Circularly polarized luminescence induced by excimer based on pyrene-modified binaphthol

A new chiral bromobinaphthol-pyrene compound was developed to achieve a green circularly polarized luminescence (CPL) from its excimer with a dissymmetry factor (|g_lum|) value of 4.3 × 10⁻³ and a high quantum yield Φ_{F, solid} up to 55.9%, while no CPL signals could be observed for the blue luminescence from unimolecule. Meanwhile, reversal CPL signals can be observed from both concentrated solution and solid     

Multistate Aggregation-Induced Chiroptical Properties of Enantiopure Disulfide-Mediated Bispyrene Macrocycles

A chiral bispyrene macrocycle designed for exclusive intermolecular excimer fluorescence upon aggregation was synthesized by a double hydrothiolation of a bis-enol ether macrocycle followed by intramolecular oxidation of free thiols. Unusually high stereoselectivity was achieved for the thiol-ene additions under templated conditions and Et₃B/O₂ radical initiation. After enantiomer separation (chiral stationary phase HPLC), aqueous conditions provoked aggregation. Detailed structural evolution was afforded by ECD/CPL monitoring. Three regimes can be observed and characterized by strong modifications in chiroptical patterns under, at, or above a 70 % H₂O : THF threshold. In luminescence, high g_lum dissymmetry factors values were obtained, up to 0.022, as well as a double sign inversion of CPL signals during the aggregation, a behavior rationalized by time-dependent density functional theory (TDDFT) calculations. Langmuir layers of enantiopure disulfide macrocycles were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by AFM and UV/ECD/fluorescence/CPL.     

Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

With our new home‐built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi‐isomeric BODIPY DYEmers 1 and 2 , endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π–π* transitions (550–560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra (g_lum=4×10^?3) well reproduced by TD‐DFT and SCS‐CC2 (spin‐component scaled second‐order approximate coupled‐cluster) calculations using DFT‐optimized ground‐ and excited‐state structures. Compound 2 has weaker ECD and CPL spectra (g_lum=4×10^?4), partly due to the mutual cancellation of electric–electric and electric–magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited‐state geometries, we predicted the wrong sign for the CPL band of 2 using TD‐DFT with the most recommended hybrid and range‐separated functionals, whereas SCS‐CC2 or a DFT functional with full exact exchange provided the correct sign.     

Near-Infrared Circularly Polarized Luminescence through Intramolecular Excimer Formation of Oligo(p-phenyleneethynylene)-Based Double Helicates

Carbon-based double helicates consisting of two anthracene-containing oligo(p-phenyleneethynylene) units and two flexible chiral 1,1′-binaphthyl units or two rigid chiral 9,9′-spirobifluorene units were developed. The curved oligo(p-phenyleneethynylene) fragments in the double helicates were successfully constructed by tin-mediated reductive aromatization. Helical oligo(p-phenyleneethynylene) double strands fixed by two rigid spirobifluorene units showed little structural change under photoirradiation, thereby emitting circularly polarized luminescence (CPL) in the visible region with a high quantum yield (Φ_PL=0.93). In contrast, flexible binaphthyl units induced dynamic structural change of the oligo(p-phenyleneethynylene) luminophores under photoirradiation, leading to strong CPL (|g_lum|=1.1×10⁻²) in the near-infrared (NIR) region. UV/Vis, circular dichroism (CD), CPL and NMR spectroscopic analyses of the binaphthyl-hinged double helicate suggested excimer formation between two π-conjugated strands in the excited state. Theoretical calculations highlight the importance of the tightly interlocked excimer structure of the carbon-based double helicate in controlling the angle between the electric and magnetic transition dipole moments for strong NIR CPL generation.     

Circularly polarized luminescence from pyrene excimers

Recently, many reports have emerged about circularly polarized luminescence (CPL) based on excimer emission of pyrenes. The intense CPL was observed from various pyrene derivatives such as pyrenes having chiral side chains, chiral oligomers bearing multiple pyrene rings, and pyrenes encapsulated by γ-cyclodextrins. The luminescence dissymmetry factor was found to be obviously higher than the absorption one in those pyrenes. In addition, several pyrenes revealed reversible “on-off” CPL switching upon the complexation/decomplexation of metal ions.     

Yellow Circularly Polarized Luminescence from C1‐Symmetrical Copper(I) Complexes

The synthesis of chiral C₁‐symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10^?3. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL‐emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.     

Yellow Circularly Polarized Luminescence from C1-Symmetrical Copper(I) Complexes

The synthesis of chiral C₁-symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10⁻³. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL-emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.     

Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene) Aggregate in the Excited State

We prepared enantiomers of chiral Pt^II complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π–π* emission of the monomer but large for MMLCT (metal‐metal‐to‐ligand charge‐transfer) of the excimer and trimer which had a helical structure induced in a face‐to‐face stacking fashion. The trimer CPL for (+)‐Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)‐Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited‐state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD‐DFT calculations it was predicted that the dihedral angle θ(Cl‐Pt‐Pt‐Cl) was 50–60° or 110–140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.     

The synthesis and applications of asymmetric phase-transfer catalysts derived from isomannide and isosorbide

We report herein the synthesis of various derivatives of isomannide and isosorbide. Alkylation on N-(diphenylmethylene)glycine tert-butyl ester show the new catalysts to be effective phase-transfer catalysts with moderately good enantioselectivity. The effect of exo and endo substituents on the enantioselectivity of alkylation reaction have also been studied.     

Helically Assembled Pyrene Arrays on an RNA Duplex That Exhibit Circularly Polarized Luminescence with Excimer Formation

Circularly polarized luminescence (CPL) was observed in pyrene zipper arrays helically arranged on an RNA duplex. Hybridization of complementary RNA strands having multiple (two to five) 2′‐O‐pyrenylmethyl modified nucleosides affords an RNA duplex with normal thermal stability. The pyrene fluorophores are assembled like a zipper in a well‐defined helical manner along the axis of RNA duplex, which, upon 350 nm UV illumination, resulted in CPL emission with pyrene excimer formation. CPL (g_lum) levels observed for the pyrene arrays in dilute aqueous solution were +2×10^?2–+3.5×10^?2, which are comparable with |g_lum| for chiral organic molecules and related systems. The positive CPL signals are consistent with a right‐handed helical structure. Temperature dependence on CPL emission indicates that the stable rigid RNA structure is responsible for the strong CPL signals. The single pyrene‐modified RNA duplex did not show any CPL signal.     

Improved automated simultaneous determination of isosorbide dinitrate and its metabolites in plasma by capillary column gas chromatography

An automated specific and sensitive method for the simultaneous determination of isosorbide dinitrate and its metabolites isosorbide-2-mononitrate, isosorbide-5-mononitrate, isomannide mononitrate, and isoidide mononitrate at concentrations down to 0.5, 1, 3, 2, and 2 ng/ml, respectively, in human plasma is described. The procedure involves the extraction of the drug and its metabolites together with their internal standards isomannide dinitrate and o-nitrobenzyl alcohol from plasma with dicholromethane. The analysis is carried out by fused silica capillary gas chromatography using a ⁶³Ni-electron capture detector. The method is applied to the pharmacokinetics of isosorbide dinitrate in humans.     

Circularly polarized luminescence induced by excimer based on pyrene-modified binaphthol

A new chiral bromobinaphthol-pyrene compound was developed to achieve a green circularly polarized luminescence (CPL) from its excimer with a dissymmetry factor (|g_lum|) value of 4.3×10^-3 and a high quantum yield Φ_{F, solid} up to 55.9%, while no CPL signals could be observed for the blue luminescence from unimolecule. Meanwhile, reversal CPL signals can be observed from both concentrated solution and solid.     

Thioflavin T: Electronic Circular Dichroism and Circularly Polarized Luminescence Induced by Amyloid Fibrils

The circularly polarized luminescence (CPL) spectrum of thioflavin T (ThT) bound to insulin amyloid fibrils has been measured for the first time. It has been found that the samples exhibiting induced circular dichroism (CD) retain the optical activity in the CPL spectra, with the same sign of the rotatory strength. The fluorescence dissymmetry factor is substantial (of the order of magnitude 10^?2). Unlike in the corresponding CD and absorption spectra, there is no shift of the CPL band with respect to the fluorescence band. It has been verified that the measured CPL spectra are free from artifacts from circularly polarized scattering of emitted light by conducting additional measurements in a medium with a refractive index similar to insulin (methylsalicylate). The CD and CPL spectra have been interpreted by means of density functional calculations carried out for ThT in its ground and first excited states in different dielectric environments and for ThT interacting with an aromatic ring. It has been found that the presence of an aromatic ring close to the ThT molecule induces Cotton effects of the same order of magnitude as the stabilization of one enantiomeric conformer. Thus, it is expected that both mechanisms contribute to the induced CD and CPL effect to a similar degree.     

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (g_lum), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large g_lum values up to around ±1×10⁻². The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their g_lum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.     

