Self-Assembly of Thienopyrrole-Fused Thiadiazoles Containing an Amide Linker: Control of Supramolecular Polymerization Mechanism and Chiroptical Properties by Trialkoxy Side Chains.

Three thienopyrrole-fused thiadiazole (TPT) fluorescent dyes featuring a common amide linker and different alkoxy substituents on peripheral trialkoxybenzene moieties were synthesized, and their self-assembly behavior in solution was investigated. The obtained results revealed a substantial steric effect of the alkoxy substituents on the supramolecular polymerization mechanism, which results from a combination of π-stacking and hydrogen (H)-bonding interactions. Detailed spectroscopic measurements revealed that with increasing steric demand of the substituents, the supramolecular polymerization processes in pure methylcyclohexane (MCH) or a mixture of MCH and toluene become temperature-sensitive and enthalpically favorable, resulting in a change from the isodesmic assembly mechanism to the cooperative mechanism. Theoretical calculations suggested that in TPTs with bulky substituents, steric hindrance causes the H-bonding array of the amide moieties to be aligned along the stacking axis of the π-systems; thus, the H-bonding interactions are strengthened compared to those in TPTs with less bulky substituents, compensating for the weakened π-stacking interactions. A chiral TPT derivative with (S) stereogenic centers was found to form homochiral helical supramolecular assemblies that generate discernible circularly polarized luminescence. Achiral TPTs also generate helical assemblies to which preferential helicity can be imparted through the external chiral bias of the solvents (R)- and (S)-limonene.

Chiroptically Active Host-Guest Composites Using a Terpene-Based Micellar Capsule.

For the design of a new chiroptically active host-guest system, a bent amphiphilic compound was synthesized using cyclic monoterpenes as key biorelated chiral frameworks. In water, the bent amphiphiles form a terpene-based micellar capsule with a core diameter of ∼2 nm in a spontaneous and quantitative fashion. The resultant chiral capsule shows wide-ranging uptake abilities toward achiral fluorescent dyes in water. Notably, relatively strong CD bands are generated from the resultant host-guest composites, e.g., possessing AIE-active tetraphenylethene and sterically demanding BODIPY dyes, through efficient host-to-guest chirality transfer. The composites also display CPL, with moderate to high emission asymmetry factors (|glum| = up to 3.3 × 10-3).

Configuration of two cysteine residues in a ring within a stapled Bim peptide affects the secondary structure and apoptotic activity.

Many reports have shown that stabilization of secondary structure by stapling functional peptides enhances the intracellular bioactivity. However, no report has discussed the correlation between stabilization and biological activity based on the configuration of amino acid residues used as anchors for stapling. To clarify this, we investigated the helix content and apoptotic efficiency of an apoptosis-inducing peptide, Bim, and four stapled Bim peptides containing stapling-related Cys residues introduced with different configurations within the sequence. The results demonstrated that the configuration of Cys residues in stapled Bim peptides affected the secondary structure and intracellular activity of the peptides, and furthermore, there was a correlation between these latter two variables.

Circularly polarised luminescence from intramolecular excimer emission of bis-1,8-naphthalimide derivatives.

Chiral excimers exhibit unique photophysical behaviour. However, further molecular design is required along with systematic studies on the effect of spacer groups and solvent polarity. In this study, we prepared four circularly polarised luminescence (CPL)-active molecules that exhibit intramolecular excimer emission. Bis-1,8-naphthalimide (bNI) derivatives D-LybNI, L-LybNI, D-LyMebNI, and L-LyMebNI were prepared with chiral backbones and alkyl linkages between the NI rings with chain lengths of five carbon atoms, suitable for excimer fluorescence. The fluorescence properties were investigated experimentally and theoretically using density functional theory. The molecules exhibited intramolecular excimer fluorescence in polar organic solvents. Mirror-image circular dichroism and CPL spectra were obtained for the D and L forms. D- and L-LyMebNI exhibited relatively large luminescence dissymmetry factors (|glum|) in acetonitrile of 1.9 × 10-3 and 1.6 × 10-3, respectively. Thus, this study demonstrates chiral bNI derivatives with simple synthesis procedures that emit intramolecular excimer fluorescence and have effective CPL properties. These molecules are promising for developing organic molecular systems with bright, highly polarised emission.

Dual-Stimuli-Responsive Turn-On Luminescence of Chiral Bisimidazolyl BINOL Dimethyl Ether Crystals.

