ABSTRACT
Simultaneous enhancement of free excitons (FEs) emission and self-trapped excitons (STEs) emission remains greatly challenging because of the radiative pathway competition. Here, a significant fluorescence improvement, associated with the radiative recombination of both FEs and STEs is firstly achieved in an unconventional ACI-type hybrid perovskite, (ACA)(MA)PbI4 (ACA=acetamidinium) crystals with {PbI6} octahedron units, through hydrostatic pressure processing. Note that (ACA)(MA)PbI4 exhibits a 91.5-fold emission enhancement and considerable piezochromism from green to red in a mild pressure interval of 1 atm to 2.5 GPa. The substantial distortion of both individual halide octahedron and the Pb-I-Pb angles between two halide octahedra under high pressure indeed determines the pressure-tuning localized excitons behavior. Upon higher pressure, photocurrent enhancement is also observed, which is attributed to the promoted electronic connectivity in (ACA)(MA)PbI4. The anisotropic compaction reduces the distance between neighboring organic molecules and {PbI6} octahedra, leading to the enhancement of hydrogen bonding interactions. This work not only offers a deep understanding of the structure-optical relationships of ACI-type perovskites, but also presents insights into breaking the limits of luminescent efficiency by pressure-suppressed nonradiative recombination.
ABSTRACT
Achieving enhanced or blue-shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole-based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure-induced emission enhancement (PIEE) phenomenon with a 16-fold increase in fluorescence intensity from three-dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two-dimensional COFs with flexible structures exhibited rare blue-shifted emission, whereas the variants with rigid and conjugated structures showed common red-shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure-treated engineering and provides a new perspective on the design of piezochromic materials.
ABSTRACT
Developing hybrid metal halides with self-trapped exciton (STE) emission is a powerful and promising approach to achieve single-component phosphors for wide-color-gamut display and illumination. Nevertheless, it is difficult to generate STEs and broadband emission in the classical and widely used 3D systems, owing to the great structural connectivity of metal-halogen networks. Here, high pressure is implemented to achieve dual emission and dramatical emission enhancement in 3D metal halide of [Pb3 Br4 ][O2 C(CH2 )2 CO2 ]. The pressure-induced new emission is ascribed to the radiation recombination of STEs from the Pb2 Br2 O2 tetrahedra with the promoted distortion through the isostructural phase transition. Furthermore, the wide range of emission chromaticity can be regulated by controlling the distortion order of different polyhedral units upon compression. This work not only constructs the relationship between structure and optical behavior of [Pb3 Br4 ][O2 C(CH2 )2 CO2 ], but also provides new strategies for optimizing broadband emission toward potential applications in solid-state lighting.
ABSTRACT
Care should be taken when using amino acid ionic liquids (AAILs) for organic synthesis because of their multiple reactive groups. To expand the applicability of AAILs, we prepared a series of room-temperature ionic liquids derived from commercially available tert-butyloxycarbonyl-protected amino acids (Boc-AAILs). The resulting protected AAILs were used as the starting materials in dipeptide synthesis with commonly used coupling reagents. The distinctive coupling reagent N,N'-diethylene-N''-2-chloroethyl thiophosphoramide was found to enhance amide formation in the Boc-AAILs without addition of base, giving the dipeptides in satisfactory yields in 15 min.
ABSTRACT
Correction for 'Cryptand-imidazolium supported total synthesis of the lasso peptide BI-32169 and its d-enantiomer' by Ming Chen et al., Chem. Commun., 2019, 55, 3323-3326, DOI: .
ABSTRACT
Lasso peptides are attracting increasing attention due to their broad range of biological activities. The knot topology of lasso peptides, which contains an isopeptide bond-bridged macrocycle threaded by its C-terminal tail, has been proven to be an important structural feature for their bioactivities. The preparation of lasso peptides has been achieved by biosynthetic methods; nevertheless, a chemical synthesis of lasso peptides has not been described so far. Herein, a cryptand-imidazolium complex is designed as a multi-linker support and applied in the chemical synthesis of the lasso peptide BI-32169. Furthermore, the chiral switching of the support and the introduction of d-amino acids enable the synthesis of the d-enantiomer of BI-32169, which shows not only a strong glucagon receptor antagonist activity, but also a much higher enzymatic stability compared to the l-lasso peptide.