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We discuss the possibility of using circularly polarized luminescence (CPL) as a tool to probe individual triplet spin sublevels that are populated nonadiabatically following photoexcitation. This study is motivated by a mechanism proposed for chirality-induced spin selectivity in which coupled electronic-nuclear dynamics may lead to a non-statistical population of the three triplet sublevels in chiral systems. We find that low-temperature CPL should aid in quantifying the exact spin state/s populated through coupled electronic-nuclear motion in chiral molecules. [ABSTRACT FROM AUTHOR]

The article discusses the chiral induced spin selectivity effect (CISS), which is the finding that the motion of an electron within or through chiral systems depends on the spin of that electron. The article explains that while the effect has been observed experimentally, developing a quantitative theoretical description has been challenging. The article also highlights the different types of experimental measurements that have been used to study CISS, including measurements of spin-dependent transmission, tunneling currents, magnetization, and magnetic domains. The article concludes by discussing the potential applications of CISS in spintronics, electrochemistry, and biology, and expresses optimism that further research will reveal the mechanism behind the CISS effect. [Extracted from the article]

Covalent bonding interactions determine the energy–momentum (E–k) dispersion (band structure) of solid-state materials. Here, we show that noncovalent interactions can modulate the E–k dispersion near the Fermi level of a low-dimensional nanoscale conductor. We demonstrate that low energy band gaps may be opened in metallic carbon nanotubes through polymer wrapping of the nanotube surface at fixed helical periodicity. Electronic spectral, chiro-optic, potentiometric, electronic device, and work function data corroborate that the magnitude of band gap opening depends on the nature of the polymer electronic structure. Polymer dewrapping reverses the conducting-to- semiconducting phase transition, restoring the native metallic carbon nanotube electronic structure. These results address a long-standing challenge to develop carbon nanotube electronic structures that are not realized through disruption of π conjugation, and establish a roadmap for designing and tuning specialized semiconductors that feature band gaps on the order of a few hundred meV. [ABSTRACT FROM AUTHOR]

Chiral perovskite nanoparticles and films are promising for integration in emerging spintronic and optoelectronic technologies, yet few design rules exist to guide the development of chiral material properties. The chemical space of potential building blocks for these nanostructures is vast, and the mechanisms through which organic ligands can impart chirality to the inorganic perovskite lattice are not well understood. In this work, we investigate how the properties of chiral ammonium ligands, the most common organic ligand type used with perovskites, affect the circular dichroism of strongly quantum confined CsPbBr3 nanocrystals. We show that aromatic ammonium ligands with stronger electron-donating groups lead to higher-intensity circular dichroism associated with the lowest-energy excitonic transition of the perovskite nanocrystal. We argue that this behavior is best explained by a modulation of the exciton wavefunction overlap between the nanocrystal and the organic ligand, as the functional groups on the ligand can shift electron density toward the organic species-perovskite lattice interface to increase the imprinting. [ABSTRACT FROM AUTHOR]

We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is given by a position-dependent phase, eiWx. We consider both equilibrium and nonequilibrium initial conditions. We show that, for this model, all equilibrium results are completely invariant to the sign of W (to infinite order). However, the nonequilibrium results do depend on the sign of W, suggesting that photo-induced electron transfer dynamics with spin–orbit coupling can exhibit electronic spin polarization (at least for some time). [ABSTRACT FROM AUTHOR]

This work presents new results and summarizes literature results on the chiral induced spin selectivity (CISS) effect observed for amino acids, peptides, and DNA. To facilitate robust comparisons between measurements of different types and by different groups, we propose a convention for describing the spin‐dependent properties of chiral materials and apply it in the discussion. Different phenomena known to affect the sign and magnitude of the spin polarization are described and critically analyzed, including: the molecule's orientation, the molecule's dipole moment direction with respect to the electron propagation direction, the molecular length, the molecule/substrate interface, and the role of the molecule's secondary structure. Lastly, we identify open key questions about spin‐filtering by biomolecules at interfaces. [ABSTRACT FROM AUTHOR]

Controlled reduction of oxygen is important for developing clean energy technologies, such as fuel cells, and is vital to the existence of aerobic organisms. The process starts with oxygen in a triplet ground state and ends with products that are all in singlet states. Hence, spin constraints in the oxygen reduction must be considered. Here, we show that the electron transfer efficiency from chiral electrodes to oxygen (oxygen reduction reaction) is enhanced over that from achiral electrodes. We demonstrate lower overpotentials and higher current densities for chiral catalysts versus achiral ones. This finding holds even for electrodes composed of heavy metals with large spin–orbit coupling. The effect results from the spin selectivity conferred on the electron current by the chiral assemblies, the chiral-induced spin selectivity effect. [ABSTRACT FROM AUTHOR]

Byline: Spiros S. Skourtis, Department of Physics, University of Cyprus, Nicosia 1678, Cyprus; email: skourtis@ucy.ac.cy; David H. Waldeck, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260; email: dave@pitt.edu; David N. Beratan, Departments of Chemistry and Biochemistry, Duke University, Durham, North Carolina 27708; email: david.beratan@duke.edu Keywords: coupling fluctuations, tunneling pathways, inelastic tunneling, pathway coherence, solvent dynamical effects, water-mediated tunneling Abstract Central to theories of electron transfer (ET) is the idea that nuclear motion generates a transition state that enables electron flow to proceed, but nuclear motion also induces fluctuations in the donor-acceptor (DA) electronic coupling that is the rate-limiting parameter for nonadiabatic ET. The interplay between the DA energy gap and DA coupling fluctuations is particularly noteworthy in biological ET, where flexible protein and mobile water bridges take center stage. Here, we discuss the critical timescales at play for ET reactions in fluctuating media, highlighting issues of the Condon approximation, average medium versus fluctuation-controlled electron tunneling, gated and solvent relaxation controlled electron transfer, and the influence of inelastic tunneling on electronic coupling pathway interferences. Taken together, one may use this framework to establish principles to describe how macromolecular structure and structural fluctuations influence ET reactions. This framework deepens our understanding of ET chemistry in fluctuating media. Moreover, it provides a unifying perspective for biophysical charge-transfer processes and helps to frame new questions associated with energy harvesting and transduction in fluctuating media.

