Synthesis of Layered Lead-Free Perovskite Nanocrystals with Precise Size and Shape Control and Their Photocatalytic Activity

Ni-Doped Perovskite for Photocatalytic Benzylic C-H Amination

Directly introducing aliphatic or aromatic amines into C(sp3)-H bonds remains a significant challenge in organic synthesis. One major difficulty is that C(sp3)-H activation is an oxidative process, whereas amines are generally more prone to oxidation than C-H bonds, making them difficult to use directly. Typically, protected amines are employed and then deprotected to realize amination, but this strategy limits the synthesis of tertiary amines, as protected secondary amines are often inactive in such reactions. Here, we present a mild photocatalytic method that overcomes these limitations by utilizing Ni-doped perovskite CsPbBr3 nanocrystals (NCs) for benzylic C-H amination directly using unprotected aliphatic or aromatic amines. Perovskite enables highly selective C-H activation, while doped Ni(II) readily captures benzylic radicals via oxidative addition. XPS studies successfully validate such an oxidative addition step with a Ni(II)/Ni(III) configuration. Our methodology forges aromatic and aliphatic, cyclic and acyclic, and secondary and tertiary amines and provides a powerful tool for the late-stage functionalization of bioactive compounds and drug derivatives.

Halide Perovskite Induces Halogen/Hydrogen Atom Transfer (XAT/HAT) for Allylic C-H Amination

Allylic C-H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C-H activation but furnishes reductive amines, inferring mild oxidants' inactivity for C-H oxidation but strong oxidants' detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen-vacancies of perovskite photocatalyst and exploits halogenated-solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C-H allyl amination with 19,376 turnovers. CsPbBr3 nanocrystals induce cooperative hydrogen-atom-transfer (HAT, C-H oxidation, and halogen-vacancy CsPbBr3-x formation) and halogen-atom-transfer (XAT, CsPbBr3-x-induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives.

Chiral Inorganic Polar BaTiO3/BaCO3 Nanohybrids with Spin Selection for Asymmetric Photocatalysis

Chirality-dependent photocatalysis is an emerging domain that leverages unique chiral light-matter interactions for enabling asymmetric catalysis driven by spin polarization induced by circularly polarized light selection. Herein, we synthesize chiral inorganic polar BaTiO3/BaCO3 nanohybrids for asymmetric photocatalysis via a hydrothermal method employing chiral glucose as a structural inducer. When excited by opposite circularly polarized light, the same material exhibits significant asymmetric catalysis, while enantiomers present an opposite polarization preference. More importantly, the preferred circularly polarized light undergoes reversal with reversal of the CD signal. Systematic experimental results demonstrate that more photogenerated carriers are generated in chiral semiconductors under suitable circularly polarized light irradiation, including more spin-polarized electrons, which inhibits the recombination of electron-hole pairs and promotes the activation of oxygen molecules into reactive oxygen species, thus inducing this asymmetric photocatalytic feature. This study provides valuable insights for the development of highly efficient polarization-sensitive chiral perovskite nanostructures as promising candidates for next-generation, multifunctional chiral device applications.

Lattice Engineering via Transition Metal Ions for Boosting Photoluminescence Quantum Yields of Lead-Free Layered Double Perovskite Nanocrystals

Lead-free layered double perovskite nanocrystals (NCs), i.e., Cs4M(II)M(III)2Cl12, have recently attracted increasing attention for potential optoelectronic applications due to their low toxicity, direct bandgap nature, and high structural stability. However, the low photoluminescence quantum yield (PLQY, <1%) or even no observed emissions at room temperature have severely blocked the further development of this type of lead-free halide perovskites. Herein, two new layered perovskites, Cs4CoIn2Cl12 (CCoI) and Cs4ZnIn2Cl12 (CZnI), are successfully synthesized at the nanoscale based on previously reported Cs4CuIn2Cl12 (CCuI) NCs, by tuning the M(II) site with different transition metal ions for lattice tailoring. Benefiting from the formation of more self-trapped excitons (STEs) in the distorted lattices, CCoI and CZnI NCs exhibit significantly strengthened STE emissions toward white light compared to the case of almost non-emissive CCuI NCs, by achieving PLQYs of 4.3% and 11.4% respectively. The theoretical and experimental results hint that CCoI and CZnI NCs possess much lower lattice deformation energies than that of reference CCuI NCs, which are favorable for the recombination of as-formed STEs in a radiative way. This work proposes an effective strategy of lattice engineering to boost the photoluminescent properties of lead-free layered double perovskites for their future warm white light-emitting applications.

Ultrasmall CsPbBr3 Nanocrystals as a Recyclable Heterogeneous Photocatalyst in 100% E- and Anti-Markovnikov Sulfinylsulfonation of Terminal Alkynes

The precise synthesis of ultrasmall, monodisperse CsPbBr3 nanocrystals is crucial due to their enhanced photophysical properties resulting from strong quantum confinement effects. Traditional methods struggle with size control, complicating synthesis. Although CsPbBr3 nanocrystals find applications in LEDs and photovoltaics, their use in photocatalysis for organic reactions remains limited. Our study introduces ultrasmall TBIA-CsPbBr3 nanocrystals (∼5.6 nm), synthesized via a three-precursor hot injection method using tribromoisocyanuric acid (TBIA) as a bromine precursor for the first time. These nanocrystals exhibit a near-unity photoluminescence quantum yield (PLQY) of 0.99 and an elevated oxidation potential of +1.80 V. We demonstrate their efficacy as recyclable heterogeneous photocatalysts in a one-pot, 100% E-selective, anti-Markovnikov sulfinylsulfonation of terminal alkynes under visible light, achieving a high product conversion rate (PCR) of 62,500 μmol g-1 h-1 and recyclability for up to five cycles. Density functional theory (DFT) calculations support the exclusive formation of the E-isomer. TBIA-CsPbBr3 outperforms other CsPbBr3 perovskites in photocatalysis, with superior efficiency attributed to their extended excited-state lifetime and higher surface area, which accelerates the organic transformation process.

