Three azobenzene-core-based molecular systems decorated with rhodamine units were designed and developed as photoswitchable multianalyte sensors. The systems were employed in the detection of multiple metal ions (Fe(III), Fe(II), Sn(II) and Al(III)).

Abstract

We have developed three azobenzene-core-based molecular systems decorated with different numbers of rhodamine units as photoswitchable multianalyte sensors. Exploiting the ring-opening of the spirolactam part of the rhodamine unit, the resulting fluorescence response, and modulation of it through the photoswitching of azobenzene by light, we utilized them in the detection of multiple metal ions (Fe³⁺, Fe²⁺, Sn²⁺ and Al³⁺). The binding sites, stoichiometry, binding constants, fluorescent lifetimes and limit of detection (LOD) for each probe have been deduced using appropriate spectroscopic techniques. The limit of detection (LOD) of 5 a, 5 b and 5 c for Fe³⁺ are found to be 4.2×10⁻⁷±7.8×10⁻⁹ M, 2.2×10⁻⁷±4.6×10⁻⁹ M and 1.2×10⁻⁷±4.6×10⁻⁹ M, respectively. The fluorescence response of the metal-chelated complex can be manipulated effectively by employing the photoswitching ability of azobenzene that makes them useful as chemosensors for various individual metal ions.

Herein we report on a non-approximative analysis of delayed fluorescence and study the triplet-triplet annihilation process of the PtOEP/9,10-DPA and PdOEP/9,10-DPA sensitizer/acceptor pairs in different solvents (THF, DMSO and toluene).

Abstract

The molecular processes taking place during triplet-triplet annihilation (TTA) in solvents at room temperature are examined in detail. Special attention is paid to modelling of the nonlinear kinetic reactions. Using time- and spectrally resolved spectroscopy of DPA and Pt/Pd-OEP based sensitizer and annihilators, it is shown how the kinetic of parameters, such as the triplet energy transfer (TET) and TTA of the rate-reactions, can be simulated, measured and fitted, without approximations, using a numerical scheme. Studies of DPA in the solvents DMSO, THF and toluene at room temperature revealed that viscosity/diffusion together with the excited triplet lifetime of the annihilator are the most crucial parameters for high TTA induced delayed fluorescence. From an analysis of the experimentally determined rates an efficiency of 16–40 % was determined for the combined TET and TTA processes using THF, DMSO and toluene as solvents. (DPA=9,10-diphenylanthracene, OEP=2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin)

Water-soluble dyes based on perylene diimide molecules were employed as molecular catalysts for the light-induced conversion of dissolved oxygen to hydrogen peroxide. Improved photocatalytic efficiency was achieved by using quaternary ammonium solubilizing units on the perylene diimide core and with selection of sacrificial electron donors.

Abstract

Photocatalytic generation of hydrogen peroxide, H₂O₂, has gained increasing attention in recent years, with applications ranging from solar energy conversion to biophysical research. While semiconducting solid-state materials are normally regarded as the workhorse for photogeneration of H₂O₂, an intriguing alternative for on-demand H₂O₂ is the use of photocatalytic organic dyes. Herein we report the use of water-soluble dyes based on perylene diimide molecules which behave as true molecular catalysts for the light-induced conversion of dissolved oxygen to hydrogen peroxide. In particular, we address how to obtain visible-light photocatalysts which are stable with respect to aggregation and photochemical degradation. We report on the factors affecting efficiency and stability, including variable electron donors, oxygen partial pressure, pH, and molecular catalyst structure. The result is a perylene diimide derivative with unprecedented peroxide evolution performance using a broad range of organic donor molecules and operating in a wide pH range.

Steady state and time-resolved spectroscopy reveal the enhanced solvatochromism, aggregation induced enhanced emission and protonation controlled dual emission of a dimethyladrydan pyrimidine chromophore.

