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.     

Tunable Excimer Circularly Polarized Luminescence in Isohexide Derivatives from Renewable Resources

Organic compounds showing circularly polarized luminescence (CPL) are at the forefront of novel applications and technologies. Here we show the synthesis and chiroptical properties of pyrene and perylene derivatives of inexpensive chiral scaffolds: isomannide and isosorbide. Low-intensity ECD spectra were obtained, suggesting the absence of chromophore interaction in the ground state, except in the case of isomannide bis-perylenecarboxylate, whose ECD spectrum showed a positive exciton couplet. All isomannide derivatives, with the only exception of the one containing a pyrenecarboxylate and a perylenecarboxylate, exhibited excimer CPL spectra, whereas isosorbide derivatives did not show any CPL. Isomannide derivatives bearing two pyrenecarboxylate or two pyrenylacetate groups showed positive CPL emission with dissymmetry factors up to 10⁻², which depends on the conformational freedom of the appended units. The CPL sign, Stokes shift and order of magnitude of dissymmetry factor were reproduced by excited-state calculations on a representative compound. Interestingly, the mixed derivative containing pyrenic units with different spacing from the isomannide scaffold showed an oppositely signed excimer band with respect to the homo-substituted derivatives.     

Ring-Opened Hemiporphyrazines: Helical Molecules Exhibiting Circularly Polarized Luminescence

We designed and synthesized a new type of small helical molecule exhibiting intense circularly polarized luminescence (CPL) ( 1_2H ) by modifying a 20π-electron hemiporphyrazine with a large transition magnetic dipole moment. The hemiporphyrazine ring was opened and one additional pyridine unit was introduced, resulting in an overlap of two pyridine rings. X-ray structure analysis confirmed that 1_2H and its zinc complex ( 1_Zn ) adopt a helical geometry. A racemic mixture of 1_Zn was resolved into two enantiomers ((P)- and (M)- 1_Zn ), which exhibited CPL with a high luminescence dissymmetry factor (g_lum) value of ±2.1×10⁻². The origin of the large g_lum value was rationalized by means of DFT calculations. Helical structures could be formed in a diastereoselective manner by covalently attaching chiral units to the skeleton ( 1’_2H and 1’_Zn ). 1_Zn was found to possess chiral recognition ability for amines.     

Circularly Polarized Luminescence Switching in Small Organic Molecules

The circularly polarized luminescence (CPL) switching is of significant interest for applications in security technologies and sensing devices. Small organic molecules (SOMs) show several advantages over metal complexes, supramolecular assemblies, and polymers. Therefore, the recent progress on the CPL switching in SOMs is here reviewed. The results are summarized based on the strategies used to tune factors that influence the emission properties, and thus, to realize CPL switching. The strategies that have been adopted include promoting the excimer formation of fluorescent units, changing the conformation of fluorophores, tuning the electronic structure of the π-skeleton/substituent, and modulating the intramolecular charge-transfer dynamics.     

A Doubly Alkynylpyrene‐Threaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer

The Sonogashira coupling of γ‐CD‐encapsulated alkynylpyrenes with terphenyl‐type stopper molecules gave a doubly alkynylpyrene‐threaded [4]rotaxane. The rotaxane showed only excimer emission, with a high fluorescence quantum yield of Φ_f=0.37, arising from the spatially restricted excimer within the cavity of the γ‐CD. The excimer emission suffered little from self‐quenching up to a concentration of 1.5×10^?5 M and was circularly polarized with a high g_lum value of ?1.5×10^?2. The strong circularly polarized luminescence may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.     

Chiral Oligothiophenes with Remarkable Circularly Polarized Luminescence and Electroluminescence in Thin Films

This work reports the first observation of circularly polarized electroluminescence (CPEL) in thin films of self-organized oligothiophenes. Four new 1,4-phenylene and 9H-carbazole-based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthesized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed g_lum in the order of 10⁻² on a wide wavelengths range, originating from their self-organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularly-polarized organic light-emitting diodes (CP-OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP-OLED with active layer made only of a small organic compound.     

Multilevel Chirality Transfer from Amino Acid Derivatives to Circularly Polarized Luminescence-Active Nanoparticles in Aqueous Medium

Chirality at different levels is widely observed in nature, but the clue to connect it all together, and the way chirality transfers among different levels are still obscure. Herein, a l -/d -lysine-based self-assembly system was constructed, in which two-step chirality transfer among three different levels was observed in aqueous solution. The chirality originated from the point chirality of amino acid derivatives l -/d -PyLys hydrochloride, and was transferred to the planar conformational chirality of water-soluble pillar[5]arene pR-/pS-WP5. Then, with the aid of pR-/pS-WP5, nanoparticles were formed that exhibited L-/R-handed circularly polarized luminescence with a dissymmetry factor of up to ±0.001, arising from pyrene chiral excimers. This multilevel chirality transfer not only provides a perspective to trace potential clues, and to pursue certain ways by which the chirality transfers, but also offers a strategy to create controllable CPL emission in aqueous media.     

