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

Host-Guest Complexation-Induced Aggregation Based on Pyrene-Modified Cyclodextrins for Improved Electronic Circular Dichroism and Circularly Polarized Luminescence

Several γ-cyclodextrin (CD) derivatives mono- or di-substituted by pyrenes at the primary rim of the CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into γ-CD cavities. The hydrophobic complexation-induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) activities, giving unprecedently high g_abs and g_lum values up to 4.3×10^-2 and 5.3×10^-2 , respectively. The aggregates lead to excimer emission with high quantum yields and show B_CPL and Bⁱ _CPL up to 338. 6 M^-1  cm^-1 and 169.3 M^-1  cm^-1 , respectively.

Cyclodextrins with Multiple Pyrenyl Groups: An Approach to Organic Molecules Exhibiting Bright Excimer Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) has attracted much attention because of its potential for electronic and biological applications. Herein, we report a simple and effective approach to organic molecules exhibiting bright CPL by combining a chiral cyclic molecular scaffold and multiple excimer-enabling moieties. An a-cyclodextrin ( CyD ) scaffold was modified with six pyrenyl groups to obtain pyrene-cyclodextrins ( PCD s) in a one-step synthesis from commercially available compounds. The PCDs exhibited high molar extinction coefficients (ε ~ 10 5 M -1 cm -1 ), polarized emission with a good dissymmetry factor (| g lum | ~ 10 -2 ), and quantum yield ( Φ f ~ 0.5). Owing to the excellent photophysical properties of the PCDs, the circularly polarized luminescence brightness ( B CPL ) reached 340 M -1 cm -1 . Comprehensive photophysical and chiroptical studies of the PCD s with only five pyrene units and with linkers of various lengths connecting the CyD with the pyrene units revealed that the formation of a pyrene excimer in a spatially crowded environment is crucial for CPL anisotropy. This study paves the way for the development of bright CPL organic molecules.

Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule

A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90° exhibit (-)- and (+)-CPL, respectively.

A Pyrene-Modified Serinol Nucleic Acid Nanostructure Converts the Chirality of Threoninol Nucleic Acids into Circularly Polarized Luminescence Signals

Herein is reported a circularly polarized luminescent (CPL) probe that can respond to the chirality of nucleic acids. An achiral nanostructure was prepared by the hybridization of symmetric serinol nucleic acid (SNA) containing pyrene-modified residues. When chiral oligomers that were complementary to the SNA were added, they induced helicity into the SNA nanowire. Efficient circular dichroism (CD) signal amplification was observed when pyrene was attached to uracil bases through a rigid alkynyl linker. Both CPL and CD signals were observed; they depended on the chirality of the added acyclic threoninol nucleic acid (aTNA) oligomer. This system can be used to convert the chirality of chiral biomolecules into chiroptical signals.

Chiral V-shaped Pyrenes: Hexagonal Packing, Superhelix, and Amplified Chiroptical Performance

Here, we designed symmetric and dissymmetric chiral V-shaped pyrenes by linking achiral pyrenes to trans-1,2-cyclohexane diamine scaffolds with varied spacers to investigate their circular dichroism (CD) and circularly polarized excimer emission (CPEE). In molecular solution, the symmetric V-shaped molecules (P1, P2, P3) displayed spacer-dependent CD and CPEE originating from the intramolecular excimers while the dissymmetric V-shaped B was silent in CD and CPEE. Upon self-assembly, the chiral V-shaped conformation guided a helical hexagonal packing. Notably, P1 self-assembled into delicate superhelices with optimum chiroptical activities and the largest g_CD for pyrene derivatives to date. The dissymmetric B formed two distinct hexagonal aggregates as twists and rectangular nanotubes with greatly amplified CPEE. This work demonstrates unprecedented hexagonal superhelices from chiral V-shaped scaffolds and provides a deep insight into the relationship between molecular conformation, supramolecular architectures, and their chiroptical performance.

