Chirality can be transmitted between various media and size scales, from spinning elementary particles or chiral molecules to mesoscopic and macroscopic structures through electromagnetic fields or emergent spin structures. These transmission processes. The transmission mechanism of chirality information, which can be expressed in the intra-inter-atomic/molecular interaction, is extremely complex and never ceases to fascinate scientists. When investigating systems spanning a large size range, hierarchical nanostructures based on molecular assemblies represent promising structures that allow us to fill in the gap that is difficult to assess from both top-down and bottom-up approaches.

For several decades, based on the molecular assembly, we have developed helical nanostructures with controlled sizes of the order of 10-100 nm and handedness, which have shown very promising properties not only as fundamentally interesting shaped objects with intriguing properties but also as helical platforms transferring the chiral information between very small to large objects and vice-versa, from electrons, atoms, molecules or large polymers and even nanoparticles. Through such interaction, we have shown exciting examples of their use in chiral induction, amplification, crystallisation, reaction, and chiral recognition.

Hybrid organic–inorganic perovskites have emerged as exceptional materials for optoelectronic and energy conversion devices [1]. Recently, chiral hybrid perovskites, which incorporate chiral organic ligands into the inorganic framework, have attracted increasing attention as promising chiroptoelectronic systems with potential applications in optoelectronics, spintronics, and beyond [2]. The chirality and associated chiroptical responses in these materials are attributed to a chiral bias originating from the chiral organic ligands, which propagates through the inorganic framework, influencing the geometry of the entire hybrid perovskite structure [3]. Insights from soft materials design offer further opportunities to tailor and optimize these properties [4].

Modern multiscale modeling and simulation techniques have now reached unprecedented levels of accuracy, enabling the efficient design of chiral materials and the precise optimization of their chiroptical properties. In this discussion, I will present simulation workflows developed over the years to predict the circular dichroism (CD) and circularly polarized luminescence (CPL) of soft [5] and hybrid materials [6]. Enhanced sampling simulations, particularly through parallel bias metadynamics, in conjunction with ab-initio molecular dynamics (AIMD) based on density functional theory (DFT) methods and their time-dependent extensions, were employed to investigate the structure, dynamics, and chiroptical spectra, with a focus on CD and CPL.This simulation strategy enables the prediction of how non-covalent interactions in excited states can contribute to the generation of CPL spectra and the associated dissymmetry factors.

References

[1] Grancini, Nazeeruddin. Nat. Rev. Mater. 4: 2019, 4.

[2] Pietropaolo, Mattoni, Pica, Fortino, Schifino, Grancini. Chem 8: 2022, 1231.

[3] Long, Sabatini, Saidaminov, Lakhwani, Rasmita, Liu, Sargent, Gao. Nat. Rev. Mater. 5: 2020, 423.

[4] Albano, Pescitelli, Di Bari. Chem. Rev. 120: 2020, 10145.

[5] Wu, Pietropaolo, Fortino, Shimoda, Maeda, Nishimura, Bando, Naga, Nakano. Angew. Chem. Int. Ed. 61: 2022, e202210556.

[6] Fortino, Mattoni, Pietropaolo. J. Mater. Chem. C 11: 2023, 9135.

Hybrid organic–inorganic perovskites (HOIPs) have emerged as excellent materials for solar cell applications. Indeed, their extreme tunability and facile synthesis have opened the door to many new applications. Chiral HOIPs are attracting great interest as promising frameworks for chiroptoelectronics as well as spintronics applications.^[1,2] The chiroptical properties observed in chiral HOIPs can be explained understanding the chirality transfer from the chiral organic molecules to the achiral inorganic octahedra. A key element of the chirality transfer mechanism involves the distortion of the coordination geometry of the inorganic octahedra induced by the presence of chiral ligands.In this study, we propose a tailored simulation workflow based on Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT)^[3] to theoretically explore the chirality transfer mechanism and the chiroptical properties of chiral HOIPs. To this aim, we investigate the chiroptical response of lead- and tin-based 2D chiral perovskites, specifically 2D R- and S-(MBA+)2PbI4^[4] and R- and S-(MBA+)2SnI4.^[5] We explore the most impactful factors influencing their Circular Dichroism (CD) signals through ab-initio molecular dynamics simulations and the analysis of the density of electronic states (DOSs). Our findings reveal that the relevant chiroptical features are linked to a chirality transfer event driven by a metal–ligand overlap of electronic levels. This effect is more evident for tin-based chiral perovskites showing higher excitonic coupling.

