Design of an Ad Hoc Bifunctional Chiral Ligand for the Preparation of Low-Dimensional Perovskites

We report here the preparation of a novel bifunctional chiral ligand (R) and (S)-1-ammino-2-butanol (AMOL) containing both an amine and hydroxyl group and its use in the preparation of chiral lead iodide perovskites. The incorporation of this bifunctional ligand leads to the synthesis of the [(R-/S-)-AMOL]2PbI3·I samples characterized by an uncommon structural motif composed by 1D double chains running along the crystallographic c-axis built up by face-sharing [PbI6]4- octahedra. Chiroptical properties determination shows and effective chirality transfer from the novel chiral ligands to the inorganic framework with a relevant optical response. The expansion of the library of actually known chiral ligands will not only help the design of novel chiral perovskites but will also provide useful insight into the definition of solid structure-property correlations

Synthesis and Characterization of Cu-containing Chiral Metal Halides and Role of Halogenation of the Organic Ligand

We report herein novel chiral copper metal chlorides, namely (R/S-ClMBA)2CuCl4 (ClMBA = 4-(chloromethyl)benzylammonium), together with the corresponding racemic compound. The two chiral samples are composed of isolated CuCl4 tetrahedra and crystallize in the non-centrosymmetric C2 space group and present a significant absorption in the visible region of the spectrum with band gap around 2.50 eV. The racemic compound, on the other hand, gives origin to a different structural topology characterized by the presence of a quite unusual five coordination for Cu(II), with Cu2Cl6- dimers forming infinite chains along the b axis and presents, in addition, a strong reduction of band gap (around 1.76 eV). The two chiral samples display a circular dichroism response with anisotropy factors values around 0.02. The actual novel samples are investigated in comparison to the MBA-based (MBA=methylbenzylammonium) system in order to unveil the role of benzene ring halogenation on the structural and chiroptical properties indicating that the presence of chlorine leads to a doubling of the anisotropy factor

(R/S-ClMBA)3GeI5: A Novel Low-Dimensional Ge-Containing Chiral Perovskite

We report here the first chiral perovskite containing germanium, namely (R/S-ClMBA)3GeI5. Single crystal x-ray diffraction shows the for-mation of a crystal structure composed of GeI6 octahedra arranged in linear zig-zag chains running along the b-axis, providing a one-dimensional (1D) system with a novel structural motif. The presence of Ge leads to the highest values of octahedral distortion parameters among chiral perovskites. Chiroptical properties determination by circular dichroism confirms the effective chirality transfer from the ligands to the in-organic framework with asymmetry factors of the order 10–3, with maximum absorbance around 420 nm. The demonstration of the successful preparation of Ge-based chiral perovskites with clear chiroptical properties may open the way for the future design of novel and optimized materials

Halide alloying and role of central atom on the structural and optical properties of decylammonium germanium 2D perovskites

We report here a novel series of halide alloyed Ge-containing 2D perovskites including decylammonium as organic spacer, namely DA2Ge(Br1−xIx)4. This system forms a continuous solid solution on the halide site with a modulation of the bandgap from 2.74 to 2.17 eV with a rapid decrease up to x = 0.5 followed by a plateau. Iodide-rich compositions show enhanced broad room temperature (RT) photoluminescence (PL) that narrows at low temperature with maximum quantum yields for mixed compositions. The replacement of Ge with Pb and Sn in DA2GeBr4 and DA2GeI4 provides a tuning of the bandgap in the whole visible spectrum with a marked blue-shift when lead is present and, opposite, a red-shift for Sn replacement. The RT PL progressively broadens moving from Pb to Sn and to Ge covering an emission range from 400 to 800 nm. Finally, the air stability of lead-free 2D perovskites of this work has been determined indicating its improvement by increasing the hardness of the halide

Halide Alloying and Role of Central Atom on the Structural and Optical Properties of Decylammonium Germanium 2D Perovskites

We report here a novel series of halide alloyed Ge-containing 2D perovskites including decylammonium as organic spacer, namely DA2Ge(Br1-xIx)4. This system forms a continuous solid solution on the halide site with a modulation of the band gap from 2.74 to 2.17 eV with a rapid decrease up to x=0.5 followed by a plateau. Iodide-rich compositions show enhanced broad RT photoluminescence (PL) which narrows at low temperature with maximum quantum yields for mixed compositions. The replacement of Ge with Pb and Sn in DA2GeBr4 and DA2GeI4 provides a tuning of the band gap in the whole visible spectrum with a marked blue-shift when lead is present and, opposite, a red-shift for Sn replacement. The RT PL progressively broadens moving from Pb to Sn and to Ge covering an emission range from 400 to 800 nm. Finally, the air stability of lead-free 2D perovskites of this work has been determined indicating its improvement by increasing the hardness of the halide

Ligand-Induced Chirality in Novel 2D Tin Iodide Perovskite Cl-MBA2SnI4

Chiral perovskites possess a huge applicative potential in several areas of optoelectronics and spintronics. The development of novel lead-free perovskites with tunable properties is a key topic of current research. Herein, we report a novel lead-free chiral perovskite, namely (R/S-)ClMBA2SnI4 and the corresponding racemic system. The reported ClMBA2SnI4 samples exhibit a low band gap (2.12 eV) together with broad emission extending in the red region of the spectrum (1.7 eV). Chirality transfer from the organic ligand induces chiroptical activity in the 465-530 nm range. Density function theory calculations show a Rashba type band splitting for the chiral samples and no band splitting for the racemic isomer. Self-trapped exciton formation is origin of the large Stokes shift in the emission. Careful correlation with analogous lead and lead-free chiral perovskites confirms the role of the symmetry-breaking distortions in the inorganic layers associated with the ligands as the source of the observed chiroptical properties providing also preliminary structure-property correlation in 2D chiral perovskites

Air- and water-stable and photocatalytically active germanium-based 2D perovskites by organic spacer engineering

There is increasing interest in the role of metal halide perovskites for heterogeneous catalysis. Here, we report a Ge-based 2D perovskite material that shows intrinsic water stability realized through organic cation engineering. Incorporating 4-phenylbenzilammonium (PhBz) we demonstrate, by means of extended experimental and computational results, that PhBz2GeBr4 and PhBz2GeI4 can achieve relevant air and water stability. The creation of composites embedding graphitic carbon nitride (g-C3N4) allows a proof of concept for light-induced hydrogen evolution in an aqueous environment by 2D Ge-based perovskites thanks to the effective charge transfer at the heterojunction between the two semiconductors

Erratum to: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition) (Autophagy, 12, 1, 1-222, 10.1080/15548627.2015.1100356

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