Controlled packing of chiral assembly scaffolds to promote chiral J-aggregation of carbocyanine dyes.

Controlled aggregation of dyes is crucial to achieve their desired optical and electronic properties. Here, we report the induction of chiral J-aggregation of carbocyanine dyes by using lysine-derived amphiphile assemblies as scaffolds in water. The molecular structure of the amphiphiles affected the packing of the assembly. The tight packing with some flexibility promoted the formation of J-aggregates of the dyes with strong chiroptical properties.

Sequential chiral induction between organic and inorganic supramolecular helical assemblies for the in situ formation of chiral carbon dots.

Self-organised helical bilayers of dicationic gemini surfactants confined in helical silica nanospace were transformed in situ to carbon dots (CDots) via pyrolysis. These water-dispersible CDots exhibit electronic absorption spanning the UV and visible range and possess symmetrical circular dichroism (CD) signals, the sign of which depends on the handedness of the helices.

Chiral H-aggregation-induced large stokes shift with CPL generation assisted by α-helical poly(L-lysine) substructure.

Fluorescent materials with large Stokes shifts have significant potential for use in optical applications. Typically, a synthetic design strategy is utilized for this purpose. In this study, we demonstrated a novel method by binding a chiral template to a nonchiral fluorescent agent without chemical modification. Specifically, α-helical poly(L-lysine) was employed as the chiral template, which interacted with a disulfonic fluorescent dye, such as NK2751. The dye caused excimer luminescence by inducing the formation of a chirally H-aggregated dimer only when poly(L-lysine) was in an α-helical shape. The result was a Stokes shift of 230 nm. Similar effects were not observed when the chiral template was in a random coil condition and the Stokes shift was less than 40 nm. These findings imply that H-aggregated dimerization, which often results in quenching, permits the electronic transitions necessary for fluorescence events by the formation of the chirally twisted state. In addition, we introduce for the first time the generation of circularly polarized luminescence using the chirality induction phenomena in a dye supported by poly(L-lysine).

Chemical redox-induced chiroptical switching of supramolecular assemblies of viologens.

A chiral supramolecular assembly exhibiting redox-induced changes in its chiroptical properties was prepared using viologen-modified glutamide (G-V2+) derivatives. Achiral viologen moieties in the G-V2+ assembly were chirally orientated by glutamide groups, affording a unique orange-colored solution, with a visible absorption band at around 470 nm, having electronic circular dichroism (CD) signals (molar ellipticity [θ] = 0.58 × 105 deg cm2 dmol-1: absorption dissymmetry factors (g) = 5.2 × 10-3 at 512 nm). The G-V2+ could be reduced to its cation radical (G-V+˙) but retains its chiral assembly. After chemical reduction, the color change from orange to blueish violet, indicating an absorption band at approximately 560 nm, and the sign change of the CD signal from positive to negative ([θ] = -0.36 × 105 deg cm2 dmol-1; g = -2.9 × 10-3 at 580 nm) were observed in water. Subsequent oxidation re-introduces the G-V2+ chiroptical behavior before reduction.

Helically aligned fused carbon hollow nanospheres with chiral discrimination ability.

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe3O4 nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Chiral optical scattering from helical and twisted silica nanoribbons.

Helical and twisted silica nanoribbons, deposited in an in-plane direction and with a random orientation, on a quartz substrate showed chiral optical scattering, and the helical nanoribbons had a g-factor of the order of 10-2 below 250 nm. Their signs depend on the handedness of the nanohelices. The effect of the morphology and the orientation of the helices on the chiral optical scattering were investigated with simulations via the boundary element method.

Lanthanide ion-doped silica nanohelix: a helical inorganic network acts as a chiral source for metal ions.

We demonstrate that lanthanide ions doped in nanometrical silica helices with a chirally arranged siloxane network without any organic mediates show induced chiroptical properties such as circular dichroism and circularly polarized luminescence.