Lanthanide Doping into All-Inorganic Heterometallic Halide Layered Double Perovskite Nanocrystals for Multimodal Visible and Near-Infrared Emission

The introduction of lanthanide ions (Ln3+) into all-inorganic lead-free halide perovskites has captured significant attention in optoelectronic applications. However, doping Ln3+ ions into heterometallic halide layered double perovskite (LDP) nanocrystals (NCs) and their associated doping mechanisms remain unexplored. Herein, we report the first colloidal synthesis of Ln3+ (Yb3+, Er3+)-doped LDP NCs utilizing a modified hot-injection method. The resulting NCs exhibit efficient near-infrared (NIR) photoluminescence in both NIR-I and NIR-II regions, achieved through energy transfer down-conversion mechanisms. Density functional theory calculations reveal that Ln3+ dopants preferentially occupy the Sb3+ cation positions, resulting in a disruption of local site symmetry of the LDP lattices. By leveraging sensitizations of intermediate energy levels, we delved into a series of Ln3+-doped Cs4M(II)Sb2Cl12 (M(II): Cd2+ or Mn2+) LDP NCs via co-doping strategies. Remarkably, we observe a brightening effect of the predark states of Er3+ dopant in the Er3+-doped Cs4M(II)Sb2Cl12 LDP NCs owing to the Mn component acting as an intermediate energy bridge. This study not only advances our understanding of energy transfer mechanisms in doped NCs but also propels all-inorganic LDP NCs for a wider range of optoelectronic applications.

Copper Modulated Lead-Free Cs4 MnSb2 Cl12 Double Perovskite Microcrystals for Photocatalytic Reduction of CO2

In order to deal with the global energy crisis and environmental problems, reducing carbon dioxide through artificial photosynthesis has become a hot topic. Lead halide perovskite is attracted people's attention because of its excellent photoelectric properties, but the toxicity and long-term instability prompt people to search for new photocatalysts. Herein, a series of <111> inorganic double perovskites Cs4 Mn1-x Cux Sb2 Cl12 microcrystals (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) are synthesized and characterized. Among them, Cs4 Mn0.7 Cu0.3 Sb2 Cl12 microcrystals have the best photocatalytic performance, and the yields of CO and CH4 are 503.86 and 68.35 µmol g-1 , respectively, after 3 h irradiation, which are the highest among pure phase perovskites reported so far. In addition, in situ Fourier transform infrared (FT-IR) spectroscopy and electron spin resonance (ESR) spectroscopy are used to explore the mechanism of the photocatalytic reaction. The results highlight the potential of this class of materials for photocatalytic reduction reactions.

Photocatalysis Based on Metal Halide Perovskites for Organic Chemical Transformations

Heterogeneous photocatalysts incorporating metal halide perovskites (MHPs) have garnered significant attention due to their remarkable attributes: strong visible-light absorption, tuneable band energy levels, rapid charge transfer, and defect tolerance. Additionally, the promising optical and electronic properties of MHP nanocrystals can be harnessed for photocatalytic applications through controlled crystal structure engineering, involving composition tuning via metal ion and halide ion variations, dimensional tuning, and surface chemistry modifications. Combination of perovskites with other materials can improve the photoinduced charge separation and charge transfer, building heterostructures with different band alignments, such as type-II, Z-scheme, and Schottky heterojunctions, which can fine-tune redox potentials of the perovskite for photocatalytic organic reactions. This review delves into the activation of organic molecules through charge and energy transfer mechanisms. The review further investigates the impact of crystal engineering on photocatalytic activity, spanning a diverse array of organic transformations, such as C-X bond formation (X = C, N, and O), [2 + 2] and [4 + 2] cycloadditions, substrate isomerization, and asymmetric catalysis. This study provides insights to propel the advancement of metal halide perovskite-based photocatalysts, thereby fostering innovation in organic chemical transformations.

Rational Atom Substitution to Obtain Efficient, Lead-Free Photocatalytic Perovskites Assisted by Machine Learning and DFT Calculations

Inorganic lead-free halide perovskites, devoid of toxic or rare elements, have garnered considerable attention as photocatalysts for pollution control, CO2 reduction and hydrogen production. In the extensive perovskite design space, factors like substitution or doping level profoundly impact their performance. To address this complexity, a synergistic combination of machine learning models and theoretical calculations were used to efficiently screen substitution elements that enhanced the photoactivity of substituted Cs2 AgBiBr6 perovskites. Machine learning models determined the importance of d10 orbitals, highlighting how substituent electron configuration affects electronic structure of Cs2 AgBiBr6 . Conspicuously, d10 -configured Zn2+ boosted the photoactivity of Cs2 AgBiBr6 . Experimental verification validated these model results, revealing a 13-fold increase in photocatalytic toluene conversion compared to the unsubstituted counterpart. This enhancement resulted from the small charge carrier effective mass, as well as the creation of shallow trap states, shifting the conduction band minimum, introducing electron-deficient Br, and altering the distance between the B-site cations d band centre and the halide anions p band centre, a parameter tuneable through d10 configuration substituents. This study exemplifies the application of computational modelling in photocatalyst design and elucidating structure-property relationships. It underscores the potential of synergistic integration of calculations, modelling, and experimental analysis across various applications.