Stimuli-responsive organic luminescent crystals have attracted significant attention in recent years for their potential in sensor and memory applications. While turn-on luminescence is superior in detection sensitivity compared with turn-off luminescence, the development of organic crystals that exhibit turn-on luminescence in response to multiple stimuli remains a significant challenge. Herein, the crystals of chiral bisimidazolyl 1,1'-bi-2-naphthol (BINOL) dimethyl ether have exhibited a dual-stimuli-responsive turn-on luminescence based on two distinct mechanisms. In the crystalline state, luminescence was substantially quenched by the intermolecular hydrogen bonds between the imidazole rings. Mechanical stimulation induced a transition to a blue-violet-emissive amorphous state. In contrast, thermal stimulation produced an orange luminescence, attributed to excited-state intramolecular proton transfer (ESIPT) luminescence from thermally demethylated products. Furthermore, the thermally induced state exhibited circularly polarized luminescence (CPL), marking a rare instance of stimuli-responsive turn-on CPL in a solid-state system. This study provides new insights into environmental and structural factors for solid-state luminescent properties and advances the design guidelines for multifunctional luminescent sensors.

Synthesis and Optical Properties of Binaphthyl Derivatives with Comprehensive Introduction of Phenylethynyl Groups.

In this study, compounds with phenylethynyl (PE) groups introduced at all of the possible positions of the methylene-bridged structure of the 1,1'-bi-2-naphthol backbone (3-PE to 8-PE) were synthesized. Compounds with four or six phenylethynyl groups (3,6-PE, 4,6-PE, 5,6-PE, 6,7-PE, and 3,4,6-PE) were also synthesized. The key reaction for the synthesis of these compounds was the Sonogashira reaction using halogen scaffolds. The new transformation methods include (1) selective bromination of the 5-position of the binaphthyl skeleton and (2) bromination of the 6-position and then iodination of the 4-position, followed by the Sonogashira reaction of iodine at the 4-position and lithiation and protonation of bromine at the 6-position. The optical properties of the compounds were evaluated. The extension of the π system greatly differed depending on the position of the phenylethynyl group. 4-PE, 4,6-PE, and 3,4,6-PE, in which the phenylethynyl groups were introduced in the extended direction of the naphthalene linkage axis, showed longer absorption and emission wavelengths and higher fluorescence quantum yields than the other compounds. In circularly polarized luminescence measurements, 7-PE showed a relatively large glum value, an interesting finding that reverses the sense.

Impact of helical elongation of symmetric oxa[n]helicenes on their structural, photophysical, and chiroptical characteristics.

The adjustment of the main helical scaffold in helicenes is a fundamental strategy for modulating their optical features, thereby enhancing their potential for diverse applications. This work explores the influence of helical elongation (n = 5-9) on the structural, photophysical, and chiroptical features of symmetric oxa[n]helicenes. Crystal structure analyses revealed structural variations with helical extension, impacting torsion angles, helical pitch, and packing arrangements. Through theoretical investigations using density functional theory (DFT) calculations, the impact of helical extension on aromaticity, planarity distortion, and heightened chiral stability were discussed. Photophysical features were studied through spectrophotometric analysis, with insights gained through time-dependent DFT (TD-DFT) calculations. Following optical resolution via chiral high-performance liquid chromatography (HPLC), the chiroptical properties of both enantiomers of oxa[7]helicene and oxa[9]helicene were investigated. A slight variation in the main helical scaffold of oxa[n]helicenes from [7] to [9] induced an approximately three-fold increase in dissymmetry factors with the biggest values of|glum| of oxa[9]helicene (2.2 × 10-3) compared to|glum|of oxa[7]helicene (0.8 × 10-3), findings discussed and supported by TD-DFT calculations.

Supramolecular Chirality Achieved by Assembly of Small π-Molecules of Octahydrobinaphtols with Axial Chirality.

5,5',6,6',7,7',8,8'-Octahydro-1,1'-bi-2-naphthol (hbNaph) is an axially chiral molecule consisting of a smaller π-electronic system than that for 1,1'-bi-2-naphthol (BINOL). The absorption and circular dichroism (CD) bands of hbNaph appear in a shorter wavelength region below 310 nm, compared to those of BINOL, and its fluorescence is in the invisible UV region. However, increasing the concentration of hbNaph in solution up to 0.1 M results in its absorption edge gradually extending to longer wavelength, with a shoulder around 330 nm, and finally increasing to about 450 nm. At the same time, blue fluorescence is clearly observed, as well as a new CD band with the sign of the Cotton signals reversed from those obtained for dilute solutions. These results suggest that, at high concentrations, hbNaph forms chiral aggregates, in which π-electrons are delocalized over multiple molecules. To further understand how molecular axial chirality is transformed to supramolecular chirality, we attempted to construct aggregate models by simulating CD spectra using a time-dependent density functional theory. The only reasonable model obtained was that involving the counterclockwise R-enantiomer forming a clockwise helix, while the clockwise S-enantiomer forms a counterclockwise helix. We conclude, however, that, for such helixes, the most plausible model is densely packed and forms when the dihedral angle between the two phenol rings of hbNaph is acute, at around 75°, which reproduces the aggregate-induced CD sign inversion.

