Inspired by the success of graphene, two-dimensional (2D) materials have been at the forefront of advanced (opto-)nanoelectronics and energy-related fields owing to their exotic properties like sizable bandgaps, Dirac fermions, quantum spin Hall states, topological edge states, and ballistic charge carrier transport, which hold promise for various electronic device applications. Emerging main group elemental 2D materials, beyond graphene, are of particular interest due to their unique structural characteristics, ease of synthetic exploration, and superior property tunability. In this review, we present recent advances in atomic-scale studies of elemental 2D materials with an emphasis on synthetic strategies and structural properties. We also discuss the challenges and perspectives regarding the integration of elemental 2D materials into various heterostructures.

Ultrafast excitation of nanoparticles can excite the acoustic vibrational modes of the structure that correlate with the expansion coordinates. These modes are frequently seen in transient absorption experiments on metal nanoparticle samples and occasionally for semiconductors. The aim of this review is to give an overview of the physical chemistry of nanostructure acoustic vibrations. The issues discussed include the excitation mechanism, how to calculate the mode frequencies using continuum mechanics, and the factors that control vibrational damping. Recent results that demonstrate that the high frequencies inherent to the acoustic modes of nanomaterials trigger a viscoelastic response in surrounding liquids are also discussed, as well as vibrational coupling between nanostructures and mode hybridization within the nanostructures. Mode hybridization provides a way of manipulating the lifetimes of the acoustic modes, which is potentially useful for applications such as mass sensing.

Friction is a phenomenon that manifests across all spatial and temporal scales, from the molecular to the macroscopic scale. It describes the dissipation of energy from the motion of particles or abstract reaction coordinates and arises in the transition from a detailed molecular-level description to a simplified, coarse-grained model. It has long been understood that time-dependent (non-Markovian) friction effects are critical for describing the dynamics of many systems, but that they are notoriously difficult to evaluate for complex physical, chemical, and biological systems. In recent years, the development of advanced numerical friction extraction techniques and methods to simulate the generalized Langevin equation has enabled exploration of the role of time-dependent friction across all scales. We discuss recent applications of these friction extraction techniques and the growing understanding of the role of friction in complex equilibrium and nonequilibrium dynamic many-body systems.

This is a recollection of my scientific trajectory. When I look back, I consider myself to be very fortunate for being able to do something I love and on topics of my own will. I am not a competitive person and tend to shy away from the limelight. Nonetheless, I survived in my profession and eventually made some modest contributions, which are beyond what I would have expected. We often forget about the human aspect of scientific endeavor. After all, science is done by individuals; humans have emotions and make mistakes. The frustrations of failures, the joys of finding problems and solutions to them, and the passion for fulfilling curiosity are all parts of this endeavor. Throughout the years, many people-mentors, students, postdocs, collaborators, and colleagues-have accompanied me in this exciting and fruitful journey, for which I am deeply grateful and feel very lucky to have them.

Reaction coordinates (RCs) are the few essential coordinates of a protein that control its functional processes, such as allostery, enzymatic reaction, and conformational change. They are critical for understanding protein function and provide optimal enhanced sampling of protein conformational changes and states. Since the pioneering work in the late 1990s, identifying the correct and objectively provable RCs has been a central topic in molecular biophysics and chemical physics. This review summarizes the major advances in identifying RCs over the past 25 years, focusing on methods aimed at finding RCs that meet the rigorous committor criterion, widely accepted as the true RCs. Notably, the newly developed physics-based energy flow theory and generalized work functional method provide a general and rigorous approach for identifying true RCs, revealing their physical nature as the optimal channels of energy flow in biomolecules.

This review provides focused coverage of the photophysical properties of noncanonical and synthetic nucleobases reported over the past decade. It emphasizes key research findings and physical insights gathered for prebiotic and fluorescent nucleobase analogs, sulfur- and selenium-substituted nucleobases, aza-substituted nucleobases, epigenetic nucleobases and their oxidation products, and nucleobases utilized for expanding DNA/RNA to reveal central structure-photophysical property relationships. Further research and development in this emerging field, coupled with machine learning methods, will enable the effective harnessing of nucleobases' modifications for applications in biotechnology, biomedicine, therapeutics, and even the creation of live semisynthetic organisms.

The unique properties of ionic liquids (ILs) result from the tunable mélange of Coulomb interactions, hydrogen bonding, and dispersion interactions among the constituent ions. In hydroxy-functionalized ILs, local and directional hydrogen bonds (H-bonds) lead to the anticipated formation of ion pairs but also to the elusive formation of cationic clusters. Here, we review how hydrogen-bonding motifs in the bulk liquid and gas phase of hydroxy-functionalized ILs shed light on the general nature of hydrogen bonding. Infrared spectroscopy, nuclear magnetic resonance, neutron diffraction, and molecular dynamics simulations provide information about the structure, strength, and dynamics of cationic clusters in the bulk liquid ILs. Cryogenic ion vibrational predissociation (CIVP) spectroscopy along with density functional theory calculations has established a clear picture about the specific contacts within isolated H-bonded cationic clusters formed in the gas phase. This information from experiment, simulation, and theory provides a fundamental understanding of hydrogen bonding between the ions in ILs.

The movement of charges through a chiral medium results in a spin-polarized charge current. This phenomenon, known as the chirality-induced spin selectivity (CISS) effect, enables control over spin populations without the need for magnetic components and operates at room temperature. CISS has been discovered in a range of chiral media and most prominently studied in chiral organic molecular species. Chiral hybrid organic-inorganic perovskite semiconductors combine the unique and functional aspects of inorganic semiconductors with chiral molecules. The inorganic component borrows the homochirality of the organic component to yield a unique family of highly tunable chiral semiconductors, where the enantiomeric purity is defined by the organic component. Semiconductors already form the backbone of modern-day technologies. Adding chirality and control over spin through CISS provides new avenues for creative technological development. This review is intended to be an introduction to these unique systems and the demonstrations of CISS and spin control.

Recent studies on ozone photodissociation in the Hartley and Huggins bands have provided new insights into the dissociation dynamics and product state distributions. A Λ-doublet propensity in the photodissociation has been identified through experiment and theory as the origin of the oscillatory O2(a1Δg) rotational distributions and provides a promising diagnostic for determining the relative contributions of 3A' and 3A″ states in Huggins band spin-forbidden processes. Recent experiments on spin-forbidden dissociation have provided detailed information about the vibrational and rotational distributions of the O2 products and the branching ratios between the O2 electronic states, serving as a motivation for high-level theory.

As a nonlinear optical process, sum frequency generation (SFG) requires noncentrosymmetry across multiple length scales, ranging from individual molecular functional groups to their arrangements in space. This principle makes SFG not only intrinsically sensitive to molecular species at surfaces but also useful for studying 3D structures of crystalline biopolymers in natural materials. Examples of such biopolymers are cellulose, starch, and chitin in the polysaccharide family and collagen, silk, and keratin in the fibrous protein family. These biopolymers are noncentrosymmetric at multiple length scales, with chirality at the molecular scale, unit cell structure at the nanoscale, and crystallite orientation and polarity at the mesoscale; thus, they are SFG active. In this review, we describe how SFG can be used to determine nano- to mesoscale polarity and orientational orders of crystalline biopolymers interspersed in natural materials containing the same or similar biopolymers in amorphous states, which cannot be obtained with other characterization methods.