Inversing supramolecular chirality and boosting circularly polarized luminescence of pyrene moieties via a gel matrix

Alkyl-substituted l/d-glutamide derivatives (L/D-SG) were designed as gelators to fabricate host gel matrices. Pyrene-appended l/d-glutamide derivatives (Py-LG/Py-DG) were employed as guest luminophores to investigate chiral packing and emission behavior in gel matrices. It was found that Py-LG and Py-DG are prone to form P- and M-chirally packed assemblies in DMSO gels, respectively. However, the chiral packing was inversed, and CPL was boosted after Py-LG/Py-DG was embedded in the L/D-SG gel matrix. M-chiral packing together with left-handed excimer emission ((-)-CPL) was observed in the Py-LG immobilized L-SG gel matrix, while P-chiral packing together with right-handed excimer emission ((+)-CPL) was found in the Py-DG immobilized L-SG gel matrix. It is more interesting to find that the molecular chirality of the matrix gelator did not affect the supramolecular chirality of pyrene assemblies. Either l or a d-matrix gelator can inverse the supramolecular chirality of the pure gel, but did not follow the chirality of the matrix. It was found that the gel matrix converts intralayer pyrene-pyrene (Py-Py) packing in the pure pyrene gel to interlayer Py-Py packing, thus giving an opposite chirality. The study not only deepened our understanding of the supramolecular chirality transfer but also unveiled the effects of an inert gel matrix in regulating the chiroptical properties.

Not by Serendipity: Rationally Designed Reversible Temperature-Responsive Circularly Polarized Luminescence Inversion by Coupling Two Scenarios of Harata-Kodaka's Rule

Intelligent control over the handedness of circularly polarized luminescence (CPL) is of special significance in smart optoelectronics, information storage, and data encryption; however, it still remains a great challenge to rationally design a CPL material that displays reversible handedness inversion without changing the system composition. Herein, we show this comes true by coupling the two scenarios of Harata-Kodaka's rule on the same supramolecular platform of crystalline microtubes self-assembled from surfactant-cyclodextrin host-guest complexes. Upon coassembling a linear dye with its electronic transition dipole moment outside of the cavity of β-CyD, the chirality transfer from the induced chirality of SDS in the SDS@2β-CyD microtubes to the dye generates left-handed CPL at room temperature. Upon elevating temperature, the dye forms inclusion complex with β-CyD, so that right-handed CPL is induced because the polar group of the dye is outside of the cavity of β-CyD. This process is completely reversible. We envision that host-guest chemistry would be very promising in creating smart CPL inversion materials for a vast number of applications.

Template Assisted Generation of Chiral Luminescence in Organic Fluorophores

Development of efficient ways of fabricating chiral light emitting materials is an active area of research due to the vast potential offered by these materials in the field of optoelectronic devices, data storage, and asymmetric synthesis. Among the various methods employed, template assisted generation of chiral luminescence is gaining enormous attention due to its simplicity, applicability over a wide range of fluorescent molecules/dyes, and the display of high anisotropic values.

Influence of chirality on fluorescence and resonance energy transfer

Electronically excited molecules frequently exhibit two distinctive decay mechanisms that rapidly generate optical emission: one is direct fluorescence and the other is energy transfer to a neighboring component. In the latter, the process leading to the ensuing "indirect" fluorescence is known as FRET, or fluorescence resonance energy transfer. For chiral molecules, both fluorescence and FRET exhibit discriminatory behavior with respect to optical and material handedness. While chiral effects such as circular dichroism are well known, as too is chiral discrimination for FRET in isolation, this article presents a study on a stepwise mechanism that involves both. Chirally sensitive processes follow excitation through the absorption of circularly polarized light and are manifest in either direct or indirect fluorescence. Following recent studies setting down the symmetry principles, this analysis provides a rigorous, quantum outlook that complements and expands on these works. Circumventing expressions that contain complicated tensorial components, our results are amenable for determining representative numerical values for the relative importance of the various coupling processes. We discover that circular dichroism exerts a major influence on both fluorescence and FRET, and resolving the engagement of chirality in each component reveals the distinct roles of absorption and emission by, and between, donor and acceptor pairs. It emerges that chiral discrimination in the FRET stage is not, as might have been expected, the main arbiter in the stepwise mechanism. In the concluding discussion on various concepts, attention is focused on the validity of helicity transfer in FRET.

Observation of Circularly Polarized Luminescence of the Excimer from Two Perylene Cores in the Form of [4]Rotaxane

A perylene-based [4]rotaxane was synthesized by the Sonogashira coupling of the 2:2 inclusion complex consisting of two alkynylperylenes and two γ-cyclodextrins with terphenyl-type stopper molecules. The [4]rotaxane showed orange emission attributable to the spatially restricted alkynylperylene excimer with a high fluorescence quantum yield of Φ_f =0.15. The excimer emission was circularly polarized as a result of the asymmetrically twisted perylene pair under the influence of chirality of γ-cyclodextrin. The g_lum value of the excimer emission was determined to be -2.1×10^-2 at 573 nm, as large as those of the corresponding known pyrene-based series. This is the first example, in which circularly polarized luminescence was clearly observed from the excimer of a pair of perylene cores.

