Circularly Polarized Phosphorescence Research Articles

Circularly Polarized Phosphorescence Properties of Binuclear Cyclometalated Platinum(II) Complexes Bearing Axially Chiral Schiff-Base Ligands.

The synthesis, structure, and circularly polarized phosphorescence (CPP) properties of axially chiral cyclometalated binuclear platinum(II) complexes were described. A series of optically pure binuclear platinum(II) complexes were synthesized in five steps from commercially available (R)- or (S)-1,1'-bi-2-naphthol (BINOL) as starting materials. Their three-dimensional molecular structures and square-planar coordination geometries were elucidated from X-ray diffraction and 2D NMR analysis. The complexes were found to exhibit red- to near-infrared photoluminescence in solution and in the solid state. Furthermore, dilute DMSO solutions of the enantiopure samples showed red CPP with relatively high luminescence dissymmetry factor (glum) values. Density functional theory (DFT) calculations were conducted to examine their three-dimensional molecular conformations and photophysical properties.

Tuning the circularly polarized phosphorescence of platinum(II) complexes through a chiral cation strategy.

Circularly polarized phosphorescent (CPP) materials, especially chiral platinum(II) complexes, which combine the advantages of both circularly polarized luminescence (CPL) and phosphorescence, show broad potential applications in chiral optoelectronic devices. Developing CPP emitters with both excellent chiroptical properties and high yield is urgently needed. Here, a chiral cation strategy is employed to construct the CPP Pt(II) complexes R/S-ABA·[Pt(ppy)Cl2] and R/S-MBA·[Pt(ppy)Cl2] through a simple one-step reaction with almost 100% yield. The circular dichroism and CPL spectra confirm that the chirality was successfully transferred to the [Pt(ppy)Cl2]- anion. The luminescence asymmetry factors (glum) are +1.4/-1.8 × 10-3 for R/S-ABA·[Pt(ppy)Cl2] and +4.4/-2.8 × 10-3 for R/S-MBA·[Pt(ppy)Cl2]. The stronger chiroptical property of R/S-MBA·[Pt(ppy)Cl2] is attributed to the enhanced chiral structural deformation and better matched electric and magnetic transition dipole moments. This chiral cation strategy is confirmed to efficiently construct CPP Pt(II) complexes, which will accelerate the development of CPP emitters towards commercialization.

Achieving Circularly Polarized Phosphorescence through Noncovalent Clipping of Metallotweezers.

Circularly polarized phosphorescent materials, based on host-guest complexation, have received significant attention due to their outstanding emission performance in solutions. Recent studies have primarily focused on macrocyclic host-guest complexes. To broaden the scope of this research, there is a keen pursuit of developing novel chiral phosphorescent host-guest systems. Metallotweezers with square-planar d8 transition metal complexes emerge as promising candidates for achieving this objective. Specifically, metallotweezers, comprising platinum(II) terpyridine and gold(III) diphenylpyridine pincers on a diphenylpyridine scaffold, have been designed and synthesized. Due to the preorganization effect rendered by the diphenylpyridine scaffold, the resulting metallotweezers are capable of complexing with each other and forming quadruple stacking structures. The phosphorescent emission is enhanced owing to the synergistic rigidifying and shielding effects. Meanwhile, the steric effect of chiral (1R) pinene units on the platinum(II) terpyridine pincers results in a stereospecific twist for the quadruple stacking structures. Thus, the chirality transfers from the molecular to the supramolecular level. By a combination of phosphorescent enhancement and supramolecular chirality for the clipping complex, circularly polarized phosphorescent emission is achieved. Overall, noncovalent clipping of metallotweezers exemplified in the current study presents a novel and effective approach toward solution-processable circularly polarized phosphorescent materials.

Chiral Ligand-Concentration Mediating Asymmetric Transformations of Silver Nanoclusters: NIR-II Circularly Polarized Phosphorescence Lighting.

