to Transient Spectroscopy and its Applications