Synthesis and Isolation of a Homochiral Nanohoop Composed of a Tröger's Base and Hexaparaphenylene.

Invited for the cover of this issue are Yusuke Yoshigoe, Hirotaka Shimada, and Shinichi Saito at the Tokyo University of Science, and Takuya Takaki and Yoshitane Imai at Kindai University. The image depicts a witch with a racemic pair of our nanohoops, TB[6]CPPs, chanting words shown in the font of a magical world. Read the full text of the article at 10.1002/chem.202304059.

Circularly polarized phosphorescence with a large dissymmetry factor from a helical platinum(II) complex.

A chiral platinum(II) complex with a helical Schiff-base [4]helicene ligand exhibits intense red circularly polarized phosphorescence (CPP) with a glum of 0.010 in the dilute solution state. The intense CPP was caused by a change in the electronic transition character based on the induction of the helical structure.

Construction of high-throughput magnetic circular dichroism measurement system and its application to research on magnetic and optical properties of phthalocyanine complexes.

Magnetic circular dichroism (MCD) spectroscopy is a powerful method for evaluating the electronic structure and magnetic and optical properties of molecules. In particular, MCD measurements have been performed on phthalocyanines and porphyrins with various central metal ions, axial ligands, and substituents to elucidate their properties. It is essential to develop a robust high-throughput technique to perform these measurements comprehensively and efficiently. However, MCD spectroscopy requires very high optical quality for each component of the instrument, and even slight cell distortions can impair the baseline flatness. Consequently, when versatility and data quality are important, an optical system designed for a microplate reader is not suitable for the MCD spectrometer. Therefore, in this study, we develop a new magnetic flow-through cell and combine it with an existing CD spectrometer and autosampler to construct a high-throughput system. The effectiveness and performance of this new system are then evaluated. In addition, based on the MCD and absorption spectra of various phthalocyanine complexes, the effects of substituents and solvents on their magnetic and optical properties and the causes of these effects are discussed. The results demonstrate that this system is effective for the evaluation of the physicochemical properties of various phthalocyanine complexes.

Synthesis and Isolation of a Homochiral Nanohoop Composed of a Tröger's Base and Hexaparaphenylene.

The synthesis of a new nanohoop containing a stereogenic Tröger's base skeleton tethered to a curved hexaparaphenylene ([6]CPP) is reported. The TB[6]CPP nanohoop possesses a stable C2 symmetrical structure, which promotes the allowed transition that gives rise to pale blue emission with a quantum yield of ~0.69, surpassing the value of the more symmetrical [8]CPP. Moreover, TB[6]CPP shows chiroptical properties including circular dichroism and circularly polarized luminescence with a moderate dissymmetry factor (|glum|) of ~2.1×10-3.

Circularly Polarized Luminescence from Schiff-base [4]Helicene Boron Complexes.

Boron complexes with Schiff-base [4]helicene ligands were synthesized. These complexes were characterized by NMR spectroscopy and their helical molecular structures were unequivocally established by X-ray diffraction (XRD) analysis. The helical boron complexes exhibited efficient photoluminescence under UV irradiation, and the circularly polarized luminescence (CPL) properties were investigated for optically pure samples. Density functional theory (DFT) calculations were conducted to further understand their photophysical properties including chiroptical responses.

External magnetic field-induced circularly polarized luminescence and electroluminescence from optically inactive thermally activated delayed fluorescence material 4CzIPN.

An achiral optically inactive organic luminophore, 4CzIPN, exhibits circularly polarized thermally activated delayed fluorescence when photoexcited under an external magnetic field. By embedding this luminophore in an active emission layer, an external-magnetic-field-induced circularly polarized electroluminescent device is developed in this study. The Faraday geometry of the applied magnetic field completely controls the direction of rotation of 4CzIPN-derived circularly polarized luminescence and electroluminescence.

Pressure-Responsive Polymer Chemosensors for Hydrostatic-Pressure-Signal Detection: Poly-l-Lysine-Pyrene Conjugates.

