An all-atom 5 nanosecond molecular dynamics simulation of a water-solvated micelle containing 60 sodium dodecyl sulfate monomers was performed. Structural properties such as the radius of gyration, eccentricity, micellar size, accessible surface area, dihedral angle distribution, carbon atom distribution, and the orientation of the monomers toward the micelle center of mass were evaluated. The results indicate a stable micellar system over the duration of the simulation. Evaluation of the structure and motion of the sodium counterions show (1) a long equilibration time (1 nanosecond) is required to achieve a stable distribution of counterions and (2) approximately 25% of the sodium ions are located in the first shell and 50% are located in the first two shells of the micelle during the course of the simulation. The structure of the micelle oxygen-sodium ion radial distribution function reveals two distinct peaks which divide the counterions into those close to the micelle (first shell) those far from the micelle (bulk) and those between (second shell). Finally, values of the diffusion coefficient for sodium ions followed a decreasing trend for ions in the bulk of the micellar system (D ) 1.9 × 10 -5 cm 2 /s), ions in the second shell of the micelle (D ) 1.4 × 10 -5 cm 2 /s), and those in the first shell of the micelle (D ) 1.0 × 10 -5 cm 2 /s).

The emitting metal-to-ligand charge transfer (MLCT) excited state of [Ru(bpy)2(bpz)]2+ (bpy is 2,2‘-bipyridine; bpz is 2,2‘-bipyrazine) is reductively quenched by hydroquinone (H2Q) by proton-coupled electron transfer (PCET), most likely by concerted electron−proton transfer (EPT). The identity of the transient products ([Ru(bpy)2(bpzH•)]2+ and HQ•) and the kinetics of their formation and disappearance have been established by steady-state emission and time-resolved emission, absorption, and EPR measurements. The protonated, reduced complex [Ru(bpy)2(bpzH•)]2+ functions as a H-atom reductant toward quinone or benzaldehyde with potential implications for net photochemistry and energy conversion.

Abstract— Steady‐state and time‐resolved electron paramagnetic resonance (TREPR) experiments are described. Comparison of the TREPR continuous wave method to other time domain EPR techniques such as Fourier transform EPR (FT‐EPR) is made, and the advantages and disadvantages of each are presented. The role played by several mechanisms of chemically induced dynamic electron spin polarization (CIDEP) in the appearance of the spectra is explained. The advantages of using higher frequency spectrometers than the standard X‐band (9.5 GHz) are presented and discussed. Examples are presented that are relevant to organic photochemistry and electron donor‐acceptor chemistry. The use of TREPR to study polymer photodegradation, polymer chain dynamics, free radical initiator chemistry and biradical spin exchange interactions is described. Emphasis is placed on magnetic field effects studied by multiple frequency TREPR in these systems. Finally, several future directions in the field are discussed in terms of new developments in microwave and magnetic field technology.

Spin and conformational dynamics in symmetric alkyne-bridged multi[copper(II) porphyrin] structures have been studied in toluene solution at variable temperature using steady-state electron paramagnetic resonance (EPR) spectroscopy. Comparison of the dimer EPR spectra to those of Cu porphyrin monomers shows evidence of an isotropic exchange interaction (J) in these biradicaloid structures, manifested by a significant line broadening in the dimer spectra. The extent line broadening depends on molecular structure and temperature, suggesting J is modulated by conformational dynamics that impact the torsional angle distribution between the porphyrin-porphyrin least-squares planes. Computational simulation of the experimental EPR spectra, using a developed algorithm for J modulation in flexible organic biradicals, supports this hypothesis. Comparison of ethyne and butadiyne alkyne bridges reveals remarkable sensitivity to orbital interactions between the spacer and the metal, reflected in measurements of J as a function of temperature. The results suggest orbital symmetry relationships may be more important than recognized in design of optimized molecular spintronic devices.

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