Circularly Polarized Luminescence from Helically Chiral N,N,O,O‐Boron‐Chelated Dipyrromethenes

Helically chiral N,N,O,O‐boron chelated dipyrromethenes showed solution‐phase circularly polarized luminescence (CPL) in the red region of the visible spectrum (λ_em(max) from 621 to 663 nm). The parent dipyrromethene is desymmetrised through O chelation of boron by the 3,5‐ortho‐phenolic substituents, inducing a helical chirality in the fluorophore. The combination of high luminescence dissymmetry factors (|g_lum| up to 4.7 ×10^?3) and fluorescence quantum yields (Φ_F up to 0.73) gave exceptionally efficient circularly polarized red emission from these simple small organic fluorophores, enabling future application in CPL‐based bioimaging.     

Circularly Polarized Luminescence from Simple Organic Molecules

This article aims to show the identity of “circularly polarized luminescent active simple organic molecules” as a new concept in organic chemistry due to the potential interest of these molecules, as availed by the exponentially growing number of research articles related to them. In particular, it describes and highlights the interest and difficulty in developing chiral simple (small and non‐aggregated) organic molecules able to emit left‐ or right‐circularly polarized light efficiently, the efforts realized up to now to reach this challenging objective, and the most significant milestones achieved to date. General guidelines for the preparation of these interesting molecules are also presented.     

手性有机光电功能材料及其圆偏振光发射与探测

手性有机半导体由于其新颖的性质引起了有机光电领域极大的研究兴趣. 将手性引入有机半导体材料不仅可以调控聚集态结构影响载流子输运进而影响光电器件的性能, 而且催生了圆偏振光直接发射与探测材料与器件的产生与发展. 手性材料与圆偏振光之间的相互作用使得其在3D显示、量子通讯、信息存储与处理等领域展示出广泛的应用前景. 本综述总结近年来手性有机光电材料及器件的研究进展, 主要围绕手性对有机半导体材料性质与器件性能的影响展开, 聚焦于手性有机半导体的圆偏振光直接发射与探测等研究, 旨在进一步为手性有机光电子领域的发展提供系统的认识.     

Discriminating Chiral Supramolecular Motions by Circularly Polarized Luminescence

Molecular motions are closely associated with the behaviors and properties of organic materials. However, monitoring molecular motions is challenging. Herein, a chiral supramolecular system consisting of L-/D-phenylalanine (LPF/DPF) as a chiral inducer and an achiral tetraphenylethene derivative (TPEF) as a molecular rotor has been proposed and explored for real-time discriminating the supramolecular motions by the visualization of circularly polarized luminescence (CPL) signal variations. Derived from the ordered molecular motions of TPEF induced by LPF/DPF, highly organized aggregates have been progressively assembled in a controlled manner with differentiated morphologies, including spherical particles, one-dimensional fibers, and floor-shaped supercrystals. Notably, increasing level of ordered aggregates, in turn, led to quenching emissions, while the CPL signals have been dramatically amplified accompanying by a sharp enhancement of luminescence dissymmetry factors (g_lum) from nearly 0 to −0.1. The significant amplification of CPL is attributed to the ordered aggregates of supramolecules, leading to the decrease of electric transition dipole moments in supramolecular system. As a result of the chiral supramolecular motions powered by supramolecular crystallization, the supramolecular motions are conveniently discriminated by visual CPL signal variation with an enhancement of g_lum value from 0 to −0.1 in real time.     

Oxidation of an Internal-Edge-Substituted [5]Helicene-Derived Phosphine Synchronously Enhances Circularly Polarized Luminescence

Small chiral organic molecules with CD properties are in high demanded due to their potential use in promising electronic and biological applications. Herein, we reveal a system in which the oxidation of a phosphino group to the corresponding phosphine oxide on the inner rim of a helicene derivative induces a CPL response. Laterally π-extended 7,8-dihydro[5]helicenes bearing phosphine and phosphine oxide groups on their inner helical rims (i. e., the C1 position) were synthesized, and their helical structures were unambiguously determined by X-ray crystallography. The photophysical (UV/visible and emission) and chiroptical properties of these compounds were investigated in various solvents. Despite their structural similarities, phosphine oxide showed a significantly better CPL response than phosphine, with a high dissymmetry factor for emission (|g_lum|=(1.3–1.9)×10⁻³) that can be attributed to structural changes in the interior of the helicene helix.     

Azahelicene‐Fused BODIPY Analogues Showing Circularly Polarized Luminescence

Helical carbazole‐based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene‐incorporated BF₂ dyes were elucidated by x‐ray diffraction analysis. DFT calculations revealed that the π‐conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene‐fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties.     

