Porphyrin/Platinum(II) C^N^N Acetylide Complexes: Synthesis,Photophysical Properties,and Singlet Oxygen Generation

A new class of substituted porphyrins has been developed in which a different number of cyclometalated Pt^II C^N^N acetylides and polyethylene glycol (PEG) chains are attached to the meso positions of the porphyrin core, which are meant for photophysical, electrochemical, and in vitro light‐induced singlet oxygen (¹O₂) generation studies. All of these Zn^II porphyrin–Pt^II C^N^N acetylide conjugates show moderate to high (Φ_Δ=0.55 to 0.63) singlet oxygen generation efficiency. The complexes are soluble in organic solvents but, despite the PEG substituents, slowly aggregate in aqueous solvent systems. These conjugates also exhibit interesting photophysical properties, including near‐complete photoinduced energy transfer (PEnT) through the rigid acetylenic bond(s) from the Pt^II C^N^N antenna units to the Zn^II porphyrin core, which shows sensitized luminescence, as shown by quenching of Pt^II C^N^N‐based luminescence. Electrochemical measurements show a set of redox processes that are approximately the sum of what is observed for the Pt^II C^N^N acetylide and Zn^II porphyrin units. UV/Vis spectroscopic properties are supported by DFT calculations.     

Exotic electron states and tunable magneto-transport in a fractal Aharonov–Bohm interferometer

A Sierpinski gasket fractal network model is studied in respect of its electronic spectrum and magneto-transport when each ‘arm’ of the gasket is replaced by a diamond shaped Aharonov–Bohm interferometer, threaded by a uniform magnetic flux. Within the framework of a tight binding model for non-interacting, spinless electrons and a real space renormalization group method we unravel a class of extended and localized electronic states. In particular, we demonstrate the existence of extreme localization of electronic states at a special finite set of energy eigenvalues, and an infinite set of energy eigenvalues where the localization gets ‘delayed’ in space (staggered localization). These eigenstates exhibit a multitude of localization areas. The two terminal transmission coefficient and its dependence on the magnetic flux threading each basic Aharonov–Bohm interferometer is studied in details. Sharp switch on–switch off effects that can be tuned by controlling the flux from outside, are discussed. Our results are analytically exact.     

Benzimidazolium-based new simple ratiometric fluorescent sensor for selective detection of dihydrogenphosphate

A series of pyridine-coupled benzimidazolium-based receptors 1, 2 and 3 have been designed and synthesised. In the series, only receptor 1 is structurally appealing in the selective recognition of H₂PO₄^?  in CHCl₃ as well as in CH₃CN over a series of other anions. The ratiometric change in emission with a triplet band at 420 nm is the distinctive feature of selective recognition of H₂PO₄^?  in CHCl₃. In CH₃CN, a ‘turn on’ response is selectively observed. Binding studies have been carried out using fluorescence, UV–vis, ¹H NMR and ³¹P NMR spectroscopic techniques. Experimental results have been correlated with the theoretical findings.     

Biomimetic multifunctional porous chalcogels as solar fuel catalysts

Biological systems that can capture and store solar energy are rich in a variety of chemical functionalities, incorporating light-harvesting components, electron-transfer cofactors, and redox-active catalysts into one supramolecule. Any artificial mimic of such systems designed for solar fuels production will require the integration of complex subunits into a larger architecture. We present porous chalcogenide frameworks that can contain both immobilized redox-active Fe(4)S(4) clusters and light-harvesting photoredox dye molecules in close proximity. These multifunctional gels are shown to electrocatalytically reduce protons and carbon disulfide. In addition, incorporation of a photoredox agent into the chalcogels is shown to photochemically produce hydrogen. The gels have a high degree of synthetic flexibility, which should allow for a wide range of light-driven processes relevant to the production of solar fuels.     

Site-selective detection of vibrational modes of an iron atom in a trinuclear complex

Nuclear inelastic scattering (NIS) experiments on the trinuclear complex [⁵⁷Fe{L-N₄(CH₂Fc)₂} (CH₃CN)₂](ClO₄)₂ have been performed. The octahedral iron ion in the complex was labelled with ⁵⁷Fe and thereby exclusively the vibrational modes of this iron ion have been detected with NIS. The analysis of nuclear forward scattering (NFS) data yields a ferrous low-spin state for the ⁵⁷Fe labelled iron ion. The simulation of the partial density of states (pDOS) for the octahedral low-spin iron(II) ion of the complex by density functional theory (DFT) calculations is in excellent agreement with the experimental pDOS of the complex determined from the NIS data obtained at 80 K. Thereby it was possible to assign almost each of the experimentally observed NIS bands to the corresponding molecular vibrational modes.     

Isostructural Nanocluster Manipulation Reveals Pivotal Role of One Surface Atom in Click Chemistry

Elucidating single-atom effects on the fundamental properties of nanoparticles is challenging because single-atom modifications are typically accompanied by appreciable changes to the overall particle's structure. Herein, we report the synthesis of a [Cu₅₈H₂₀PET₃₆(PPh₃)₄]²⁺ ( Cu₅₈ ; PET: phenylethanethiolate; PPh₃: triphenylphosphine) nanocluster—an atomically precise nanoparticle—that can be transformed into the surface-defective analog [Cu₅₇H₂₀PET₃₆(PPh₃)₄]⁺ ( Cu₅₇ ). Both nanoclusters are virtually identical, with five concentric metal shells, save for one missing surface copper atom in Cu₅₇ . Remarkably, the loss of this single surface atom drastically alters the reactivity of the nanocluster. In contrast to Cu₅₈ , Cu₅₇ shows promising activity for click chemistry, particularly photoinduced [3+2] azide-alkyne cycloaddition (AAC), which is attributed to the active catalytic site in Cu₅₇ after the removal of one surface copper atom. Our study not only presents a unique system for uncovering the effect of a single-surface atom modification on nanoparticle properties but also showcases single-atom surface modification as a powerful means for designing nanoparticle catalysts.