Photochemistry of supramolecular systems and nanostructured assemblies. In memory of Professor Nick Turro (1938–2012)

Alberto Credi

Alberto Credi (born 1970) received his Laurea from the University of Bologna where, after a research period in the United States, he also earned his PhD in 1999. He is currently Associate Professor of Chemistry at his Alma Mater. His research is focused on the spectroscopy, photochemistry and electrochemistry of molecular and supramolecular species, coordination compounds, and nanoparticles, with the purpose of developing nanoscale devices and machines. Among his scientific awards are the IUPAC Prize for young chemists and the Grammaticakis-Neumann award for photochemistry. He has published 230 articles, reviews and book chapters (h = 51). He is co-author of two monographs on molecular devices and machines and a handbook of photochemistry, and co-editor of a book on electroactive supramolecular systems. He has been invited to speak at more than 100 conferences, Universities and research centres, and he is a member of several professional associations, scientific committees of meetings and advisory boards of journals.

Photochemistry is an important branch of modern science at the crossroads of chemistry, physics, and biology, with implications in the fields of engineering and medicine. It encompasses phenomena which are of the utmost relevance both for living organisms and for technology. Research on biological systems in the past four decades has shown magnificently that the value of the function that can be obtained from the interaction between light and matter is highly dependent on the degree of organization and complexity of the matter that has to receive and process the photons. In the same period ‘the chemistry beyond the molecule’ – that is, supramolecular chemistry – moved its first steps and rapidly established itself as one of the most flourishing areas of chemical sciences. The idea began to arise that molecules might be used as building blocks for the assembly of multicomponent materials and nanoscale devices exhibiting novel and valuable functionalities. In more recent times, the set of components that may be used to assemble new systems and materials by a bottom-up approach has been further extended, owing to the progress in the synthesis and characterization of nanoscale crystals of various sizes and shapes, tubes, wires, ribbons, capsules, graphene derivatives, monolayers, and so on.

It is not surprising, therefore, that the marriage of photochemistry with supramolecular chemistry and, in a more general view, with nanostructured assemblies has been attracting the interest of many scientists, leading to outstanding research achievements that may enable innovative solutions for current pressing problems related to energy, environment, sustainability, and health. Indeed, the ability to control the structure of matter at the molecular level – that is, at the nanoscale – together with the development of new concepts and tools (for example, spectroscopy and microscopy pushed to an extreme resolution in time and space) can open new and unconventional scenarios for the light–matter interaction.

The aim of this themed issue is to gather together the recent advances in photochemistry at its frontiers with supramolecular chemistry, materials science, and biochemistry, taking advantage from the contributions of prominent scientists in their respective areas. A number of tutorial reviews, clustered together in the first part of the issue, will illustrate the basic concepts of supramolecular (multicomponent) photochemistry, and the application of photochemical methods to organized molecular assemblies. Other reviews on both fundamental and applicative aspects related to the interaction of light with organized matter will not only attract the interest of specialists but also further stimulate the curiosity of students and researchers interested to learn more about this fascinating subject.

The basic aspects of light-induced processes for ‘writing’ and ‘reading’ onto chemical species and their exploitation for the design of supramolecular systems that can process photons to obtain functions are discussed by Ceroni, Credi and Venturi (DOI: 10.1039/c3cs60400d). In her tutorial review (DOI: 10.1039/c3cs60352k) Bohne highlights the importance of kinetic experiments to gain mechanistic information on host–guest binding dynamics that cannot be uncovered from thermodynamic studies. Natali, Campagna and Scandola (DOI: 10.1039/c3cs60463b) deal with photoinduced electron transfer mechanisms in modular donor–bridge–acceptor arrays and examine the complex role of the molecular bridge. The tutorial review of Olivucci and co-workers (DOI: 10.1039/c4cs00037d) shows how the concepts and tools of computational photochemistry can be applied to understand the operation of biological as well as artificial supramolecular constructs.

