Biological oxygen measurements by phosphorescence quenching make use of exogenous phosphorescent probes, which are introduced directly into the medium of interest (e.g. blood or interstitial fluid) ...where they serve as molecular sensors for oxygen. The byproduct of the quenching reaction is singlet oxygen, a highly reactive species capable of damaging biological tissue. Consequently, potential probe phototoxicity is a concern for biological applications. Herein, we compared the ability of polyethyleneglycol (PEG)-coated Pd tetrabenzoporphyrin (PdTBP)-based dendritic nanoprobes of three successive generations to sensitize singlet oxygen. It was found that the size of the dendrimer has practically no effect on the singlet oxygen sensitization efficiency in spite of the strong attenuation of the triplet quenching rate with an increase in the dendrimer generation. This unexpected result is due to the fact that the lifetime of the PdTBP triplet state in the absence of oxygen increases with dendritic generation, thus compensating for the concomitant decrease in the rate of quenching. Nevertheless, in spite of their ability to sensitize singlet oxygen, the phosphorescent probes were found to be non-phototoxic when compared with the commonly used photodynamic drug Photofrin in a standard cell-survival assay. The lack of phototoxicity is presumably due to the inability of PEGylated probes to associate with cell surfaces and/or penetrate cellular membranes. In contrast, conventional photosensitizers bind to cell components and act by generating singlet oxygen inside or in the immediate vicinity of cellular organelles. Therefore, PEGylated dendritic probes are safe to use for tissue oxygen measurements as long as the light doses are less than or equal to those commonly employed in photodynamic therapy.
Enzyme catalysis is a powerful tool in chemical transformations, with the potential to aid the transition from fossil fuels to alternative energy carries. However, the application of enzymes is ...hindered by reduced cofactors’ high cost. This work focuses on efficient cofactor regeneration, exploring a photochemical approach inspired by natural photosynthesis. Utilizing mixed valence Bi13S18Br2 nanocrystals as photoactive catalysts, triethanolamine (TEOA) was photo-oxidized to glycolaldehyde, crucial for β-nicotinamide adenine dinucleotide (NAD+) reduction. Batch and microfluidic systems were employed, emphasizing the role of molecular oxygen in TEOA light-driven and auto-oxidation mechanisms. Indeed, the introduction of oxygen microbubbles in the microfluidic system significantly enhanced TEOA autocatalytic oxidative mechanism leading to a fivefold increase in NADH production compared to batch methods. To streamline the process and minimize operator intervention, a fully automated microfluidic system was designed, demonstrating excellent stability and reproducibility. This work provides a practical, automated, and scalable platform for real-world applications.
Exploring new materials to manipulate luminescent radiation and investigate the interaction of light and matter is one of the most compelling prospects of our century. Supramolecular chemistry has ...unraveled the opportunity to synergistically combine the chemical and optoelectronic properties of the most diverse classes of compounds. Among these, terpyridines have acted as pivotal ligand units that enable self‐assembly of multicomponent chromophoric systems. In this review we therefore elucidate the metal‐coordinating ability of these materials, that promote a plethora of aggregation‐induced phenomena. In particular, fluorescence tuning, reversible stimuli‐responsive phosphorescence enhancement and low‐dimensional complexation have been demonstrated for carbon and sulfur based terpyridine oligomeric structures. Common thread of such processes is the versatile application of light as a trigger for spectroscopic investigation and output for superior optical, medical and sensing devices.
Terpyridine is one of the most intriguing building blocks in the construction of photoactive supramolecular architectures, and light is the perfect tool to investigate their structure and to exploit optical and electronic functions.
A Barbier-type Cp2TiCl2-mediated (10 mol %) photoredox allylation of aldehydes under irradiation with visible light (blue light-emitting diodes (LEDs), 450 nm) and in the presence of an organic dye ...(3DPAFIPN, 5 mol %) with allylbromides is described.
Solar‐to‐chemical (STC) energy conversion is the fundamental process that nurtures Earth's ecosystem, fixing the inexhaustible solar resource into chemical bonds. Photochemical synthesis endows ...plants with the primary substances for their development; likewise, an artificial mimic of natural systems has long sought to support human civilization in a sustainable way. Intensive efforts have demonstrated light‐triggered production of different solar fuels, such as H2, CO, CH4 and NH3, while research on oxidative half‐reactions has built up from O2 generation to organic synthesis, waste degradation and photo‐reforming. Nevertheless, while extensive utilization of the radiant chemical potential to promote a manifold of endergonic processes is the common thread of such research, exploration of the chemical space is fragmented by the lack of a common language across different scientific disciplines. Focusing on colloidal semiconductor materials, this Viewpoint discusses an inclusive protocol for the discovery and assessment of STC redox reactions, aiming to establish photon‐to‐molecule conversion as the ultimate paradigm beyond fossil energy exploitation.