Semi-artificial photosynthesis interfaces biological catalysts with synthetic materials such as electrodes or light absorbers to overcome limitations in natural and artificial photosynthesis. The benefit of using biocatalysts in catalytic CO2 utilisation is their electrochemical reversibility that allows operation at very low overpotentials with high selectivity, in addition to their chirality that enables enantioselective synthesis. This presentation will summarise my research group’s progress in integrating the CO2 reducing enzyme formate dehydrogenase into bespoke hierarchical 3D electrode scaffolds and the exploitation in solar-powered catalysis towards the synthesis of chiral organics via enzymatic cascade reactions. I will present the electrochemical features and characterisation of the biocatalyst-material interface and provide my team's understanding of the electrochemical properties of the immobilised enzymes. This insight allows the wiring of the biocatalyst into electrocatalytic schemes, photoelectrochemical devices and photocatalytic systems for unique CO2 utilisation reactions. The fundamental insights gained by integrating isolated CO2-utilising enzymes in electrodes will be presented and the case be made that this enzyme allows opening a solar-to-chemical conversion space that is currently not accessible with purly synthetic or biological systems.

Monocrystalline plasmonic nanostructures (e.g. Au, Ag, Cu, and Al) because of their well-defined crystallographic surfaces and low ohmic losses exhibit unique optical [1] and catalytic [2] properties, rendering them promising candidate catalysts for photo-electrochemistry and solar fuel production [3]. Importantly, high-definition monocrystalline nanostructures with well-controlled optical absorption characteristics can be used to obtain a fundamental understanding of the role of hot carriers in plasmonic photocatalysis [4]. However, despite many studies on the optical properties of high-definition monocrystalline gold (Au) nano-antennas, photocatalytic performance of these array structures has not been studied so far due to the challenges associated with fabricating cm-scale array structures and the incapability of the conventional photoelectrochemical systems in detecting signals from tiny reactions on um-scale array structures. In this work, we report on light-assisted scanning electrochemical microscopy (photo-SECM) studies of a series of um-scale Au nano-antenna arrays fabricated by electron beam lithography on high-aspect ratio Au micro-flakes [5] on a TiO₂ and p-GaN semiconducting substrates [6,7]. Photo-SECM experiments were performed to quantify the wavelength-dependent photochemical response and internal quantum efficiency of the plasmonic-redox molecule systems. Combining experimental data with numerical/ab-initio modelling, we disentangled the roles of hot carrier generation, transport, and injection at both solid/solid and solid/liquid interfaces. We determined the energy-dependent injection efficiency of hot carriers and identified their transfer mechanisms at the metal/electrolyte interface, proving that they are highly impacted by the metal/molecule interaction. We discovered a tunneling hole transfer to the molecule in the Au/TiO₂ photoanode and a combination of tunneling and direct electron transfer to the molecule in the Au/p-GaN photoanode systems. This work provides an unprecedented understanding of the interplay of hot-carrier-driven processes, shedding light on the important mechanisms governing the transport and injection of hot carriers across interfaces in hot-carrier-driven photocatalytic systems.

The chiral induced spin selectivity (CISS) effect means that electron transport through chiral systems is spin dependent. [1] The effect was found to exist not only on molecular scale but also in crystals when the scale of the spin transport exceeds microns. In addition, in many cases, the effect was found to increase with increasing temperatures. Recent studies on electron transfer (ET) through proteins established that the effect is indeed long range and with extremely high spin selectivity, reaching 100%.[2]

Experimental results obtained on long range CISS effect will be presented and the dilemma they present will be discussed. Since the CISS effect involves also charge transfer, its mechanism must reflect the ET process. Experimental results will be presented that indicate that the CISS effect cannot be explained based on a single electron and Born-Oppenheimer based models.

It will be shown that models that are not based on these approximations can provide qualitative understanding of the CISS, although real first principle calculations remain a major challenge.

Keywords: Chirality, spin, electron transport

R. Naaman, Y. Paltiel, D. H. Waldeck, Annu. Rev. Biophys. 2022, 51, 99.

S. Ghosh, K Banerjee-Ghosh, D. Levy, D. Scheerer, I. Riven, J. Shin, H. B. Gray, R. Naaman, G. Haran, PNAS 119,  2022, e2204735119.

Electrocatalytic water splitting is generally regarded as the most environmental-friendly and sustainable pathway for green hydrogen production. However, the energy efficiency of water electrolysis is hampered mostly by the anodic process, where the sluggish oxygen evolution reaction (OER) requires excessively high overpotentials to proceed at relevant current densities. This high overpotentials needed are partly due to complexity of this 4e^– process requiring the generation of a O₂ molecule with ground triplet state. Because of this, spin polarization upon the catalytic entities has been proposed to improve the efficiency of the process, in order to favor parallel spin alignment in the product.