Detection of Circularly Polarized Luminescence of a Cs‐EuIII Complex in Raman Optical Activity Experiments

Circularly polarized luminescence (CPL) spectra are extremely sensitive to molecular structure. However, conventional CPL measurements are difficult and require expensive instrumentation. As an alternative, we explore CPL using Raman scattering and Raman optical activity (ROA) spectroscopy. The cesium tetrakis(3‐heptafluoro‐butylryl‐(+)‐camphorato) europium(III) complex was chosen as a model as it is known to exhibit very large CPL dissymmetry ratio. The fluorescent bands could be discriminated from true Raman signals by comparison of spectra acquired with different laser excitation wavelengths. Furthermore, the ROA technique enables fluorescence identification by measuring the degree of circularity. The CPL dissymmetry ratio was measured as the ROA circular intensity difference of 0.71, the largest one ever reported. The alternative CPL measurement enhances applications of lanthanides in analytical chemistry and chemical imaging of biological objects.     

Turn-on Circularly Polarized Luminescence in Chiral Indium Chlorides by 5s2 Metal Centers

Introducing chirality into the metal-halide hybrids has enabled many emerging properties including chiroptical activity, spin-dependent transport, and ferroelectricity. However, most of the chiral metal-halide hybrids to date are non-emissive, and the underlying mechanism remains elusive. Here, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal-halide hybrids. We demonstrate that alloying Sb³⁺ into chiral indium-chloride hybrids dramatically increases the photoluminescence quantum yield in two new series of chiral indium-antimony chlorides. These materials exhibit strong CPL signals with tunable energy and a high dissymmetry factor up to 1.5×10⁻². Mechanistic studies reveal that the emission originates from the self-trapped excitons centered in 5s² Sb³⁺. Moreover, near-ultraviolet pumped white light is demonstrated with a polarization up to 6.0 %. Our work demonstrates new strategies towards highly luminescent chiral metal-halide hybrids.     

Multiply Twisted Chiral Macrocycles Clamped by Tethered Binaphthyls Exhibiting High Circularly Polarized Luminescence Brightness

Chiral macrocyclic dimers, trimers, and tetramers composed of paraphenylene and tethered binaphthyl were synthesized, and their molecular structures and chiroptical properties were investigated. X-ray analysis and theoretical calculations revealed that multiple twisted molecular structures – dimers, trimers, and tetramers – adopt figure-of-eight, Möbius triangle, and concave rectangle structures, respectively. These homologues have large ϵ values in their UV-vis absorption spectra because of the π-conjugation of the naphthalene-phenylene-naphthalene frameworks. Owing to the shape-persistent ring structure and tethering with −OCH₂CH₂O−, high fluorescence quantum yields and a relatively high dissymmetry factor g_CPL in circularly polarized luminescence (CPL) spectra were achieved. This results in CPL brightness (B_CPL) of over 100, which is greater than that of the conventional organic CPL dye.     

Nanosized Carbon Macrocycles Based on a Planar Chiral Pseudo Meta-[2.2]Paracyclophane

Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical-active chiral macrocycles with intriguing properties. X-ray crystal analysis revealed aesthetic necklace-shaped structures and size-dependent packages with long-range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size-dependent chiroptical properties with moderately large CPL dissymmetry factor of 10⁻³ and CPL brightness in the range of 30–40 M⁻¹ cm⁻¹ were observed.     

Circularly Polarized Luminescence of Aluminum Complexes for Chiral Sensing of Amino Acid and Amino Alcohol

Determination of the absolute configuration (AC) of chiral molecules is a key issue in many fields related to chirality such as drug development, the asymmetric reaction screening, and the structure determination of natural compounds. Although various methods, such as X‐ray crystallography and NMR spectroscopy, are used to determine the AC, a simple and cheap alternative method is always anticipated. So far, electronic circular dichroism (ECD) spectroscopy has been widely used to ascertain the AC and enantiomeric excess (ee) values by applying appropriate organic probes. Here, circularly polarized luminescence (CPL) spectroscopy was applied to determine the AC and ee values of a series of amino acid and amino alcohol. The measurements were conducted by mixing the amino acids or amino alcohols with an achiral 1‐hydroxy‐2‐naphthaldehyde. Upon in situ formation of the Schiff base complexes, the system showed emission enhancement and CPL in the presence of Al³⁺, whose intensity and sign can be used to assign the chiral sense of the amino acids and amino alcohols. The authenticity of the method was further compared with the established CD spectroscopy, revealing that CPL spectra of formed Al³⁺ complex were effective to determine the AC of chiral species.