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The article focuses on radicals with multiple personalities, based from combined theoretical and experimental approach. It mentions that distonics ions are ions that contain both positive and negative charges. It states that tetrathiofulvalene-nitronylnitroxide (TTF-NN) complex is an example of orbital energy-level conversion, in which radical centre of singly occupied molecular orbital (SOMO) has lower energy compared to doubly occupied molecular orbital (HOMO). It adds that mass spectrometrist Stephen Blanskby and computational chemist Michelle Coote has suggested that orbital conversion in distonic anion are common that usually thought.

In the second paper, spectral decomposition is used to explain the origin of the asymmetry of the anti-phase structure (APS) and its temperature dependence in dynamic spin correlated radical pairs (SCRPs) created via the photoreduction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micelles. It is shown that the main parameters defining the spectral shape of the TREPR spectra are the effectiveness of the electron spin exchange in contact pairs, and the ratio of the frequency of enforced encounters (Z) to the frequency of singlet–triplet mixing (q) in the separated radical pairs. The Z/q ratio is particularly important for the creation of the APS asymmetry. The existence of different q values in the same TREPR spectrum in this system affords the observation of SCRPs in both regimes: exchange broadening (large ☋q☋/Z) and exchange narrowing (small ☋q☋/Z). An important observation, supported by the successful simulation of the TREPR spectra, is that the S-component of the APS can be shifted in a direction opposite to that predicted by the earlier Closs–Forbes–Norris (CFN) model. This result is naturally explained in terms of a spectral exchange approach. Dispersion-like components in the spectra further amplify the asymmetry of the APS. [ABSTRACT FROM AUTHOR]

The photochemistry of Fe(III) coordinated to natural uronate-containing polysaccharides has been investigated quantitatively in aqueous solution. It is demonstrated that the photoreduction of the coordinated Fe(III) to Fe(II) and oxidative decarboxylation occurs in a variety of uronate-containing polysaccharides. The photochemistry of the Fe(III)-polyuronic acid system generated a radical species during the reaction which was studied using the spin trapping technique. The identity of the radical species from this reaction was confirmed as CO2•− indicating that both bond cleavage of the carboxylate and oxidative decarboxylation after ligand to metal charge transfer radical reactions may be taking place upon irradiation. Degradation of the polyuronic acid chain was investigated with dynamic light scattering, showing a decrease in the hydrodynamic radius of the polymer assemblies in solution after light irradiation that correlates with the Fe(II) generation. A decrease in viscosity of Fe(IIII)-alginate after light irradiation was also observed. Additionally, the photochemical reaction was investigated in plant root tissue (parsnip) demonstrating that Fe(III) coordination in these natural materials leads to photoreactivity that degrades the pectin component. These results highlight that this Fe(III)-polyuronic acid can occur in many natural systems and may play a role in biogeochemical cycling of iron and ferrous iron generation in plants with significant polyuronic acid content. [ABSTRACT FROM AUTHOR]

The photophysics and reactivity of two tetraphenylborate salts and triphenylborane have been studied using ultrafast transient absorption, steady-state fluorescence, electron paramagnetic resonance with spin trapping, and DFT calculations. The singlet excited state of tetraarylborates exhibit extended π-orbital coupling between two adjacent aryl groups. The maximum fluorescence band, as well as the transient absorption bands centered at 560 nm (τ = 1.05 ns) and 680 nm (τ = 4.35 ns) are influenced by solvent viscosity and polarity, indicative of a twisted intramolecular charge transfer (TICT) state. Orbital contour plots of the HOMO and LUMO orbitals of the tetraarylboron compounds support the existence of electron delocalization between two aryl groups in the LUMO. This TICT-state and aryl–aryl electron extension is not observed for the trigonal arylboron compound, in which excited π-orbital coupling only occurs between the boron atom and one aryl group, which restricts the twist motion of the aryl–boron bond. The excited triplet state is deactivated primarily through aryl–boron bond cleavage, yielding aryl and diphenylboryl radicals. In the presence of oxygen, this photochemistry results in phenoxyl and diphenylboroxyl radicals, as confirmed by EPR spectroscopy of spin trapped radical adducts. The TICT transition and radical generation is not expected for BoDIPY molecules where the rotational vibration of the B–aryl bond is rigid, restricting changes in the geometric structure. In this sense, this work contributes to the development of new BoDIPY derivatives where the TICT transition may be observed for aryl ligands with free rotational vibrations in the BoDIPY structure. [ABSTRACT FROM AUTHOR]

Reaction kinetics for two sterically hindered secondary amines with singlet oxygen have been studied in detail. A water soluble porphyrin sensitizer, 5,10,15,20-tetrakis-(4-sulfunatophenyl)-21,23H-porphyrin (TPPS), was irradiated in oxygenated aqueous solutions containing either 2,2,6,6-tetramethylpiperidin-4-one (TMPD) or 4-[N,N,N-trimethyl-ammonium]-2,2,6,6-tetramethylpiperidinyl chloride (N-TMPCl). The resulting sensitization reaction produced singlet oxygen in high yield, ultimately leading to the formation of the corresponding nitroxide free radicals (R2NO) which were detected using steady-state electron paramagnetic resonance (EPR) spectroscopy. Careful actinometry and EPR calibration curves, coupled with a detailed kinetic analysis, led to a simple and compact expression relating the nitroxide quantum yield ΦR2NO (from the doubly-integrated EPR signal intensity) to the initial amine concentration [R2NH]i. With all other parameters held constant, a plot of ΦR2NOvs. [R2NH]i gave a straight line with a slope proportional to the rate constant for nitroxide formation, kR2NO. This establishment of a rigorous quantitative relationship between the EPR signal and the rate constant provides a mechanism for quantifying singlet oxygen production as a function of its topology in heterogeneous media. Implications for in vivo assessment of singlet oxygen topology are briefly discussed. [ABSTRACT FROM AUTHOR]

Radical pairs created by the photoreduction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micelles exhibit strong asymmetry in the line shapes of their time-resolved electron paramagnetic resonance (TREPR) signals. The asymmetry is strongly dependent on the temperature from 16 °C to 66 °C. Simulations of the anti-phase structure (APS) line shape of these spin correlated radical pairs (SCRPs), based on a numerical solution of the Stochastic Liouville Equation with the spin exchange interaction depending exponentially on the distance between radicals, are presented and discussed. The proposed model takes into account the diffusive motion of the radicals along with the motion of the transverse magnetization and accounts satisfactorily and self-consistently for the asymmetry of the observed TREPR signals. [ABSTRACT FROM AUTHOR]