One successful strategy towards this aim has been realized through the chiral-induced spin selectivity (CISS) effect [1]. Following this strategy, improved OER kinetics are promoted when a catalytic surface is decorated with chiral organic molecules, which has been assigned to the spin-filtering power of the enantiopure molecules as mediators in the charge transfer processes [2]. Another plausible strategy to achieve improved OER kinetics points towards the use of external magnetic fields, which are able to favor spin alignment of open shell radicals to form an open shell O–O bond [3].

In this talk we will present our latest results following these two different approaches to accelerate the OER anodic reaction during water splitting. We will introduce our strategies for the design of the catalysts, as enantiopure or magnetically active sites; their structural, magnetic and electrochemical characterization; up to their implementation into full cell electrolyzers as proof-of-concept for future exploitation of these promising phenomena for enhanced OER electrocatalysis.

We have an ongoing interest in the development of conjugated chiral molecules which can emit and detect circularly-polarised (CP) light within thin film materials and in organic electronic devices. CP light is central to many applications, including data storage, quantum computation, biosensing, environmental monitoring and display technologies. Such technologies require the generation of device compatible materials and clear understanding of the chiroptical mechanisms at play [1], [2].

Using a range of chiral materials - helicenes, fullerenes and polymers - this talk will give an overview of our strategies to maximise the selectivity of such chiral-optical responses through molecular design, materials processing and device architecture. Key and suprising results will be showcased and discussed, including the the role of polymer supramolecular assembly in large chiroptical responses [3], the potential for amplication of dissymmerty through energy transfer [4] and the observation of anomolous circularly polaized electroluminescence [5]. Recent results will be discussed that allow for an interplay between natural and anomolous mechanisms in circularly polaized electroluminescence providing additional levels of control.

Despite the enormous advances in producing green electrons from solar cells to address our current energy crises, the future society will also require sustainable fuels to move forward. Producing these sustainable fuels necessitates not only the use of renewable energy sources to power the processes but also the design of synthesis routes that can reduce carbon emissions [1]. In this context, the sun stands out as one of the most potent and explored sources for generating green fuels, specifically solar fuels. Harnessing the incoming photons from the sun to power electro- or photo-catalysts involves engineering surfaces or nanomaterials capable of effectively utilizing these photons to activate chemical bonds [2, 3].

This talk will provide an overview of our current efforts to enhance the production of solar fuels using plasmonic and photonic structures. Plasmonic structures exploit the oscillations of free electrons in metallic nanostructures when exposed to light, thereby enhancing light absorption and scattering [4]. This leads to increased efficiency in capturing solar energy and focusing it at the nanoscale, which enhances the electromagnetic field and facilitates chemical reactions [5]. Photonic structures, on the other hand, manipulate the flow of light at the nanoscale, improving light-matter interactions. They enhance the absorption and utilization of solar photons through improved light management, such as in photonic crystals and metamaterials, which can control light propagation to maximize interaction with catalytic surfaces [6].

Key principles for designing the next generation of sunlight-activated catalysts will be discussed, including material selection, nanostructure engineering, and the integration of renewable energy sources. By addressing these challenges, we can develop more efficient systems for converting solar energy into chemical fuels. This talk aims to highlight the significant advancements and future potential of plasmonic and photonic structures in the realm of solar fuel production, drawing insights from current research and existing literature to outline the path forward in this critical area of sustainable energy development.

The oxygen evolution reaction (OER, 1) is critical for hydrogen production via water electrolysis. However, it has notably sluggish kinetics. It has been proposed that part of the high overpotential required for oxygen formation is due to the spin restrictions necessary for oxygen formation in its fundamental triplet state [1].

 4 OH^- → O₂ + 2 H₂O + 4 e^-            Eº=1.23 V            (1)

We investigated how spin alignment can enhance the OER and reduce the competing water oxidation reaction that forms H₂O₂. Specifically, we explored enhancing the OER by modifying state-of-the-art electrodes with chiral molecules, leveraging the chiral-induced spin selectivity (CISS) effect [2,3]. By comparing the electrocatalytic performance of electrodes modified with different compositions of chiral molecules, we found that the OER enhancement is significantly influenced by the presence of homochiral domains. Furthermore, we confirmed the spin-selectivity effect by observing a reduction in H₂O₂ formation on mesoporous hybrid systems.[4] Additionally, we studied the impact of static magnetic fields on reaction kinetics and mass transport using key electrocatalysts.[5] Our findings offer a strategy to optimize spin-enhanced OER, which can be easily extended to boost multiple key electrocatalytic reactions that involve spin selective intermediates.

