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.
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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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 framework of solar-to-chemical energy conversion is mapped by an exploding investigation space, aiming at rapid elevation of the technology to commercially relevant performances and processing ...conditions. Prospective materials and alternative oxidative pathways are revolutionizing water-splitting into decoupled hydrogen and high-value added chemicals production. Yet, pioneering solar refinery systems have been limited to either efficient, but isolated half-reactions or sluggish simultaneous red-ox transformations, hampering the forthcoming adoption of this promising solar-harvesting strategy. Here, we provide the first demonstration of efficient and stable full-cycle redox transformations, synthesising solar chemicals.
The identification of a successful redox cycle ensued from fluorescent quenching screening, which bridges between optoelectronic material properties and photosynthetic activity. Implementing this approach on hybrid nanorod photocatalysts (CdSe@CdS–Pt), we demonstrate hydrogen production with photon to hydrogen quantum efficiencies of up to ~70%, under visible light and mild conditions, while simultaneously harvesting solar chemical potential for valuable oxidative chemistries. Facile spectrophotometric analyses further show robust photo-chemical and colloidal stability, as well as product selectivity when converting molecules carrying amino- and alcohol-groups, with solar-to-chemical energy conversion efficiencies of up to 4.2%. As such, rigorous spectroscopic assessment and operando characterization yield superior photosynthetic performance, realizing a truly light-triggered catalytic reaction and establishing nanostructured metal-chalcogenide semiconductors as state-of-the-art artificial photo-chemical devices.
Towards Solar Factories, following Ciamician's Dream (Science, 1912): “Forests of glass tubes will extend over the plains and glass buildings will extend everywhere; inside of these will take place the photochemical processes that hitherto have been the guarded secret of the plants”. Display omitted
•Photosynthetic solar-to-chemical (STC) energy conversion entails fuels and valuable chemicals production.•4.2% STC conversion efficiency demonstrates a practical route beyond overall water splitting.•Hybrid semiconductor nanorods allow highly efficient operation in mild condition without sacrificial reagent.•Spectro-photometric screening and analyses unravel long-term chemical and colloidal stability.
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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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IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, UL, UM, UPUK
Organometallic allylic reagents are widely used in the construction of C−C bonds by Barbier‐type reactions. In this communication, we have described a photoredox Barbier allylation of aldehydes ...mediated by bismuth, in absence of other metals as co‐reductants. Mild reaction conditions, tolerance of oxygen, and use of aqueous solvent make this photoredox methodology attractive for green and sustainable synthesis of homoallylic alcohols.
Green Photoredox! Negligibly toxic bismuth salts can be employed in a photoredox allylation of aldehydes mediated by an organic dye. To further add interest to this new methodology, the photoredox Barbier allylation is carried out in EtOH/water and shows low sensitivity to oxygen and radical scavengers.
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A practical and effective photoredox propargylation of aldehydes promoted by 10 mol % of Cp2TiCl2 is presented. No stoichiometric metals or scavengers are used for the process. A catalytic amount of ...the cheap and simply prepared organic dye 3DPAFIPN is used as the reductant for titanium. The reaction displayed a broad scope, and no traces of allenyl isomers were detected for simple propargyl bromide, whereas mixtures of propargyl and allenyl isomers were observed for substituted propargyl bromides.
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Titanium is one of the most abundant and environmentally innocuous metals. Ti‐based organometallic compounds have long been used as versatile homogeneous catalysts in synthetic chemistry and still ...remain highly attractive for the development of sustainable transformations. With the emerging role of photoredox catalysis, the selectivity of the radical initiation in electron transfer‐mediated reactions has been shown to be fundamental in terms of synthesis efficiency. Recent examples have displayed the effectiveness of inorganic and organic chromophores at the excited state in triggering the redox chemistry of TiIV/III complexes. In this minireview, we will illustrate the underlying principles and practicability of these – still uncommon – metallaphotoredox catalytic reactions.
Metallaphotoredox catalysis is emerging as an excellent and versatile cornerstone for the development of modern synthetic methodologies. Recent examples have displayed how the redox chemistry of titanium‐based complexes can be triggered by organic and inorganic chromophores in catalytic processes activated by visible‐light, affording synthetically demanding products.
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Photoluminescence of silicon nanocrystals (SiNCs) in the presence of a series of quinone electron acceptors and ferrocene electron donors is quenched by oxidative and reductive electron transfer ...dynamic processes, respectively. The rate of these processes is investigated as a function of (a) the thermodynamic driving force of the reaction, by changing the reduction potentials of the acceptor or donor molecules, (b) the dimension of SiNCs (diameter = 3.2 or 5.0 nm), (c) the surface capping layer on SiNCs (dodecyl or ethylbenzene groups), and (d) the solvent polarity (toluene vs dichloromethane). The results were interpreted within the classical Marcus theory, enabling us to estimate the position of the valence and conduction bands, as well as the reorganization energy (particularly small, as expected for quantum dots) and electronic transmission coefficients. The last parameter is in the range 10–5–10–6, demonstrating the nonadiabaticity of the process, and it decreases upon increasing the SiNC dimensions: this result is in line with a larger number of excitons generated in the inner silicon core for larger SiNCs and thus resulting in a lower electronic coupling with the quencher molecules.
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