Stimulus-responsive polymer materials are an attractive alternative to conventional supramolecular and polymer assemblies for applications in sensing, imaging, and drug-delivery systems. Herein, we synthesized a series of pyrene-labeled α- and ε-poly-l-lysine conjugates with varying degrees of substitution (DSs). Hydrostatic-pressure-UV/vis, fluorescence, and excitation spectroscopies and fluorescence lifetime measurements revealed ground-state conformers and excited-state ensembles emitting fluorescence with variable intensities. The polylysine-based chemosensors demonstrated diverse ratiometric responses to hydrostatic pressure through adjustments in polar solvents, DSs, and polymer backbones. Additionally, the fluorescence chemosensor exhibited a promising glum value of 3.2 × 10-3, indicating potential applications in chiral fluorescent materials. This study offers valuable insights into the development of smart hydrostatic-pressure-responsive polymer materials.

Chiroptical Response Control of Planar and Axially Chiral Polymethylene-Vaulted Platinum(II) Complexes Bearing 1,1'-Binaphthyl Frameworks.

In this study, the synthesis, structure, and chiroptical response control of planar chiral polymethylene-vaulted trans-bis[(ß-iminomethyl)aryloxy]platinum(II) complexes bearing axially chiral 1,1'-binaphthyl ligands are described. A series of enantiopure polymethylene (n = 4-10)-vaulted complexes were prepared in 6 steps using commercially available (R)- or (S)-BINOL as the starting material without an optical resolution process. The trans-coordination and three-dimensional vaulted structures of the platinum complexes were elucidated from X-ray diffraction (XRD) studies. The complexes were found to show structural dependence of chiroptical responses in the dilute solution state such that the absolute values of [α]D, dissymmetry factors gabs in circular dichroism (CD), and glum in circularly polarized luminescence (CPL) increased upon shortening the length of the polymethylene bridges. The enhanced chiroptical responses were theoretically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, and the results are discussed in terms of the molecular structures and transition dipole moments of the ground states. The structural dependence of the chiroptical responses was ascribed to the distortion of the coordination platforms caused by restriction of the vaulting methylene linkers.

Chiral B-N AIEgens: Intense Blue Circularly Polarized Luminescence and Piezochromism.

We present a new class of blue circularly polarized luminescent emitters based on tetraarylaminoborane (TAAB) with considerable dissymmetry factor in the solid state. The chiral pendant 1-phenylethylamine in BN-RR and BN-SS imparts chirality to the core chromophore, resulting in circularly polarized luminescence signals (glum = 0.8 × 10-3) with a quantum yield of 33% in the crystalline state. This novel set of compounds also showcases intriguing thermally reversible piezochromism.

Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes.

Circularly polarized luminescence (CPL) features of BINOL-decorated cyclotriphosphazenes (CPs) are reported for the first time. The luminescence dissymmetry factor (glum ) of these compounds in chloroform solutions and polymethyl methacrylate (PMMA) thin films with wt 1 % doping concentrations are found to be 1.0×10-3 , and 2.9×10-3 , respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (CP-(R)/CP-(S)) show ultraviolet photoluminescence (~350-360 nm) in solution and the solid state. These compounds show ~10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In the solid state, CP-(R) shows larger PLQY than binaphthol-(R); in contrast, the S enantiomer shows lower PLQY than binaphthol-(S); this indicates that the isomer-dependent solid-state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room-temperature phosphorescence (pRTP) due to concentration-caused quenching. However, thin films with wt 1 % of these chiral emitters exhibit pRTP characteristics with a ~159-343 ms lifetime under vacuum. Theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.

Circularly polarised luminescence from excimer emission of anthracene derivatives complexed with γ-cyclodextrin in the solid state.

In this study, we report circularly polarised luminescence (CPL)-active molecules that exhibit high fluorescence quantum yields in the solid state. We developed anthracene derivatives with substituents at the 9 and 10 positions, such as ethyl(anthracene-9-carbonyl)glycinate (9AnGlyEt), N-butylanthracene-9-carboxamide (9AnB), N-benzylanthracene-9-carboxamide (9AnPh), and N 9,N 10-dibutylanthracene-9,10-dicarboxamide (9,10AnB). These compounds were complexed with γ-cyclodextrin (γ-CD) in the solid state by grinding, and the fluorescence properties of the resulting γ-CD complexes were investigated. The fluorescence quantum yields were enhanced after γ-CD complexation. Among the prepared γ-CD complexes, 9AnGlyEt/γ-CD had the highest fluorescence quantum yield (Φ f = 0.35), which was enhanced up to 5.8 times after γ-CD complexation. This was probably due to the interaction between the two anthracene molecules in the γ-CD cavity, which prevented fluorescence quenching caused by aggregation of the compounds. Positive CPL of g CPL = 1.3 × 10-3 was observed for 9AnGlyEt/γ-CD based on its excimer emission.