Chirality induction on non-chiral dye-linked polysilsesquioxane in nanohelical structures.

We demonstrate the direct induction of chirally arranged organic dye-linked polysilsesquioxane through a sol-gel transcription using a chiral supramolecular template. The chiral arrangement was confirmed by using electronic and vibrational circular dichroism and circularly polarized luminescence spectroscopies.

Extreme enhancement of secondary chirality through coordination-driven steric changes of terpyridyl ligand in glutamide-based molecular gels.

Aggregation-induced chirality is potentially useful in sensor technology applications. Herein we show extreme enhancement of secondary chirality through coordination-driven steric changes of terpyridyl ligand in molecular gels. The secondary chirality reflecting on enhancement of chiral signals (i.e., circular dichroism (CD) and circularly polarised luminescence (CPL)) of the molecular gels formed from glutamide-attached terpyridine (G-tpy) is extremely enhanced by the coordination of its terpyridyl groups to metal ions such as Cu2+, Zn2+ and Ru2+, which is due to dramatic changes in the stacked structure of the chromophore groups through the formation of metal ion complex. Metal-free terpyridine exists in a non-planar geometry, which suppress π-π stacking interactions among aggregates. The planarity of the terpyridyl group is improved through metal-ion complexation, which induces the metal-ion-coordinated terpyridyl groups to stack. The thermal stabilities of the CD signals are strongly affected by the metal-ion species. CPL signal is generated in the molecular gel formed from G-tpy-Zn2+ complex accompanied by chelation-enhanced fluorescence. It is expected that large and sensitive coordination-driven secondary chirality signals (CD and CPL) are useful for sensing guest molecules and the surrounding environment.

Induced circular dichroism of monoatomic anions: silica-assisted the transfer of chiral environment from molecular assembled nanohelices to halide ions.

We demonstrate the first example of induced CD of monoatomic anions. This was detected using chirally-arranged molecular assemblies of non-chiral cationic gemini surfactants (16-2-16) with monoatomic anions stabilized with silica-coating. Furthermore, we have also achieved multi-step transfer of a chiral environment through an in situ chemical reaction via chiralized monoatomic anions.

Fluorescence emission originated from the H-aggregated cyanine dye with chiral gemini surfactant assemblies having a narrow absorption band and a remarkably large Stokes shift.

We demonstrate that the fluorescence emission that originated from a cyanine dye forming H-aggregates with a narrow absorption band and a remarkably large Stokes shift can be induced by symmetry breaking. The H-aggregate formation was successfully induced using chirally assembled cationic gemini surfactants with enantiomeric tartrate counterions as templates in water.

Direct Observation of Siloxane Chirality on Twisted and Helical Nanometric Amorphous Silica.

Synthesis of chiral inorganic or hybrid nanomaterials through sol-gel transcription of chiral organic templates has attracted a great deal of interest for more than a decade. However, the chiral nature of these inorganic matrices has never been directly observed. For the first time, we report a direct evaluation of chirality on noncrystalline silica chiral nanoribbons by vibrational circular dichroism (VCD) measurements. Strong Cotton effect around 1150-1000 cm-1 from Si-O-Si asymmetric stretching vibration was observed. Surprisingly, calcination of these hybrid nanoribbons doubled the intensity of Cotton effects. On the basis of transmission electron microscopy observations, IR, VCD, NMR, and Raman spectroscopies, we demonstrate that the silica chirality originates from twisted siloxane network composed of chiral arrangement of the Si-O-Si bonds. Our findings clearly prove the presence of chiral organization of amorphous silica network, making them very promising chiral platforms for chiral recognition, optical applications, or asymmetric catalysis.

Memorized chiral arrangement of gemini surfactant assemblies in nanometric hybrid organic-silica helices.