Abstract

A pyrimidine chromophore bearing an acridan fragment was synthesized and its photophysical properties were studied. In solution, this compound is characterized by an important positive emission solvatochromism with a shift of 5800 cm⁻¹ between nonpolar heptane and dichloromethane (DCM) associated with large Stokes shifts (up to 9100 cm⁻¹ in DCM). Mono-exponential fluorescence decays are observed in heptane whereas more complicated bi- or three-exponential decays are observed in more polar solvents due to an interplay between locally excited and charge transfer excited state. Additionally, an aggregation-induced enhanced emission process was demonstrated in THF/water mixtures. At low temperature (77 K), in a polymethylmethacrylate (PMMA) thin film, the presence of an accessible triplet state (T1) was demonstrated, which was not observed in solution. Finally, we show that it is possible to protonate the chromophore in thin film leading to panchromatic dual emission

Azoheteroarenes are an emerging class of photoswitch that offer distinct features such as efficient photoisomerization, variable stability of the photoswitched states, and bidirectional photoswitching. This Review overviews different classes of azoheteroarene-coordinated metal complexes reported in the literature. It also surveys their achievements in optical, magnetic properties, metallo-supramolecular chemistry, and catalysis, as well as the use of light to control them. (Image adapted from: Inorg. Chem. Front. 2022, 9, 2315–2327).

Abstract

Azoheteroarenes are emerging classes of photoswitches with versatile scaffolds that offer distinct features such as efficient photoisomerization, tunable stability of the photoswitched states, and bidirectional photoswitching. Moreover, the heteroatoms of such photoswitches exhibit coordination ability to bind to the metal centers. The resulting azoheteroarene-based metal complexes can be designed and developed to tune various metal-based properties towards intriguing applications such as in optics, magnetic properties, data storage applications, and catalysis. Despite the diverse utility of azopyridines in such contexts, other azoheteroarenes, particularly the state-of-the-art five-membered heterocycle-based photoswitches, remain under-explored. In this Review, we describe the diverse classes of azoheteroarene-coordinated metal complexes reported in the literature and survey their photoswitching behaviour and applications. Furthermore, we identify potential azoheteroarene candidates for building photochrome-coupled metal complexes and supramolecular architectures for maximizing the photo-tuning of metal-related properties.

A photo-induced transformation, specific to the nanometric size and different from the well-documented photo-induced electron transfer in molecules and large size coordination polymers, is evidenced in 5 nm nanocrystals of an alkali cation free CoFe Prussian blue analog by SQUID magnetometry and X-ray absorption spectroscopy.

Abstract

The discovery of a photomagnetic effect in a CoFe Prussian blue analog (PBA) has triggered a growing interest for photo-switchable bimetallic cyanide-bridged systems. Nevertheless, in between cyanide-bridged extended coordination polymers and discrete molecules, the photo-switching phenomena are much less well known in nano-sized materials. A photo-induced transformation, specific to the nanometric size, is evidenced by magnetometry and by X-ray absorption spectroscopy at the Co and Fe K-edges in an alkali cation free Prussian blue analog. The nanoparticles before irradiation can be described as having a core-shell structure, the core being made of the well-known fcc-Co^II(HS)Fe^III structure of CoFe PBAs while the shell contains Co^II ions in octahedral geometry and significantly distorted Fe(CN)₆ entities. Irradiation induces a change of the local structures around the transition metal ions, which remain in the same oxidation state, with different behaviors of the Co and Fe sub-lattices.

The Front Cover shows various luminescent nano-assemblies flying into cells and lighting them for cell imaging. Non-covalent interaction and binding enable the formation of dynamic supramolecular self-assemblies, realizing in situ control of luminescence and loading capacity for diagnosis, drug delivery, and treatment. More information can be found in the Review Article by Xu-Man Chen, Quan Li and co-workers.

Let's see… Recent advances in the development and application of supramolecular luminescent nano-assemblies based on different functional building blocks in cell imaging are reviewed. These supramolecular luminescent nano-assemblies have wide applications in targeted imaging of specific organelles, drug delivery, and therapy.

Abstract

Supramolecular luminescent nano-assemblies for cell imaging have recently attracted increasing interest, not only because of their outstanding photophysical properties, but also because of their easy fabrication through supramolecular strategies, good biocompatibility, high stability to photo- and micro-environments in cells, and facile combination of imaging and synergistic therapy for cancers. Luminescence-based bioimaging has great advantages, such as high sensitivity, being non-invasive, and functioning in real-time, leading to its wide application in many fields, including disease research, drug research, cell markers, gene expression, gene function studies, and protein interaction. In this Review, recent progress in the application of macrocycle-mediated (e.g., cyclodextrins, cucurbiturils, calixarenes, and pillar[n]arenes) and functionalized amphiphilic molecule-based supramolecular luminescent nanoparticles in cell imaging, especially targeted cell imaging of specific organelles, is reviewed. The combination of imaging with drug delivery, gene delivery, and photodynamic therapy is also introduced.