Combined reversible switching of ECD and quenching of CPL with chiral fluorescent macrocycles

A series of chiral fluorescent macrocycles display a remarkable combination of both +/– ECD and strong on/off CPL reversible switching upon cation binding and displacement.

Straightforward synthesis and resolution of a series of chiral fluorescent macrocycles are presented, together with their electronic circular dichroism (ECD), strong excimer fluorescence (EF, λ 300 to 650 nm) and allied highly circularly polarized luminescence (CPL, g_lum up to 1.7 × 10^–2). The ECD, EF and CPL responses are strongly affected by the presence of metal ions (Na⁺, Ba²⁺) thanks to deep conformational changes. While ECD signals can be almost completely reversibly inverted upon the complexation/decomplexation of metal ions in a typical binary response, CPL signals are reversibly quenched concomitantly. The designed macrocycles display thus a remarkable combination of both +/– ECD and on/off CPL reversible switching.

Circularly Polarized Luminescence from a Pyrene-Cyclodextrin Supra-Dendron

Soft nanomaterials with circularly polarized luminescence (CPL) have been currently attracting great interest. Here, we report a pyrene-containing π-peptide dendron hydrogel, which shows 1D and 2D nanostructures with varied CPL activities. It was found that the individual dendrons formed hydrogels in a wide pH range (3-12) and self-assembled into helices with pH-tuned pitches. Through chirality transfer, the pyrene unit could show CPL originated from both the monomer and excimer bands. When cyclodextrin was introduced, different supra-dendrons were obtained with β-cyclodextrin (PGAc@β-CD) and γ-cyclodextrin (PGAc@γ-CD) through host-guest interactions, respectively. Interestingly, the PGAc@β-CD and PGAc@γ-CD supra-dendrons self-assembled into 2D nanosheet and entangled nanofibers, respectively, showing cyclodextrin induced circularly polarized emission from both the monomer and excimer bands of the pyrene moiety. Thus, through a simple host-guest interaction, both the nanostructures and the chiroptical activities could be modulated.

Intense excimer CPL of pyrenes linked to a quaternaphthyl

(R,R,R)-Quaternaphthyl possessing multiple pyrenes emits CPL with high Φ_FL and g_lum values both in solution and in the solid state.

Recent Advances in Nucleic Acid Targeting Probes and Supramolecular Constructs Based on Pyrene-Modified Oligonucleotides

In this review, we summarize the recent advances in the use of pyrene-modified oligonucleotides as a platform for functional nucleic acid-based constructs. Pyrene is of special interest for the development of nucleic acid-based tools due to its unique fluorescent properties (sensitivity of fluorescence to the microenvironment, ability to form excimers and exciplexes, long fluorescence lifetime, high quantum yield), ability to intercalate into the nucleic acid duplex, to act as a π-π-stacking (including anchoring) moiety, and others. These properties of pyrene have been used to construct novel sensitive fluorescent probes for the sequence-specific detection of nucleic acids and the discrimination of single nucleotide polymorphisms (SNPs), aptamer-based biosensors, agents for binding of double-stranded DNAs, and building blocks for supramolecular complexes. Special attention is paid to the influence of the design of pyrene-modified oligonucleotides on their properties, i.e., the structure-function relationships. The perspectives for the applications of pyrene-modified oligonucleotides in biomolecular studies, diagnostics, and nanotechnology are discussed.

Chiral triptycene-pyrene π-conjugated chromophores with circularly polarized luminescence

Novel chiral triptycenes showing circularly polarized luminescence based on the supramolecular chirality induced in the hydrogen-bonded aggregate have been developed.

Anomalous photovoltaic effect based on molecular chirality: influence of enantiomeric purity on the photocurrent response in π-conjugated ferroelectric liquid crystals

Photovoltaic effect based on molecular chirality was observed in π-conjugated ferroelectric liquid crystals.

Circularly polarized luminescence reveals interaction between commercial stains and protein matrices used in paintings

Here we show that circularly polarized luminescence (CPL) can give unique insight into interactions between fluorescent commercial stains and protein-based materials used in painting. CPL can complement information from ECD and fluorescence.