Introducing chiral organic spacers in low-dimensional metal-halide perovskites triggers chiroptical activity, making these materials of great interest for spintronic applications. To enable such applications, it is necessary to develop a deep understanding of the structure formation of chiral two-dimensional (2D) perovskites and its impact on their optical properties. While much attention has been dedicated to developing processing routes to control the properties of achiral 2D perovskites, the use of chiral cations introduces higher steric hindrance, thus significantly impacting structure formation. I will discuss how changing the processing conditions impacts the phase purity, microstructure, and chiroptical properties of chiral 2D perovskites. For example, in solution-processed chiral 2D perovskites, the choice of solvent or the use of additives enables control over the structure and microstructure of the deposited thin films. Alternatively, I will show that chiral 2D perovskites can be processed by thermal evaporation, opening new pathways to large-scale deposition and microstructuring. 

The chemical and structural flexibility of layered (2D) hybrid organic–inorganic metal-halide perovskites (HOIPs) has been proposed as an ideal platform for the synthesis of novel circularly polarized light emitters through the incorporation of chiral organic molecules, showing potential application in optoelectronics and spintronics.[1,2] Furthermore, the weak forces between the organic layers in the case of Ruddlesden-Popper 2D HOIPs, allow mechanical exfoliation of bulk crystals to obtain flakes[3] making possible their integration in nanodevices. Most studies to date have focused on bulk compounds, specifically on the unstable and toxic Pb-based HOIPs,[1,2] although Mn-based HOIPs apart from lower toxicity can show not only chiroptical but also magnetic properties[4]. In this work, we report the chiroptical properties of R- and S-β-methylphenethylammonium Mn chloride HOIPs, which exhibit antiferromagnetic order,[5] in both bulk and mechanically exfoliated flakes. In these compounds, we observe the red photoluminescence (PL) emission originating from the octahedrally coordinated Mn²⁺, with a PL redshift as they transition from bulk to flake form. Circular dichroism (CD) and circularly polarized luminescence (CPL) mirrored signals confirm the chirality transfer from the organic cations to the inorganic lattice in bulk materials, presenting g_lum values (0.01) among the highest reported for chiral hybrid Mn halides. This chirality is preserved in the exfoliated flakes, reaching degrees of circularly polarized PL (P) of up to 17% at 80K, which systematically decrease with increasing temperature as previously observed in 2D Pb-based HOIPs[6]. Additionally, angle-resolved PL measurements show that the PL emission and P are isotropic. Therefore, our results demonstrate that these 2D Mn-based HOIPs are highly valuable, as they can compete with their Pb analogs and offer additional functionalities for spin-optoelectronic applications, thanks to the magnetic behavior associated with Mn²⁺.[7]

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].

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 drive the generation of CPL spectra and the associated dissymmetry factors.

References

[1] Grancini, Nazeeruddin. Nat. Rev. Mater. 4, 4-22.

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

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

[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.

Over the last ten years, the role of hybrid metal halide perovskites has received significant attention as suitable materials for various electronic applications. Indeed, their outstanding optoelectronic properties such as high-power conversion efficiency, tunable bandgap, and high absorption coefficient, make them suited for several applications in different devices as photovoltaic cells, photodetectors, light emitting diodes, and sensors^[2]. Starting from the hybrid organic-inorganic perovskites (HOIPs), the introduction of a chiral molecule as organic cation leads to the breaking of the spatial inversion symmetry, allowing new possible designs based on the combination of polarity and chirality^[1,3].  In the scientific scene, this opened plenty of novel applications provided by outstanding chiroptical properties, such as circular dichroism, circular polarized emission, chiral induced spin selectivity and so on. To extend the actual knowledge of these chiral systems, it is important to investigate those parameters which have a major impact on the chirality transfer mechanism, with the final aim to unveil it. From a material chemistry point of view this involve an important work on materials’ structure, involving several modulations/substitutions on the latter. More specifically, in this contribution we will present the results of the role of the organic cation, showing the modulation of the optoelectronic properties engineering unconventionally chiral cation. Firstly, we decide to move away from the commercial chiral cation and to synthesize homologous series that can help unveil the role of the chemical nature of the cation on the chiroptical properties. We obtained a new phase (R-/S-AMOL)PbI₃ and the correspondence with the Sn^[4]. The work provides a comparison not only in terms of structural features and chiroptical properties but also in terms of computational modelling, which helps us to deeply understating the role of organic cation and the difference in terms of efficiency moving from a Pb-based perovskites to a Pb-free one. Final aim of this work is to unveil the impact of chemical degrees of freedom on the chirality transfer between the organic cation and the inorganic framework to provide tuning strategies for materials engineering.

Metal Halide Perovskites (MHPs) and their derivatives are the subject of intense research due to their remarkable optoelectronic properties and tunable bandgap [1]. Major applications include photovoltaic cells for three-dimensional perovskites, as well as photodetectors, photodiodes, and lasers for other perovskite-based materials. A significant modification that can be made to organic-inorganic metal halides is the introduction of chiral organic cations, leading to the emergence of chiroptical properties and the Rashba-Edelstein effect [2]. The latter is particularly interesting for spin-related phenomena such as chirality-induced spin selectivity (CISS).To date, most chiral metal halides contain lead, a toxic element subject to strict regulations. Therefore, the exploration of lead-free materials is crucial. In this study, we report the synthesis of bismuth (III)- and antimony (III)-containing chiral iodides, including R/S-1-(4-Chloro)-Phenylethylammonium (abbreviated as Cl-PEA) as the organic chiral cation. Single crystals with the stoichiometry Cl-PEA₄M₂I₁₀ (where M represents Bi or Sb) have been prepared for both enantiomers and the racemic compound, and their structures have been resolved via single-crystal XRD. Additionally, mixed Sb/Bi systems have been synthesized to investigate potential bandgap bowing, which has already been observed in analogous vacancy-ordered achiral perovskites [3], and already analysed via powder diffraction.The optical properties of the prepared samples have been analyzed using UV-Vis and CD spectroscopy. Finally, starting from the experimental data, computational modeling has been employed to optimize the crystal structures, determine the electronic band structure, and evaluate the presence and extent of Rashba splitting. The modeling has also been used to calculate the projected density of states (PDOS) and the total density of states (DOS) of our compounds. These calculations provide insights into the orbital contributions to the observed bandgap bowing and identify the contributing species.

