Abstract Hetero-cycloaddition reactions are powerful, atom-economical strategies for the rapid construction of heterocyclic frameworks from readily available building blocks. Over the past two decades, advances in photochemistry, photocatalysis, and modern excitation strategies have driven remarkable developments in the field. By accessing electronically excited states, light enables cycloaddition pathways inaccessible under classical thermal conditions, providing access to reactive radical, ionic, or excited-state intermediates under mild conditions. Technological advances in light sources and photocatalyst design have improved reaction efficiency, site-, regio-, and stereoselectivity, while considerably expanding the accessible chemical space. Beyond established hetero-[2 + 2], hetero-(3 + 2), and hetero-[4 + 2] processes, new reaction classes, including π–σ hetero-cycloadditions exploiting strained small-ring systems, have emerged as powerful approaches to structurally complex saturated scaffolds of increasing relevance in medicinal chemistry. In this Review, we critically examine the evolution of photochemical hetero-cycloadditions from 2000 to 2026, discussing fundamental concepts and terminology, cycloaddition classes, heterocyclic targets, and activation mechanisms. We highlight the conceptual advances that have shaped modern photochemical hetero-cycloaddition chemistry and conclude by discussing current limitations and future directions for the field.
Abstract Nanocrystalline metal halide perovskites are promising light emitters for light-emitting diodes (PeLEDs) because they suppress the intrinsic problem of exciton dissociation through charge confinement within nanocrystalline domains. Although these nanostructures have enabled high-emission efficiencies, such confinement strategies typically result in significantly reduced charge transport. This limitation is attributed to numerous grain boundaries, which induce severe charge carrier scattering and trapping, alongside insulating organic ligands typically introduced for defect passivation and size reduction. Poor charge transport increases the required operating voltage and accelerates device degradation pathways under an electrical bias, leading to limited operational lifetimes. This Review examines material design strategies intended to mitigate the competition between charge confinement and transport across various nanocrystalline perovskites. Specifically, we investigate fundamental crystal nucleation and growth mechanisms and evaluate methods to optimize grain size, aiming to minimize the grain boundary to increase charge transport while maintaining charge confinement. Passivation strategies for defect states are also evaluated, emphasizing the engineering of organic ligands to enhance their electrical conductivity while maximizing the passivation efficacy. In addition, the integration of core/shell architectures is discussed as a promising strategy. By controlling the shell composition, these structures promote efficient charge transport while maintaining high radiative recombination rates. Together, these material design strategies aim to overcome the confinement and transport trade-offs in PeLEDs.
Abstract Chiral medium-sized rings, defined herein as 7- to 11-membered cyclic frameworks, are common in bioactive molecules and occupy an important but still underexplored region of drug-like chemical space. Their asymmetric synthesis remains formidably challenging, as conformational flexibility, transannular interactions, and unfavorable entropic and enthalpic factors collectively complicate ring formation and stereocontrol. In recent years, palladium- and iridium-catalyzed asymmetric dipolar cycloadditions and related cascade processes have emerged as effective strategies for building structurally diverse and stereochemically complex medium-sized rings. As such, this review aims to summarize the advances in this emerging field from the perspectives of metal identity, precursor class, and dipole-generation mode, with emphasis on their effects on chemo-, regio-, diastereo-, and enantioselectivity. We also highlight the distinct yet complementary features of Pd and Ir catalysis, as well as current limitations in generality, selectivity, and substrate scope. By combining mechanistic insight with representative applications, this review aims to define the foundations, boundaries, and future opportunities of this rapidly evolving area.
Controlling the energetic landscape of metal halide perovskite solar cells is crucial for optimizing device efficiency and stability, as well as enabling new architectures beyond conventional layered designs. While band alignment criteria are key determinants of performance in organic photovoltaic devices, they are often insufficient for perovskites due to their high charge carrier density, mobile ions, and soft lattice structure. A deep understanding of the electronic structure of the perovskite and the contacting layers remains an active area of research and requires expertise in the characterization techniques. In this review, we analyze how interfacial energetics influence charge extraction, the formation of energy barriers, interfacial recombination, and ion migration, highlighting the unique challenges posed by the soft ionic lattice of metal halide perovskites. To this end, we provide a comprehensive overview of experimental techniques for probing energetic alignment, emphasizing their operating principles, limitations, and emerging in situ variants. Building on these insights, we discuss strategies for controlling the interfacial energetics of perovskite solar cells, ranging from interfacial layers and dipolar modifiers to electrical doping. Finally, we explore the device architectures that eliminate the need for charge-selective layers. Together, these insights establish a framework for understanding and engineering the energetic landscape of metal halide perovskite-based devices, linking fundamental semiconductor physics with practical strategies for future perovskite technologies.
Hybrid metal halides have experienced rapid growth in research activity, achieving remarkable advances over the past decade and a half. This expansion stems from valuable traits including synthetic and optoelectronic tunability, high absorption coefficients, solution processability, and high defect tolerance. Studies on these materials have expanded from 3D perovskites to include their low- dimensional 2D counterparts, whose performance and improved stability have made them model systems for various applications, yet this progress has only begun to scratch the surface of structural possibilities. Other low-dimensional metal halides, including perovskitoids and nonperovskite structures, remain far less explored despite offering immense structural diversity and functional potential. In this Review, we provide an updated, integrative perspective on these overlooked systems. We begin by describing synthetic strategies for low-dimensional metal halides, covering both established and emerging approaches. We then examine structural motifs, illustrating how octahedral connectivity defines dimensionality and lattice architecture. Optoelectronic properties follow, focusing on how composition, distortion, and the organic spacer chemistry modulate optical and electronic behavior in these materials. A dedicated section highlights optoelectronically active organics. Finally, we address stability and degradation mechanisms and feature recent advances and representative case studies, including their translation into thin films and next-generation optoelectronic and radiation-detection devices. The advances achieved to date reveal general principles that connect dimensionality, connectivity, and organic-inorganic interactions across the full landscape of hybrid metal halides, while also exposing the limits of current predictive understanding. The remaining challenge is to translate these qualitative insights into design rules that reliably link structure to function and guide the deliberate creation of next-generation low-dimensional materials.