Hybrid nanohelices were obtained from silicification of self-assemblies of gemini surfactants with tartrate counterions. The chiral arrangement of these non-chiral gemini surfactants was preserved in the silica matrix even after the counterion exchange for a non-chiral bromide, and was capable of inducing the chiral organisation of a non-chiral dye, methyl orange.

Functionalization of methyl orange using cationic peptide amphiphile: colorimetric discrimination between ATP and ADP at pH 2.0.

A solvatochromic and non-fluorescent acid-base indicator, methyl orange (MO) was applied to colorimetric discrimination between adenosine triphosphate (ATP) and the corresponding diphosphate (ADP) at pH 2.0 in the presence of L-glutamic acid-derived cationic peptide amphiphile 1. This method is based on the fact that the amphiphile 1 can prevent MO from protonation even at pH 2.0. No similar colour change was observed when ADP was added instead of ATP under the same conditions. The effect of the molecular structure of several peptide amphiphiles and dyes was also investigated.

Molecular structural requirements, dye specificity, and application of anionic peptide amphiphiles that induce intense fluorescence in cationic dyes.

We have previously reported that a double-chain anionic amphiphile capable of intermolecular triple hydrogen bonds could form extremely hydrophobic sites in water and specifically incorporated stilbazolium-based compact hemicyanine dyes as monomeric species, resulting in induction of intense fluorescence emission in the dyes. In this paper, the structural requirements of the intense fluorescence-inducing amphiphiles were investigated. It is noted that the introduction of beta-Ala residues into two long-chain alkyl group moieties was most effective for the amphiphiles derived from L-glutamic acid with relatively shorter side-chain methylenes. The dye specificity in terms of induction of the intense fluorescence was also investigated using hemicyanines (stilbazolium etc.), cyanine, carbocyanine, thiacarbocyanines, and azo dye. The amphiphile with the shortest octanoyl-beta-alanyl double-chain alkyl groups, longer side-chain, and shorter spacer was found to show increased sensitivity to alkali metal ions, especially Li(+). This could be a potential OFF-ON type fluorescence sensor for Li(+).

Formation of specific dipolar microenvironments complementary to dipolar betaine dye by nonionic peptide lipids in nonpolar medium.

This paper describes the host-guest interaction between nonionic peptide lipids and solvatochromic dipolar betaine dyes in nonpolar aprotic organic solvent. We have serendipitously found that the colour of Reichardt's Dye (referred to as ET(30) hereafter, although the term ET(30) has been used as a polarity parameter) in chlorobenzene unusually blue-shifted in the presence of L-glutamic acid-derived peptide lipid 1 with a benzyloxycarbonylated Gly headgroup. Since it is widely accepted that ET(30) shows negative solvatochromism, i.e., the visible absorption band of this dye blue-shifts as the solvent polarity increases, the blue-shift indicates that ET(30) was in contact with the more polar microenvironment produced by the peptide lipid 1 rather than chlorobenzene under aggregate-free conditions. The binding site was assumed to be N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, i.e., the O- and N+ of ET(30) complementarily bound to N-H(delta+) and CO(delta-) through hydrogen bonding and ion-dipole interaction, respectively. Since ET(30) is practically non-fluorescent, it was not feasible to use fluorescence spectrometry, which is a powerful method for the study of host-guest interactions, in order to specify the binding mode of ET(30). Therefore, a synthetic approach, although very laborious but reliable, has been used in conjunction with solvatochromic probing using visible absorption spectroscopy to specify the binding site on peptide lipid 1. The binding site has been found to be located on two dipoles, i.e., N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, because introducing steric hindrance into the Gly moiety using several L-alpha-amino acids with bulky -substituents interfered with the binding of ET(30). Similar specific binding behaviour of ET(30) was observed by replacing the Gly residue of the lipid 1 with sarcosine (Sar). It was found that self-assembly of the peptide lipid was necessary for effective capture of ET(30). The molecular structural requirements of the peptide lipids that form such specific polar microenvironments complementary to dipolar betaine dyes have also been investigated.