Solid-state ECD Research Articles

Cover Feature: Electronic Circular Dichroism Imaging (ECD i ) Casts a New Light on the Origin of Solid‐State Chiroptical Properties (Chem. Eur. J. 4/2022)

Thanks to the concept of synchrotron radiation ECD imaging (SR-ECDi) applied to the active pharmaceutical ingredient Finasteride, we obtained an exclusive insight into the critical role played by the anisotropy of local domains in solid-state ECD spectra. Our findings open a new way to interpret solid-state chiroptical measurements and will broaden their application to probing and mapping solid chiral materials. More information can be found in the Research Article by M. Górecki, L. Di Bari, et al. (DOI: 10.1002/chem.202103632).

Electronic Circular Dichroism Imaging (ECDi) Casts a New Light on the Origin of Solid-State Chiroptical Properties.

Solid-state ECD (ss-ECD) spectra of a model microcrystalline solid, finasteride, dispersed into a KCl pellet were recorded by using the synchrotron radiation source at the Diamond B23 beamline. Scanning a surface of 36 mm2 with a step of 0.5 mm, we measured a set of ECD imaging (ECDi) spectra very different from each other and from the ss-ECD recorded with a bench-top instrument (1 cm2 area). This is due to the anisotropic part of the ECD (ACD), which averages to zero in solution or on a large number of randomly oriented crystallites, but can otherwise be extremely large. Two-way singular value decomposition (SVD) analysis, through experimental and simulated TDDFT spectra, disclosed that the measured and theoretical principal components are in line with each other. This finding demonstrates that the observed isotropic ss-ECD spectrum is governed by the anisotropy of locally oriented crystals. It also introduces a new quality for ss-ECD measurements and opens a new future for probing and mapping chiral materials in the solid state such as active pharmaceutical ingredients (APIs).

Synthesis and structure analysis of ferrocene-containing pseudopeptides.

Ferrocene with its aromaticity and facile redox properties is an attractive moiety to be incorporated into functional moieties. Medicinal applications of ferrocene are well known and ferrocene itself shows cytotoxic and antianemic properties. In this article, we will describe the synthesis and the structure analysis of two pseudopeptides containing a ferrocene moiety as N-terminal group. After purification, Fc-l-Phe-d-Oxd-OBn [l-Phel-phenylalanine; d-Oxd(4R,5S)-4-Methyl-5-carboxy-oxazolidin-2-one] appears as bright brown solid that spontaneously forms brown needles. The X-ray diffraction of the crystals shows the presence of strong π interactions between the ferrocenyl moiety and the phenyl rings, while no NH•••OC hydrogen bonds are formed. This result is confirmed by FT-IR and 1 H NMR analysis. In contrast, both FT-IR and 1 H NMR analysis suggest that Fc-(l-Phe-d-Oxd)2 -OBn forms a turn conformation stabilized by intramolecular NH•••OC hydrogen bonds in solution. Chiroptical spectroscopies (ECD and VCD) substantially confirmed the absence of a well-defined folded structure. The presence of the Fc moiety is responsible for specific ECD signals, one of which displayed pronounced temperature dependence and is directly related with the helicity assumed by the Fc core. Solid-state ECD spectra were recorded and rationalized on the basis of the X-ray geometry and quantum-mechanical calculations.

Incorporation of plastic crystal and transparent UV-cured polymeric electrolyte in a complementary electrochromic device

The plastic crystal, namely succinonitrile (SN), has been incorporated with a UV-cured ethoxylated trimethylolpropane triacrylate (ETPTA) polymer to form a transparent, self-standing polymeric crystal composite electrolyte (PCCE). The PCCE, containing cross-linked polymer ETPTA and SN with 0.1M tetrabutylammonium tetrafluoroborate (TBABF4), is proposed as the solid polymer electrolyte for electrochromic application. The weight ratio of ETPTA/SN is controlled at 85/15. Under a UV-exposure time of 30s, the PCCE turns into a transparent solid with an excellent interfacial adhesion between two electrochromic thin films. The chosen anodic and cathodic coloring materials are polyaniline-carbon nanotubes (PANIs-CNT) and poly(butyl viologen) (PBV) thin films, respectively.The PANI/PCCE/PBV solid-state ECD exhibits two stages of color change, with the first stage redox reaction occuring between −1.0 and 0.5V (PANI-CNTs vs. PBV) and the second stage occurs between 0.5 and 1.5V. At 550nm, the solid-state ECD shows a transmittance change of 39% and a coloration efficiency of 151.3cm2/C, respectively. The transmittance of the ECD at 550nm can be changed reversibly from 54% (bleached) to 15% (darkened) with the applied potentials of −2.0 and 0.75V, respectively. Electrochemical and electrochromic properties of the ECD are studied using cyclic voltammetry (CV) and UV–vis-NIR spectroscopy.

Circular Dichroism Spectroscopy Study of Crystalline‐to‐Amorphous Transformation in Chiral Platinum(II) Complexes

Two couples of enantiomeric platinum(II) complexes: Pt(L1a )Cl (1a), Pt(L1b )Cl (1b) and Pt(L1a )(C ≡ C - Ph) (2a), Pt(L1b )(C ≡ C - Ph) (2b) (L1a = (+)-1,3-di-(2-(4,5-pinene)pyridyl)benzene, L1b = (-)-1,3-di-(2-(4,5-pinene)pyridyl)benzene) were synthesized and characterized. Their absolute configurations were determined by single crystal X-ray diffraction and further verified by circular dichroism (CD) spectra (including electronic circular dichroism [ECD] and vibrational circular dichroism [VCD]). These complexes show interesting mechanoluminescence and/or vapoluminescence due to crystalline-to-amorphous transformation. The crystalline solids, grinding-induced amorphous powders, and vapor-induced amorphous powders of complexes 2a and 2b were comparatively investigated by solid-state ECD and VCD spectra. The transformation from crystalline solids to amorphous powders was accompanied by significant variances of the spectral feature in both ECD and VCD spectra.

Trend of large scale and solid state ECD.

In this article, the fundamental concept and structure of reflective and transmissive ECD's are reviewed. Various types of ECD's such as large-scale or solid-state ECD's are describedin terms of their performances. In the discussion it is concluded that the response of large-scale or solid-state ECD's is reduced primarily due to the presence of resistivity of TCO. Finally some possibility of large-scale and solid-state ECD's is discussed with a prospective materials survey.

Solid-state electrochromic device consisting of amorphous WO3 and Cr2O3

The electrochromic (EC) characteristics were investigated on a solid-state EC device In2O3/a-WO3//Cr2O3/Au which was prepared by vacuum deposition. Besides the color change caused by passage of current in the WO3 layer, the color of the Cr2O3 layer was also changed as a result of electrochemical reaction at the interface. In the open-circuit condition after the coloration, rapid spontaneous discoloration was found due to bimolecular recombination of the colored species in both layers at the interface. The existence of adsorbed water molecules in the respective layers is essential for the solid-state ECD. The ECD in this study was scarcely affected by the ambient condition and was able to operate in the high vacuum (e.g., 10—6 Torr) since the Cr2O3 layer adsorbed water tightly. Positive polarization of the Cr2O3 layer in an electrolyte solution (Na2SO4 aqueous solution) caused change in the color as a result of electrochemical reaction, whereas the coloration of a-WO3 was taken place by negative polarization of the a-WO3. We have confirmed that this ECD could be operated without any conspicuous deterioration after the reversible switching cycles more than 5×106 times.