During the  recent years, chiral hybrid organic-inorganic perovskites where the organic cations are the “source” of chirality, have received great attention from the physics and chemistry research community. Their functional properties enable the control of light, charge, and electron spins in the same materials. Here, we will discuss the intriguing “chirality transfer mechanism” in some newly synthesized ferromagnetic chiral hybrid inorganic perovskite along with their interplay with magnetism. Although the organic cations are chiral and polar molecules, their arrangement in the crystal structure results in a chiral non-polar space-group P212121. Moreover, we discuss a new chirality order parameter such as the electronic chirality measure (ECM) aiming at quantify the molecular cation chirality taking into account ionic and electronic degrees of freedom simultaneously. Also, the relation of ECM to physical properties of chiral hybrid perovskites will be discussed, so shedding light on the fundamental principles governing their behavior and paving the way for the development of innovative optoelectronic and spintronic devices. 

Chirality, the property of objects being mirror images but non-superimposable, is a fundamental characteristic found in diverse systems, from DNA helices to subatomic particles. When chiral systems interact with electron spin, they exhibit Chiral-Induced Spin Selectivity (CISS), enabling chiral molecules to act as spin filters. This remarkable phenomenon has transformative implications for spintronics, drug design, and understanding the origin of biological chirality. By employing advanced semiconductors like perovskites, we explore CISS under controlled conditions. These chiral perovskites not only enhance the CISS effect but also display unique optical properties, such as the ability to absorb and emit circularly polarized light, unlocking exciting opportunities for technologies like spin LEDs and chiral detectors.

Despite progress, the underlying mechanisms of CISS remain poorly understood, as static helical models fail to align with experimental data. To address this, my team is developing a unified theoretical framework that captures the intricate quantum interactions in real materials. By integrating Density Functional Theory (DFT), Tight Binding (TB), and Machine Learning, we aim to model electronic, vibrational, and optical properties within a cohesive transport model. Early findings reveal that spin-phonon coupling plays a vital role in spin selectivity, highlighting the importance of dynamic quantum effects.

With support from a recently awarded ERC Consolidator Grant, we are expanding this framework to include new quantum interactions and transport calculations from both semiclassical and fully quantum perspectives. Once complete, this framework will bridge the gap between theory and experiment, offering powerful tools to advance our understanding of chirality and propel next-generation chiral technologies.

Coupling chiral organic cations with the inorganic skeleton of perovskites is paving the way for new materials combining the second-order non-linear optical responses granted by the chiral molecules [1] and the modulable absorption and luminescence features settled by the perovskite or perovskite-derivative structures [2,3]. The heightened flexibility of design permitted by the vastity of available chemical constituents allows creating materials where the structural and functional parameters can be engineered, resulting in elevated circular dichroism, tunable photoluminescence, elevated spin selectivity, and more. Within this growing field, a deep understanding of how chemical composition and structural parameters impact on photophysical properties and chirality transfer mechanism is crucial, and parameters such as framework dimensionality, octahedral distortion and hydrogen bond network must be taken into account.

In this perspective, the current presentation will focus on novel hybrid organic inorganic perovskites (HOIPs) and their derivatives, attained through a rational tuning of the components to evaluate its impact on crystal structure and chiroptical properties. The effect of materials dimensionality on the chiral response will be discussed, including examples of 3D HOIPs derivatives which are not common due to the steric constrains of chiral cations. The metal centres impact on octahedra distortion, bandgap and chiroptical features will be examined, reporting results from our group with cations such as Sn^II and Ge^II in addition to the well-known Pb^II. The chiral cations modulation will also be presented, exploring molecules with mixed functionalities, i.e. simultaneously containing amino and hydroxyl groups, synthesized ad hoc to move away from the few commercially available ones. Finally, high-pressure studies unveiling the structural and optical response of chiral HOIPs upon external stimuli will be outlined.

It is generally accepted that spin-dependent electron transmission may appear in chiral systems, even without magnetic components, as long as significant spin–orbit coupling (SOC) is present in some of its elements [1]. However, this chirality-induced spin selectivity (CISS) can only manifest in experiments when system is taken out of equilibrium. Aided by group theoretical considerations and nonequilibrium DFT-based quantum transport calculations, here we show that, when spatial symmetries that forbid a finite spin polarization in equilibrium are broken, a net spin accumulation appears at finite bias in an arbitrary chiral two-terminal nanojunction. Furthermore, when a suitably magnetized detector is introduced into the system, the net spin accumulation, in turn, translates into a finite magneto-conductance [2]. These calculations have been possible thanks to new SOC implementation in our code ANT.Gaussian (https://github.com/juanjosepalacios/ANT.Gaussian). We also extend this analysis to chiral crystals where a similar phenomenology should be present in bulk. We do so thanks to a new code based on the computation of k-dependent transmission and polarization on top of a Hamiltonian obtained with CRYSTAL23.