Electrocatalytic water splitting is well suited for the production of hydrogen as a clean and renewable energy carrier to alleviate the current energy crisis. However, the sluggish kinetics of the anodic oxygen evolution reaction (OER), which involves the generation of triplet oxygen from singlet water on the electrocatalyst surface, results in a low overall energy efficiency and necessitates the use of high voltages to drive the spin transition. Herein, we harnessed the potential of topological chiral semimetals (RhSi, RhSn, and RhBiS) and their spin-polarized Fermi surfaces to promote the spin-dependent electron transfer in OER and overcome the volcano-plot limitation of conventional catalysts. The OER activity increases in the order of RhSi < RhSn < RhBiS, following the trend of spin-orbit-coupling (SOC). The chiral single crystals of RhSi, RhSn, and RhBiS exhibited higher OER activities than those of achiral crystals of RhTe₂, RhTe, and the benchmark catalyst of RuO₂. Especially, the specific activity of RhBiS exceeded that of RuO₂ by two orders of magnitude. Our work reveals the pivotal roles of chirality and SOC in spin-dependent catalytic processes, facilitating the design of ultra-efficient chiral catalysts. Therefore, in future endeavors, the development of top-performing catalysts could encompass spin polarization as a fundamental property for chiral materials with SOC serving as a valuable descriptor.

The visible-light excitation of plasmonic nanostructures is now well known to induce catalytic reactions that are not otherwise observed in the dark. I will describe how catalysts based on plasmonic nanoparticles are allowing light to be used as a redox equivalent in chemical reactions, for driving non-equilibrium chemical processes, for modifying product selectivity, for photosynthesizing fuels, and for boosting electrochemical conversions. One prime example discovered in my group is the conversion of carbon dioxide to hydrocarbons on gold nanoparticles driven by electron–hole pairs generated by plasmonic excitation. This photochemistry constitutes much more than photoenhanced catalysis: rather chemical potential is harvested from plasmonic excitations and stored in the form of energy-rich bonds. The chemical potential is a linear function of the concentration of light, as I will show using a simple model and experimental findings from a diverse set of reactions. However, conversions driven by plasmonically generated carriers can suffer from thermodynamic and efficiency limits. I will describe how such limits can be overcome.

The chiral-induced spin selectivity (CISS) effect has recently gained significant attention in the field of spintronics. The remarkably high polarization efficiency of chiral molecules via the CISS effect paves the path toward novel, sustainable hybrid chiral molecule magnetic applications. While research has predominantly focused on transport properties so far, in our work, we explore spintronic phenomena at hybrid chiral molecule magnetic interfaces to elucidate the underlying mechanisms of the chiral-induced spin selectivity effect. For this, we investigate the interfacial spin-orbit coupling in chiral molecule/metal thin film heterostructures by probing the chirality and spin-dependent spin-to-charge conversion. For this, we inject a pure spin current via spin pumping and investigate the spin-to-charge conversion at the hybrid chiral interface. Notably, we observe a chiral-induced unidirectionality in the conversion [1]. Furthermore, angle-dependent measurements reveal that the spin selectivity is maximum when the spin angular momentum is aligned with the molecular chiral axis. Our findings validate the central role of spin angular momentum for the CISS effect, paving the path toward the functionalization of hybrid molecule-metal interfaces via chirality.

In the recent years, chiral hybrid organic inorganic perovskites (HOIPs) have emerged as auspicious materials for optoelectronics, spintronics, photodetection, energy harvesting and more, allowing for the absorption and subsequent emission of polarized light with an enhanced tunability over the electromagnetic spectrum [1, 2]. In this growing field, a plethora of 2D and quasi-2D materials have been reported, as well as few 1D and 0D ones, demonstrating the attainment of promising chiroptoelectronic and spin-polarization features [3]. However, all these materials lack of metal-halide octahedra interconnection in the three dimensions, issue reasonably affecting their 3D conductivity thus limiting the practical applications, as the layers of organic cations behave as dielectrics [4]. Hence, development of such 3D-interconnected materials is a current research challenge, since the steric hindrance of many organic cations prevents the accordance with the Goldschmidt tolerance factor and only allows 3D chiral HOIPs to remain in the theoretical development stage.