Chirality in life has been preserved throughout evolution. It has been assumed that the main function of chirality is its contribution to structural properties. In the past two decades, however, it has been established that chiral molecules possess unique electronic properties. Electrons that pass through chiral molecules, or even charge displacements within a chiral molecule, do so in a manner that depends on the electron's spin and the molecule's enantiomeric form. This effect, referred to as chiral induced spin selectivity (CISS), has several important implications for the properties of biosystems. Among these implications, CISS facilitates long-range electron transfer, enhances bio-affinities and enantioselectivity, and enables efficient and selective multi-electron redox processes. In this article, we review the CISS effect and some of its manifestations in biological systems. We argue that chirality is preserved so persistently in biology not only because of its structural effect, but also because of its important function in spin polarizing electrons. [ABSTRACT FROM AUTHOR]

An investigation is conducted to elucidate the photoinduced electron-transfer kinetics and charge-transfer emission spectra of two U-shaped DBA molecules in various aromatic solvents of varying polarities by measuring electron-transfer rates. The empirical outcomes exhibit the operation of the through-pendant-group mechanism of electron transfer in the pendant-containing U-shaped systems of the U-shaped DBA molecules.

Horse heart cytochrome c is immobilized on four different self-assembled monolayer (SAM) films and cyclic voltammetry is used to analyze the electron tunneling kinetics in different assemblies as a function of the ionic strength of the buffer solution. The observed inhomogeneity indicates that a distribution of cytochrome c orientations and hence a distribution of electron transfer rate constants exists.

Theoretical analysis of nonadiabatic electron-transfer reactions in molecules usually assumes that electron amplitude propogates coherently from the reductant to the oxidant via covalent and noncovalent coupling pathways. An attempt is made to show that when the tunneling electron excites local bridge vibrations (inelastic tunneling), the excitation 'labels' the physical pathway traversed.

The electron-transfer rate constant is measured in two U-shaped donor-bridge-acceptor molecules over a wide range of temperature in acetonitrile and N-methylacetamide (NMA). The electron-transfer rate at high temperature can be well described by a nonadiabatic model of the reaction but at low temperatures the rate in NMA becomes controlled by the solvent.

A set of molecular dynamics (MD) simulations (20 ns of total reported simulation time) of a beta-cyclodextrin (betaCD) molecule confined inside the lumen of the alpha-hemolysin channel (alphaHL) is presented. The equilibrated configurations with betaCD residing in the vicinity of Met 113 with its wider rim oriented toward the trans side of the membrane were found to be the most favorable in terms of both interaction and binding free energies as per results.

The unusual (super 57)Fe Mossbauer quadrupole splittings and isomer shifts in 2- and 3- coordinate high-spin iron-thiolate complexes and model systems can be calculated using spin unrestricted DFT methods as long as large-scale basic sets and structural models are used as per description. An MO analysis provides a detailed picture of the origin of the small delta E(sub q) values seen in the 3-coordinate complexes.

The electron exchange kinetics of horse heart cytochrome c (Cyt c) at 4,4' -bipyridyl- and 4,4' -bipyridyl- disulfide-modified Au electrodes is studied for the first time under variable pressure conditions (up to 150 MPa), by using fast scanning cyclic voltammetry. An extended comparative analysis revealed both the similarities and fine differences between the elementary charge-transfer processes involving low molecular weight redox-active metal complexes and this redox protein.

Conventional electrochemical techniques are applied to the electron transfer of cytochrome c protein immobilized on the surface of SAM modified electrodes. Chemical control of adsorption allows the accurate determination of heterogeneous unimolecular rate constants for the electron exchange between the SAM modified metal electrode and the cytochrome c.

The electron transfer is a basic chemical process that has a lot of scientific significance and studies are conducted to evaluate the electron tunneling efficiency between electron donor and acceptor groups using noncovalent molecular contacts. Experimental electron transfer rate constants and reaction free energies are used to calibrate a molecular based model that defines the solvation energy.

A novel strategy for the immobilization of cytochrome C on the surface of chemically modified electrodes is demonstrated and used to investigate the protein's electron-transfer kinetics. The ability to absorb the redox active cytochrome C to the surface of SAM-coated gold electrodes in a restricted geometry is demonstrated.

The transition between the solvent-controlled regime (in which the electron-transfer rate constant depends on the solvent friction) and the nonadiabatic electron-transfer limit was observed for the Au/Fe(CN)(sub 6)(super 3-/4-) redox system by variation of electronic coupling strength. In the nonadiabatic regime the distance dependence of the electronic of the electronic coupling decay is 1.04 degreeA(super -1), and its extrapolated value at the closest electrode-reactant distance is 3.5 kcal mol(super -1).

Picosecond optical calorimetric and fluorescent studies of the photoisomerization of tetraphenylethylene help understand the structure-kinetic and structure-energy relations in the excited twisted state. These studies indicate the presence of three excited states, which provide a pathway for the potential energy surface along the photoisomerization coordinate.