Supramolecular photocatalysis – that is, the combination of confinement effects and non-covalent interactions to control the course of photochemical reactions in terms of efficiency and regio- and/or stereoselectivity – is a subject of high scientific interest with a significant potential for applications in synthetic chemistry and materials science. The topic is presented in the tutorial review of Sivaguru and Vallavoju (DOI: 10.1039/c3cs60471c), and deepened with a multitude of fascinating examples in the articles of Bassani and co-workers (DOI: 10.1039/c3cs60366k) and of Yang and Inoue (DOI: 10.1039/c3cs60339c).

The development of multicomponent structures, spanning from self-assembled aggregates to covalently linked arrays, capable of elaborating photonic signals in a predetermined manner is crucial for the realization of optoelectronic materials and devices, some of which – for example LEDs and organic solar cells – have already started to change our everyday life. Recent progress on oligo(phenylenevinylene)-type systems and on architectures resulting from hierarchical self-assembly are respectively reviewed in the contributions of Praveen, Ajayaghosh, Armaroli and co-workers (DOI: 10.1039/c3cs60406c) and of Ma, Zhao and co-workers (DOI: 10.1039/c3cs60375j).

Exciting real-world applications of photoactive nanoscale systems can indeed result from their utilization in a biomedical context. Monti and Manet (DOI: 10.1039/c3cs60402k), and Jiménez, Miranda and co-workers (DOI: 10.1039/c3cs60413f) describe how the interaction of photoactive organic compounds with either proteins or nucleic acids can be used to affect the reactivity of the resulting supramolecular assemblies for the purpose of controlling drug behaviour under light irradiation. As highlighted in the contribution of Mauro, De Cola and co-workers (DOI: 10.1039/c3cs60453e), the self-aggregation of carefully designed platinum complexes in biological environments to yield highly luminescent assemblies opens innovative routes for bioimaging. The encapsulation of appropriate photoactive molecular species within organic or inorganic nanoparticles is another powerful strategy for obtaining multifunctional and photoresponsive nanoobjects for a diversity of biomedical applications. Sortino, Raymo and co-workers (DOI: 10.1039/c3cs60324e) show that biocompatible amphiphilic polymer nanoparticles loaded with photosensitive guests have the potential of performing diagnosis and therapy in tandem, while Prodi and co-workers (DOI: 10.1039/c3cs60433k) deal with the synthesis, properties and nanomedicine applications of dye-doped luminescent silica nanoparticles.

I would like to express my gratitude to the colleagues and friends who contributed their excellent reviews. I am sure that you will enjoy reading these articles as much as I did when collecting and assembling them in the issue.

Last but not least, this issue will be an important occasion to remember Professor Nick Turro, who sadly passed away on 24 November 2012, and celebrate his enormous contribution to photochemical sciences. Entire generations of students – including myself, and certainly many contributors to this issue – started their journey in the photochemistry world through the pages of his famous book “Modern molecular photochemistry”. Nick Turro graduated from the group of Professor George Hammond, and rapidly established himself as an authority in the field of organic photochemistry and spectroscopy. In the 1980s Professor Turro began to investigate the photochemical behaviour of organic molecules included in a variety of hosts (micelles and porous inorganic solids), incorporated in dendrimers, and interacting with DNA. Indeed, he had an important role in the development of supramolecular spectroscopy and photochemistry, and continued to be at the frontline of this research field until his last days. It is not accidental, therefore, that several articles in this issue are authored by Turro's former students or collaborators. A touching editorial written by V. Ramamurthy (DOI: 10.1039/b819338j) for a themed issue of Photochem. Photobiol. Sci. dedicated to Professor Turro on his 70th birthday contains more information on him as a scientist and as a man.

A few years ago Nick Turro kindly accepted to write a brief foreword for the third edition of the CRC Handbook of Photochemistry, that I was putting together with some of my colleagues from Bologna. I was particularly struck by the final word of this short piece, which was deliberately kept isolated from the rest of the text. That word represents much of Turro's personality and his relationship with science. I would like to close this editorial in the same way.

 

Enjoy.

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