A stellar protocol: Solar‐to‐Chemical energy conversion allows the synthesis of a manifold of redox products via decoupled endergonic processes. Focusing on colloidal semiconductor materials, this Viewpoint aims to establish an interdisciplinary experimental protocol, stimulating collaborative research in photon‐to‐molecule energy conversion.
Because of a unique combination of chemical stability, redox properties, excited-state reactivity, and excited-state lifetime, Ru(bpy)
3
2+ (bpy
=
2,2′-bipyridine) and related complexes have long ...been used to obtain photoinduced intermolecular energy and electron-transfer processes. More recently these compounds have been employed as components to build up supramolecular species that exhibit peculiar photochemical and/or electrochemical properties. When suitably designed, such supramolecular species can behave as light-powered nanoscale electronic devices (e.g. wires, switches, antennas) or mechanical machines (e.g. shuttles). This paper reviews the results obtained in our research group on supramolecular species, devices and machines that exploit the properties of Ru(II) bipyridine complexes.
The pinacol coupling reaction, a reductive coupling of carbonyl compounds that proceeds through the formation of ketyl radicals in the presence of an electron donor, affords the corresponding ...1,2-diols in one single step. The photoredox version of this transformation has been accomplished using different organic dyes or photoactive metal complexes in the presence of sacrificial donors such as tertiary amines or Hantzsch's ester. Normally, the homo-coupling of such reactive ketyl radicals is neither diastereo- nor enantio-selective. Herein, we report a highly diastereoselective pinacol coupling reaction of aromatic aldehydes promoted by 5 mol% of the non-toxic, inexpensive and available Cp
2
TiCl
2
complex. The key feature that allows the complete control of diastereoselectivity is the employment of a red-absorbing organic dye in the presence of a redox-active titanium complex. Taking advantage of the well-tailored photoredox potential of this organic dye, the selective reduction of Ti(
iv
) to Ti(
iii
) is achieved. These conditions enable the formation of the
d
,
l
(
syn
) diastereoisomer as the favored product of the pinacol coupling (d.r. > 20 : 1 in most of the cases). Moreover, employing a simply prepared chiral SalenTi complex, the new photoredox reaction gave a complete diastereoselection for the
d
,
l
diastereoisomer, and high enantiocontrol (up to 92% of enantiomeric excess).
A metallaphotoredox, diastereoselective and enantioselective pinacol coupling reaction promoted by titanium complexes with the use of a red-absorbing organic dye was developed.
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 Ti
IV/III
complexes. In this minireview, we will illustrate the underlying principles and practicability of these – still uncommon – metallaphotoredox catalytic reactions.
Photochemistry and photocatalysis Balzani, Vincenzo; Bergamini, Giacomo; Ceroni, Paola
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
07/2017, Volume:
28, Issue:
Suppl 1
Journal Article
Peer reviewed
Photocatalysis is an important branch of catalysis and much more than that. To understand the potential applications and the working mechanisms of photocatalysis, it is necessary to know some ...important concepts of photochemistry, the branch of science that deals with the interaction of light and matter: (1) light excitation with a photon of suitable energy promotes a molecule or a semiconductor from the ground state to an electronically excited state that exhibits its own chemical and physical properties; (2) the most relevant consequence from the viewpoint of photocatalysis is that the excited state is both a better oxidant and a better reductant than the ground state; (3) some molecules or semiconductors can serve as photosensitizers, i.e., they can absorb light and then make available the excited state energy to promote reactions of non-absorbing species. Photosensitization and photocatalysis play an important role in nature and technology and they may take place in homogeneous or heterogeneous phase. Such processes can use sunlight (1) to convert solar energy into chemical or electrical energy, (2) to perform organic synthesis that cannot be achieved by thermal activation, and (3) to remedy pollution. Water splitting using sunlight and suitable photosensitizers and catalysts (artificial photosynthesis) is perhaps one of the most thoroughly investigated chemical processes. Breakthrough in this area can contribute to solve the energy and climate crisis, but substantial technological development is still needed.
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