Energy up‐conversion is the process by which two absorbed photons are converted in one photon of higher energy. Such a process can be conveniently performed by low‐power excitation through sensitized ...triplet–triplet annihilation and it is now an emerging technique with possible applications in different fields, including photovoltaic devices and bioimaging.
Up, up and away: Energy up‐conversion, the generation of a high‐energy excited state by absorption of two low‐energy photons, is an emerging technique with possible applications in different fields, such as harnessing red or infrared solar photons to power photovoltaic devices.
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Phosphorescent materials are mostly based on metal complexes. Metal-free organic molecules usually display phosphorescence only in a rigid matrix at 77 K. In the last few years, there has been ...increasing interest in the design of organic molecules displaying long-lived and highly intense room-temperature phosphorescence, an extremely difficult task since these two properties are generally conflicting. This review reports the most recent and tutorial examples of molecules that are weakly or non-phosphorescent in deaerated fluid solution and whose room temperature phosphorescence is switched on upon aggregation. The examples are divided into two classes according to the mechanism responsible for switching on phosphorescence: (i) rigidification by crystallization or by encapsulation in a polymeric matrix and (ii) interaction with other molecules of the same type (self-aggregation) or a different type by taking advantage of heavy-atom effects.
This feature article presents the principles and most recent examples of organic molecules in which long lived and highly intense room-temperature phosphorescence is switched on by rigidification of the matrix in a crystal or in a polymer or by interaction with other molecules.
BODIPYs are renowned fluorescent dyes with strong and tunable absorption in the visible region, high thermal and photo-stability and exceptional fluorescence quantum yields. Transition metal ...complexes are the most commonly used triplet photosensitisers, but, recently, the use of organic dyes has emerged as a viable and more sustainable alternative. By proper design, BODIPY dyes have been turned from highly fluorescent labels into efficient triplet photosensitizers with strong absorption in the visible region (from green to orange). In this perspective, we report three design strategies: (i) halogenation of the dye skeleton, (ii) donor-acceptor dyads and (iii) BODIPY dimers. We compare pros and cons of these approaches in terms of optical and electrochemical properties and synthetic viability. The potential applications of these systems span from energy conversion to medicine and key examples are presented.
BODIPYs offer a versatile platform to build organic triplet photosensitisers for PDT, TTA upconversion and photocatalysis. Tuning their properties provides the opportunity of replacing heavy-metal complexes and can lead to improved sustainability.
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•Ruthenium tris(bipyridine) is a most influential molecule in contemporary chemistry.•Ru-polypyridine complexes exhibit a unique combination of ground- and excited-state properties.•Ru-polypyridine ...complexes are convenient building blocks in supramolecular photochemistry.•Valuable functions arise from photoinduced energy/electron transfer in multicomponent systems.•Integration with mechanically interlocked molecules can lead to nanomachines.
This review deals with a very peculiar molecule, Ru(bpy)32+ (bpy: 2,2′-bipyridine), and its interaction with photons and electrons. We summarize the properties that make Ru(bpy)32+ and related compounds a unique family of “clever” molecules which find application as components of chemical species capable of processing optical and electrical signals to perform a variety of interesting functions. Examples discussed in the article, that showcase the realization of these concepts with molecular and supramolecular systems, include molecular wires, switches, antennas and mechanical machines.
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5.
Light: A Very Peculiar Reactant and Product Balzani, Vincenzo; Bergamini, Giacomo; Ceroni, Paola
Angewandte Chemie (International ed.),
September 21, 2015, Volume:
54, Issue:
39
Journal Article
Peer reviewed
Open access
See the light of day: Light is the fastest way of transferring energy and information through space, and in chemistry it can perform the dual role of reactant and product. Sunlight, a really unique ...reactant, represents our ultimate energy source. Chemists are engaged in designing systems for the conversion of light into electrical or chemical energy and vice versa to create a more sustainable way of life.
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The development of multicomponent (supramolecular) systems that can perform predetermined functions under external control -
i.e.
, molecular devices - is a challenging task in chemistry and a ...fascinating objective in the frame of a bottom-up approach to nanostructures. In this context light signals can be conveniently used both for supplying energy to the system and for probing its states and transformations. The aim of this tutorial review is to recall a few basic aspects of light-induced processes that can be used to "write" and "read" onto molecular and supramolecular systems. These principles are illustrated through some examples of artificial molecular devices and machines taken from our work, which provide a flavour of current research. They are molecular and supramolecular systems that operate and/or perform valuable functions by exploiting photoinduced energy- or electron-transfer processes, photoisomerization reactions, or photoinduced proton transfer. The choice of these examples was based on both their intrinsic importance for the referred topic and their educational value. In the last section of the review potential applications, limitations and future directions of the research in the field of artificial molecular devices and machines are also discussed.
Functional supramolecular systems can exploit photoinduced processes for gaining energy as well as for providing information on their state. We discuss the operation of these species from a fundamental viewpoint and we illustrate their potential to function as nanoscale devices and machines by means of selected examples.
Phosphorescence is generally considered a property of metal complexes; conversely, organic molecules are usually phosphorescent only at 77 K, where non-radiative decays are slowed down and quenching ...by dioxygen is inhibited. In this issue of Chem, Tang and colleagues report on rational guidelines for the design of organic chromophores exhibiting long-lived and bright phosphorescence at ambient conditions.
Phosphorescence is generally considered a property of metal complexes; conversely, organic molecules are usually phosphorescent only at 77 K, where non-radiative decays are slowed down and quenching by dioxygen is inhibited. In this issue of Chem, Tang and colleagues report on rational guidelines for the design of organic chromophores exhibiting long-lived and bright phosphorescence at ambient conditions.
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A hexathiobenzene molecule carrying six terpyridine (tpy) units at the periphery has been designed to couple the aggregation induced phosphorescence, displayed by the core in the solid state, to the ...metal binding properties of the tpy units. Upon Mg2+ complexation in THF solution, phosphorescence of the hexathiobenzene core is turned on. Metal ion coordination yields the formation of a supramolecular polymer which hinders intramolecular rotations and motions of the core chromophore, thus favoring radiative deactivation of the luminescent excited state. Upon excitation of the Mg(tpy)22+ units of the polymeric structure, sensitization of the core phosphorescence takes place with >90% efficiency. The light-harvesting polymeric antenna can be disassembled upon fluoride ion addition, thereby switching off luminescence and offering a new tool for fluoride ion sensing. This unique system can, thus, serve as cation or anion sensor.
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The photocatalytic mechanism reported in a recent Communication to produce the radical anion of pyrenes postulates a highly endergonic electron transfer process. An analysis of the thermodynamics is ...reported together with the proposal of an alternative thermodynamically feasible mechanism.
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The development of solid materials that can be reversibly interconverted by light between forms with different physico-chemical properties is of great interest for separation, catalysis, ...optoelectronics, holography, mechanical actuation and solar energy conversion. Here, we describe a series of shape-persistent azobenzene tetramers that form porous molecular crystals in their E-configuration, the porosity of which can be tuned by changing the peripheral substituents on the molecule. Efficient E→Z photoisomerization of the azobenzene units takes place in the solid state and converts the crystals into a non-porous amorphous melt phase. Crystallinity and porosity are restored upon Z→E isomerization promoted by visible light irradiation or heating. We demonstrate that the photoisomerization enables reversible on/off switching of optical properties such as birefringence as well as the capture of CO2 from the gas phase. The linear design, structural versatility and synthetic accessibility make this new family of materials potentially interesting for technological applications.
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