Takunori Harada

A solid-state dedicated circular dichroism spectrophotometer: Development and application

A solid-state dedicated circular dichroism (CD) spectrophotometer (J-800KCM) was designed and constructed. As a CD spectrophotometer is a polarization–modulation instrument, CD spectra are necessarily accompanied by artifacts due to macroscopic anisotropies such as linear birefringence (LB) and linear dichroism (LD) which are unique to the solid state. A photomultiplier with the least polarization characteristics and a photoelastic modulator (PEM) with the least residual static birefringence were selected for the new instrument, which was based on the electrical and optical systems of a commercially available spectrophotometer. A phased-locked loop circuit was introduced to a PEM driver, and a sample rotation holder, a stage controller, and an analyzer were installed. We have designed and built a special solid-state sample holder to enable the cancellation of artifact CD, and a lens unit for smaller samples. A set of procedures for obtaining true CD has been devised based on the Mueller matrix method, and...

Facile Synthetic Route to Highly Luminescent Sila[7]helicene

A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large g value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules.

On the Mechano‐Chiral Effect of Vortical Flows on the Dichroic Spectra of 5‐Phenyl‐10,15,20‐tris(4‐sulfonatophenyl)porphyrin J‐Aggregates

Phase-modulated ellipsometry of the J-aggregates of the title porphyrin shows that the material gives a true CD signal. This confirms that there is a real chiral transfer by mechanical forces, mediated by shear gradient flows, from the macroscopic to the electronic transition level. Dislocations in the structure of the aggregate could justify the formation of chirality at the level of the electronic transitions once the mesophases can be sculptured by hydrodynamic gradient flows.

Control of the Solid‐State Chiral Optical Properties of a Supramolecular Organic Fluorophore Containing 4‐(2‐Arylethynyl)‐Benzoic Acid

The solid-state chiral optical properties of a 4-(2-arylethynyl)-benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4-(2-arylethynyl)-benzoic acid component molecule rather than the chirality of the amine component molecule.

Phase-Sensitive Supramolecular Chirogenesis in Bisporphyrin Systems**

To date, the field of supramolecular chirality has attracted much attention in the scientific community, in the context of its direct connection with various natural systems and many practical applications in the areas of catalysis,[1] nonlinear optics,[2] polymer and materials science,[3] molecular recognition,[4] molecular devices,[5] and absolute configuration determination.[6] As noncovalent interactions are the key elements of supramolecular chemistry, there are various external and internal factors controlling chirality induction in these systems. Among these influences, the phase transition, or aggregation state, takes on particular significance in the light of the wide prospective applications of optically active systems in the solid state.[7] However, this important factor has not yet been well investigated and rationalized. Here, by applying supramolecular chemistry, solid-state optical spectroscopy, and exciton chirality principles, we describe a novel and intriguing phenomenon of phasetransition controlled chirality induction in a supramolecular system, which consists of an achiral host and a chiral guest.[8] Ethane-bridged bis(zinc octaethylporphyrin),[9] which is in a syn conformation in nonpolar solvents (see syn ZnD in Figure 1), was chosen as an achiral host molecule. This

Crystal chirality of the non-chiral inorganic salt, α-Ni(H2O)6.SO4

Abstract Solid phase circular birefringence (CB = optical rotatory dispersion) and circular dichroism (CD) spectra of α-Ni(H2O)6·SO4, which exhibits optical activity only in the crystalline state, were studied in the 250–600 nm region. A method was devised to remove signals which arise from linear birefringence (LB) and linear dichroism (LD) and give pure CB spectra by using a specially constructed universal chiroptical spectrophotometer. Even in the cases where LB is substantial, the pure CB and CD spectra thus obtained were shown to satisfy the Kramers–Kronig relationship in the 3 A 2 g → 3 T 1 g ( P ) Ni d–d transition region, as do chiral compounds in isotropic medium.

Control of circularly polarized luminescence (CPL) properties by supramolecular complexation

The sign of circularly polarized luminescence (CPL) of a chiral 21-helical columnar organic fluorophore was successfully controlled in the solid-state by changing an achiral fluorescence component molecule, and not by using a chiral component molecule with opposite chirality.

CD measurements of β-amyloid (1-40) and (1-42) in the condensed phase.

Circular dichroism (CD) spectroscopy of proteins/peptides in thin films can provide valuable information on the structures in the aggregated states; however, it is difficult to estimate the secondary structure content quantitatively due to artifact signals arising from macroscopic anisotropies which is unique to the solid phase. Using a Universal Chiroptical Spectrophotometer (UCS-1) together with the measurement and analytical procedures we have developed, we could obtain artifact-free CD spectra of cast and Langmuir-Blodgett (L-B) films of synthetic peptides, Aβ (1-40) and (1-42) which are related to Alzheimers disease. The work gave insights into the mechanisms for structural transformation and amyloid-like aggregation.

Vertical-type chiroptical spectrophotometer (I): Instrumentation and application to diffuse reflectance circular dichroism measurement

We have designed and built a novel universal chiroptical spectrophotometer (UCS-2: J-800KCMF), which can carry out in situ chirality measurement of solid samples without any pretreatment, in the UV-vis region and with high relative efficiency. The instrument was designed to carry out transmittance and diffuse reflectance (DR) circular dichroism (CD) measurements simultaneously, thus housing two photomultipliers. It has a unique feature that light impinges on samples vertically so that loose powders can be measured by placing them on a flat sample holder in an integrating sphere. As is our first universal chiroptical spectrophotometer, UCS-1, two lock-in amplifiers are installed to remove artifact signals arising from macroscopic anisotropies which are unique to solid samples. High performance was achieved by theoretically analyzing and experimentally proven the effect of the photoelastic modulator position on the CD base line shifts, and by selecting high-quality optical and electric components. Measurement of microcrystallines of both enantiomers of ammonium camphorsulfonate by the DRCD mode gave reasonable results.

Multiple molecular response columnar host system composed of rac-2-amino-1,2-diphenylethanol and 1-fluorenecarboxylic acid

By using racemic (rac)-2-amino-1,2-diphenylethanol and achiral fluorescent 1-fluorenecarboxylic acid, a two-component columnar host system with multiple molecular response (guest-dependent spontaneous resolution and fluorescence) properties in the solid state was created.