Sensitized Photodecomposition of Organic Bisphosphonates By Singlet Oxygen

Phosphorus corrole complexes: from property tuning to applications in photocatalysis and triplet-triplet annihilation upconversion

Efficient triplet photosensitizers are important for fundamental photochemical studies and applications such as triplet-triplet annihilation upconversion (TTA UC), photoredox catalytic organic reactions and photovoltaics. We now report a series of phosphorus corrole compounds as efficient visible light-harvesting metal-free triplet photosensitizers. While the heavy-atom-free phosphorus corroles show absorption in the visible spectral region (centered at 573 nm) and have a decent triplet state quantum yield (Φ _Δ = 49%), iodo-substitution on the corrole core induces red-shifted absorption (589 nm) and improves intersystem crossing significantly (Φ _Δ = 67%). Nanosecond transient absorption spectra confirm triplet state formation upon photoexcitation (τ _T = 312 μs) and the iodinated derivatives also display near IR phosphorescence in fluid solution at room temperature (λ _em = 796 nm, τ _p = 412 μs). Both singlet oxygen (¹O₂) and superoxide radical anions (O₂ ^-˙) may be produced with the phosphorus corroles, which are competent photocatalysts for the oxidative coupling of benzylamine (the Aza Henry reaction). Very efficient TTA UC was observed with the phosphorus corroles as triplet photosensitizers and perylene as the triplet acceptor, with upconversion quantum yields of up to Φ _UC = 38.9% (a factor of 2 was used in the equation) and a very large anti-Stokes effect of 0.5 eV.

Excitation-Dependent Theranostic Nanosheet for Cancer Treatment

In this work, a novel ruthenium complex loaded monolayer layered double hydroxide (LDH) (denoted as Ru(C-bpy)₂ /mLDH) as supramolecular nanosensor is synthesized, which is greatly exclusive to the hypoxic tumor microenvironment. The Ru(C-bpy)₂ /mLDH ultrathin sheet displays not only enhanced luminescence lifetime compared to the parent Ru(C-bpy)₂ alone, but also improved oxygen responsibility under an excitation of 488 or 800 nm. Moreover, the Ru(C-bpy)₂ /mLDH is possessed of two-photon fluorescence imaging ability under the 800 nm irradiation. In addition, the Ru(C-bpy)₂ /mLDH can generate singlet oxygen with a high yield (φ_∆ ) of 0.28 under the 520 nm irradiation, while the φ_∆ of Ru(C-bpy)₂ is 0.19. Therefore, the Ru(C-bpy)₂ /mLDH can be applied as a supramolecular theranostic agent with light-switchable cancer imaging and photodynamic therapy properties.

Electrochemical Instability of Phosphonate-Derivatized, Ruthenium(III) Polypyridyl Complexes on Metal Oxide Surfaces

The oxidative stability of the molecular components of dye-sensitized photoelectrosynthesis cells for solar water splitting remains to be explored systematically. We report here the results of an electrochemical study on the oxidative stability of ruthenium(II) polypyridyl complexes surface-bound to fluorine-doped tin oxide electrodes in acidic solutions and, to a lesser extent, as a function of pH and solvent with electrochemical monitoring. Desorption occurs for the Ru(II) forms of the surface-bound complexes with oxidation to Ru(III) enhancing both desorption and decomposition. Based on the results of long-term potential hold experiments with cyclic voltammetry monitoring, electrochemical oxidation to Ru(III) results in slow decomposition of the complex by 2,2'-bipyridine ligand loss and aquation and/or anation. A similar pattern of ligand loss was also observed for a known chromophore-catalyst assembly for both electrochemical water oxidation and photoelectrochemical water splitting. Our results are significant in identifying the importance of enhancing chromophore stability, or at least transient stability, in oxidized forms in order to achieve stable performance in aqueous environments in photoelectrochemical devices.

Oxygen isotope signature of UV degradation of glyphosate and phosphonoacetate: tracing sources and cycling of phosphonates

The degradation of phosphonates in the natural environment constitutes a major route by which orthophosphate (Pi) is regenerated from organic phosphorus and recently implicated in marine methane production, with ramifications to environmental pollution issues and global climate change concerns. This work explores the application of stable oxygen isotope analysis in elucidating the CP bond cleavage mechanism(s) of phosphonates by UV photo-oxidation and for tracing their sources in the environment. The two model phosphonates used, glyphosate and phosphonoacetic acid were effectively degraded after exposure to UV irradiation. The isotope results indicate the involvement of both ambient water and atmospheric oxygen in the CP bond cleavage and generally consistent with previously posited mechanisms of UV-photon excitation reactions. A model developed to calculate the oxygen isotopic composition of the original phosphonate P-moiety, shows both synthetic phosphonates having distinctly lower values compared to naturally derived organophosphorus compounds. Such mechanistic models, based on O-isotope probing, are useful for tracing the sources and reactions of phosphonates in the environment.

Photoinduced electron transfer in a chromophore-catalyst assembly anchored to TiO2

Photoinduced formation, separation, and buildup of multiple redox equivalents are an integral part of cycles for producing solar fuels in dye-sensitized photoelectrosynthesis cells (DSPECs). Excitation wavelength-dependent electron injection, intra-assembly electron transfer, and pH-dependent back electron transfer on TiO(2) were investigated for the molecular assembly [((PO(3)H(2)-CH(2))-bpy)(2)Ru(a)(bpy-NH-CO-trpy)Ru(b)(bpy)(OH(2))](4+) ([TiO(2)-Ru(a)(II)-Ru(b)(II)-OH(2)](4+); ((PO(3)H(2)-CH(2))(2)-bpy = ([2,2'-bipyridine]-4,4'-diylbis(methylene))diphosphonic acid); bpy-ph-NH-CO-trpy = 4-([2,2':6',2″-terpyridin]-4'-yl)-N-((4'-methyl-[2,2'-bipyridin]-4-yl)methyl) benzamide); bpy = 2,2'-bipyridine). This assembly combines a light-harvesting chromophore and a water oxidation catalyst linked by a synthetically flexible saturated bridge designed to enable long-lived charge-separated states. Following excitation of the chromophore, rapid electron injection into TiO(2) and intra-assembly electron transfer occur on the subnanosecond time scale followed by microsecond-millisecond back electron transfer from the semiconductor to the oxidized catalyst, [TiO(2)(e(-))-Ru(a)(II)-Ru(b)(III)-OH(2)](4+)→[TiO(2)-Ru(a)(II)-Ru(b)(II)-OH(2)](4+).