手性有机小分子圆偏振发光的研究进展

圆偏振发光不仅能直观地反映手性发光体系的激发态结构信息,而且在3D显示、自旋信息通讯、信息存储与处理、CPL激光、生物探针等领域具有广泛的应用前景.因此,近年来圆偏振发光材料引起了人们越来越多的兴趣与关注,成为有机发光功能材料领域一个新的研究热点.本综述总结近年来关于手性有机小分子圆偏振发光的研究进展,主要围绕具有中心手性、轴手性、面手性和螺旋手性的圆偏振发光有机小分子展开介绍.     

A Smart Sensing Method for Object Identification Using Circularly Polarized Luminescence from Coordination‐Driven Self‐Assembly

The potential use of circularly polarized luminescence for object identification in a sensor application is demonstrated. New luminescence probes using pyrene derivatives as sensor luminophores were developed. (R,R)‐Im₂Py and (S,S)‐Im₂Py contain two chiral imidazole moieties at 1,6‐positions through ethynyl spacers (angle between spacers ca. 180°). The probe molecules spontaneously self‐assemble into chiral stacks (P or M helicity) upon coordination to metal ions with tetrahedral coordination (Zn²⁺). The chiral probes display neither circular dichroism (CD) nor circularly polarized luminescence (CPL) without metal ions. However, (R,R)‐Im₂Py and (S,S)‐Im₂Py exhibit intense chiroptical activity (CD and CPL) upon self‐assembly with Zn²⁺ ions. (R,R)‐Im₂Py and (S,S)‐Im₂Py with chemical stimuli‐responsibility allow sensing using the CPL signal as detection output, enabling us to discriminate between a signal from the target analyte and that from non‐target species.     

Solid-State Near-Infrared Circularly Polarized Luminescence from Chiral YbIII-Single-Molecule Magnet

A field-induced chiral Yb^III Single-Molecule Magnet (SMM) displayed an unprecedented near-infrared circularly polarized luminescence (NIR-CPL) in the solid-state. The bridging bis(1,10-phenantro[5,6b])tetrathiafulvalene triad ( L ) allowed an efficient sensitization of the NIR ²F_5/2→²F_7/2 emission while the NIR-CPL is associated to the f-f transitions of the Yb^III ion bearing chiral β-diketonate derived-camphorate ancillary ligands.     

Dual Upconverted and Downconverted Circularly Polarized Luminescence in Donor–Acceptor Assemblies

Through mimicking both the chiral and energy transfer in an artificial self‐assembled system, not only was chiral transfer realized but also a dual upconverted and downconverted energy transfer system was created that emit circularly polarized luminescence. The individual chiral π‐gelator can self‐assemble into a nanofiber exhibiting supramolecular chirality and circularly polarized luminescence (CPL). In the presence of an achiral sensitizer Pd^II octaethylporphyrin derivative, both chirality transfer from chiral gelator to achiral sensitizer and triplet‐triplet energy transfer from excited sensitizer to chiral gelator could be realized. Upconverted CPL could be observed through a triplet–triplet annihilation photon upconversion (TTA‐UC), while downconverted CPL could be obtained from chirality‐transfer‐induced emission of the achiral sensitizer. The interplay between chiral energy acceptor and achiral sensitizer promoted the communication of chiral and excited energy information.     

Molecular Design,Circularly Polarized Luminescence,and Helical Self‐Assembly of Chiral Aggregation‐Induced Emission Molecules

Aggregation‐induced emission luminogens (AIEgens) are a new class of luminophors, which are non‐emissive in solution, but emit intensively upon aggregation. By properly designing the chemical structures of the AIEgens, their aggregation process can be tuned towards a desired direction to give diverse novel luminescent architectures of micelles, rods, and helical fibers. AIEgens represent a kind of promising building block for the fabrication of luminescent micro/nanostructures with controllable morphologies. In this review, we describe our recent work in this research area, focusing on the molecular design, circularly polarized luminescence properties, and helical self‐assembly behavior of AIEgens.     

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et₂AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the Φ_F and g_lum of up to 0.22 and −3.5×10⁻³, respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.     

Small Figure-Eight Luminophores: Double-Twisted Tethered Cyclic Binaphthyls Boost Circularly Polarized Luminescence

Double-twisted cyclic binaphthyls, in which two naphthalenes are tethered by -O(CH₂)_nO- linkage (n=1–3), have been synthesized. X-ray analyses and DFT calculations revealed a tightly constrained stereogenic figure-eight geometry. Tethering of two naphthalenes by short linkage forces a small dihedral angle, and the cyclic binaphthyls with short tether (n=1, 2) exhibit remarkable boosting of the g_lum value (1.0–1.6×10⁻²) in circularly polarized luminescence (CPL) and unusual g_lum/g_abs ratios (0.93–1.3). These experimental high |g_lum| values are in accord with the results of excited state TD-DFT calculations, which show transannular interactions and that consequent extensive delocalization occurs throughout the figure-eight π-core. As a result, the present figure-eight luminophore promote the elongation of the magnetic transition dipole moment that results in significant increases in g_lum values.