Search

This work reports an examination of singlet oxygen reactions with amino acid substrates by a method involving measurement of the change in phosphorescence intensity of the singlet oxygen sensitizer. The sensitizer, a Ru(II) bipyridyl complex covalently linked to pyrene, has long-lived phosphorescence in N2 purged aqueous solutions (τ0 ~ 20 μs) that is nearly completely quenched by oxygen in aerated solutions. Irradiation of the complex in water containing sub mM concentrations of histidine, tryptophan and methionine results in a dramatic, easily visible increase in the phosphorescence intensity over a period of 10-100 s. Rate constants for singlet oxygen oxidation of each of the substrates can be obtained by using changes in the phosphorescence intensity in initial rate kinetic analysis. Rate constants obtained in this way compare favorably with those reported in the literature. The method represents a very simple approach for obtaining rate constants for singlet oxygen reactions with various substrates and the kinetics can be extended to nonaqueous solvents. [ABSTRACT FROM AUTHOR]

Excited states in transition-metalcomplexes, even in those featuringligands with strong electron donating and accepting properties, ofteninvolve only partial charge transfer between the donor and acceptorligands. The excited-state properties of [Re(bpy)(CO)3L]+compounds were studied, where L is 4-dimethylaminobenzonitrile(Re4DMABN), 3-dimethylaminobenzonitrile (Re3DMABN), and benzonitrile (ReBN) using time-resolved infrared(TRIR) and electronic spectroscopy methods as well as electronic structurecomputations. The DMABN complexes exhibit strongly solvent-dependentluminescence; the excited state lifetime decreases from microsecondsin dichloromethane to several nanoseconds in mixed MeOH:DCM (1:1)solvent. Despite the similarities in the solvent dependence of theexcited state dynamics and redox properties for Re3DMABNand Re4DMABN, the nature of the lowest energy excitedstates formed in these two compounds is drastically different. Forexample, the lowest energy excited state for Re4DMABNin the mixed solvent is assigned to the (4DMABN → bpy) ligand-to-ligandcharge transfer (LLCT) state featuring partial charge transfer character.An equilibrium between a 3DMABN intraligand triplet (3IL)and a metal-ligand-to-ligand charge transfer (MLLCT) state is foundfor Re3DMABNin the mixed solvent with the latter atca. 400 cm–1lower energy. The origin of such adrastic difference between the states involved in Re4DMABNand Re3DMABNis attributed to a difference in the energiesof polarized quinoidalresonance structures in 4DMABN and 3DMABN ligands. [ABSTRACT FROM AUTHOR]

The use of visible light to drive polymerizations with spatiotemporal control offers a mild alternative to contemporary UV-light-based production of soft materials. In this spectral region, photoredox catalysis represents the most efficient polymerization method, yet it relies on the use of heavy-atoms, such as precious metals or toxic halogens. Herein, spin-orbit charge transfer intersystem crossing from boron dipyrromethene (BODIPY) dyads bearing twisted aromatic groups is shown to enable efficient visible light polymerizations in the absence of heavy-atoms. A ≈5-15× increase in polymerization rate and improved photostability was achieved for twisted BODIPYs relative to controls. Furthermore, monomer polarity had a distinct effect on polymerization rate, which was attributed to charge transfer stabilization based on ultrafast transient absorption and phosphorescence spectroscopies. Finally, rapid and high-resolution 3D printing with a green LED was demonstrated using the present photosystem., (© 2023 Wiley-VCH GmbH.)

Halide perovskites doped with magnetic impurities (such as the transition metals Mn 2+ , Co 2+ , Ni 2+ ) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs 2 PbI 2 Cl 2 , we show that doping Mn 2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn 2+ does not replace the Pb 2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn 2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn 2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl - and two I - atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.