In the present work, we report for the first time the attainment of a chiral AB₂X₆ perovskitoid, incorporating the chiral diamine R/S-3-aminoquinuclidine (R/S-3-AQ) and featuring 3D interconnection of the octahedra. Managing the reaction conditions, (R/S-3-AQ)Pb₂Br₆ as well as the 2D counterpart [(R/S-3-AQ)₂PbBr₄]·2Br were obtained, enabling us to investigate the role of dimensionality on the chiroptical response and conductivity. By UV-Vis absorption spectra we observed sharp absorption edges at ca. 410 and 390 nm for (R/S-3-AQ)Pb₂Br₆ and [(R/S-3-AQ)₂PbBr₄]·2Br, respectively, values resulting in a direct bandgap of ca. 3.0 and 3.2 eV. The CD signals indicated a substantially higher maximum for the 2D materials, in terms of mdeg, along with a g_CD of 4·10^-4 (R) and -3·10^-4 (S), almost on order of magnitude larger than the 3D perovskitoid, namely 6·10^-5 (R) and -9·10^-5 (S). This issue was expected and ascribed to the minor content of chiral molecules per formula unit of (R/S-3-AQ)Pb₂Br₆. Resistivity measurement as well as theoretical calculations are now ongoing to determine the conductivity features of (R/S-3-AQ)Pb₂Br₆ and [(R/S-3-AQ)₂PbBr₄]·2Br, thus the influence of material dimensionality on the charge transport. With this pioneering work we aim to disclose new parameters, i.e. dimensionality and consequently octahedra interconnection, on the conductivity of chiral perovskite-related materials, potentially enriching the application fields of this promising class of compounds.

Materials capable of efficient charge separation and the generation of manipulable radicals are essential for innovative applications in photovoltaics and photocatalysis, but also spintronics. Organic semiconductors are increasingly recognized as promising candidates for these technologies, primarily due to their high polarizability and low spin-orbit coupling. However, these advantages are often offset by the propensity for fast recombination of charge carriers, driven by their low dielectric constants and strong Coulombic interactions, which can severely limit device performance. To address these challenges, it is crucial to identify key parameters in material design that improve energy and electron transfer between pi-conjugated molecules or stabilize charge-separated (CS) states in donor-acceptor systems.

In our laboratory, we developed a versatile supramolecular approach using chromophores disubstituted with chiral oligopeptide-polymer chains to form helical, singular molecular stacks.¹ Notably, the photogeneration of charges persisting for days was observed in some of these strictly one-dimensional assemblies, including thiophene and dicyanoperylene bisimide derivatives.^2,3

In this work, we report on the investigation of the reasons for the stability of these charges in the dicyanoperylene bisimide-based nanowires. The study integrates experimental, computational, and theoretical approaches, offering a comprehensive insight into the photophysical properties of these nanowires. We demonstrate that spin-decorrelated CS states can be stabilized within covalent donor-acceptor entities through supramolecular assembly while nonetheless maintaining a degree of structural flexibility that enables critical intermolecular vibronic interactions supporting the longevity of the CS state.

We found that the anionic radical dicyanoperylene bisimides observed within the strongly excitonically coupled nanowires emerged from self-doping via a charge separation between the core and the substituents. This electron transfer reaction is achievable not only by photoexcitation but also thermally, leading to a permanently measurable population of radicals by steady-state spectroscopies, and the photomodulability of the radical concentration, thanks to kinetic trapping of excess population. The stability of some polarons stems at least partly from a significantly distinct geometrical equilibrium compared to the neutral stack, as well as a reorganization permitted by the balanced structural flexibility of the nanowires, in which chirality plays a determining role. Furthermore, the persistence of the photopumped population is facilitated by the presence of an energy barrier between the CS state and neutral ground state, especially due to the absence of hole and electron orbital overlap. Charge recombination, much like charge separation, necessitates electron transfer through intermediary vibronic states, akin to cascade processes in biological photosynthetic systems.

By combining favorable electronic and vibrational characteristics, the studied donor-acceptor system not only achieves effective charge separation but also extends the usable lifespan of the radicals generated. These findings thus pave the way to design systems that decouple charge separation efficiency from immediate radical reactivity, offering new potential for advanced energy and electronic devices.

The role of spin polarization and spin accumulation in chiral interfaces will be examined in the context of spin-dependent catalysis. A recent example [1] related to the influence of the CISS effect in water oxidation on mesoporous systems consisting of TiO2 and Au will be discussed. Specifically, the relevance of broken symmetry singlet states in gold nanoparticles coated with chemisorbed molecules, where depending on the nature of the atomic linker to the surface, a non-zero spin density in an otherwise magnetically inactive surface is created, will be considered as an important concept in understanding how spin polarization is originated in interfaces with no magnetic activity. In a more general context, a theoretical description of spin accumulation in chiral interfaces will be given in terms of a model where current in a molecular junction and spin density are calculated self-consistently, thereby providing a mechanism for this phenomenon that is of crucial importance in spintronics and spin-dependent chemistry