Near infrared (NIR) emitter with circularly polarized phosphorescence (CPP), known as NIR CPP, has emerged as a key part in the research of cutting-edge luminescent materials. However, it remains a challenge to obtain nanoclusters with NIR CPP activity. Here, we propose an asymmetric transformation approach to efficiently synthesize two pairs of chiral silver nanoclusters (R/S-Ag29 and R/S-Ag16) using an achiral Ag10 nanocluster as starting material in the presence of different concentration chiral inducer (R/S)-1,1'-binaphthyl-2,2'-diyl hydrogenphosphate (R/S-BNP). R/S-Ag29, formed in the low-concentration R/S-BNP, exhibits a unique kernel-shell structure consisting of a distorted Ag13 icosahedron and an integrated cage-like organometallic shell with a C3 symmetry, and possesses a superatomic 6-electron configuration (1S2|1P4). By contrast, R/S-Ag16, formed in the high-concentration R/S-BNP, features a sandwich-like pentagram with AgI-pure kernel. Profiting from the hierarchically chiral structures and superatomic kernel-dominated phosphorescence, R/S-Ag29 exhibits infrequent CPP activity in the second near-infrared (975 nm) region, being the first instance of NIR-II CPP observed among CPL-active metal nanoclusters. This study presents a new approach to reduce the difficulty of de novo synthesis for chiral silver nanomaterials, and facilitates the design of CPP-active superatomic nanoclusters in NIR region.

Chiral Ligand‐Concentration Mediating Asymmetric Transformations of Silver Nanoclusters: NIR‐II Circularly Polarized Phosphorescence Lighting

AbstractNear infrared (NIR) emitter with circularly polarized phosphorescence (CPP), known as NIR CPP, has emerged as a key part in the research of cutting‐edge luminescent materials. However, it remains a challenge to obtain nanoclusters with NIR CPP activity. Here, we propose an asymmetric transformation approach to efficiently synthesize two pairs of chiral silver nanoclusters (R/S‐Ag29 and R/S‐Ag16) using an achiral Ag10 nanocluster as starting material in the presence of different concentration chiral inducer (R/S)‐1,1′‐binaphthyl‐2,2′‐diyl hydrogenphosphate (R/S‐BNP). R/S‐Ag29, formed in the low‐concentration R/S‐BNP, exhibits a unique kernel‐shell structure consisting of a distorted Ag13 icosahedron and an integrated cage‐like organometallic shell with a C3 symmetry, and possesses a superatomic 6‐electron configuration (1S2|1P4). By contrast, R/S‐Ag16, formed in the high‐concentration R/S‐BNP, features a sandwich‐like pentagram with AgI‐pure kernel. Profiting from the hierarchically chiral structures and superatomic kernel‐dominated phosphorescence, R/S‐Ag29 exhibits infrequent CPP activity in the second near‐infrared (975 nm) region, being the first instance of NIR‐II CPP observed among CPL‐active metal nanoclusters. This study presents a new approach to reduce the difficulty of de novo synthesis for chiral silver nanomaterials, and facilitates the design of CPP‐active superatomic nanoclusters in NIR region.

Enantiopure [6]-Azairidahelicene by Dynamic Kinetic Resolution of a Configurationally Labile [4]-Helicene.

A pair of enantiopure [6]-azairidahelicenes incorporating chirality at the metal center and on the helicenic ligand were synthesized by dynamic kinetic resolution (dkr) of a configurationally labile [4]-helicenic ligand (4-(2-pyridyl)-benzo[g]phenanthrene, L1H) using bis-cyclometalated chiral-at-metal only iridium(III) precursors as chiral inductors. The origin of the observed dkr is attributed to the different conformation and stability of diastereomeric reaction intermediates formed during the cyclometalation process. The isolated enantiomers exhibited circularly polarized phosphorescence (CPP), with |gphos| values of 1.8×10-3.

Enantiopure [6]‐Azairidahelicene by Dynamic Kinetic Resolution of a Configurationally Labile [4]‐Helicene

AbstractA pair of enantiopure [6]‐azairidahelicenes incorporating chirality at the metal center and on the helicenic ligand were synthesized by dynamic kinetic resolution (dkr) of a configurationally labile [4]‐helicenic ligand (4‐(2‐pyridyl)‐benzo[g]phenanthrene, L1H) using bis‐cyclometalated chiral‐at‐metal only iridium(III) precursors as chiral inductors. The origin of the observed dkr is attributed to the different conformation and stability of diastereomeric reaction intermediates formed during the cyclometalation process. The isolated enantiomers exhibited circularly polarized phosphorescence (CPP), with |gphos| values of 1.8×10−3.

Chiral Coordination Assembly-Induced Phosphorescent Frameworks for Circularly Polarized Phosphorescence

Chiral Coordination Assembly-Induced Phosphorescent Frameworks for Circularly Polarized Phosphorescence

Boost the Circularly Polarized Phosphorescence of Chiral Organometallic Platinum Complexes by Hierarchical Assembly into Fibrillar Networks.

Circularly polarized luminescence (CPL)-active molecular materials have drawn increasing attention due to their promising applications for next-generation display and optoelectronic technologies. Currently, it is challenging to obtain CPL materials with both large luminescence dissymmetry factor (glum) and high quantum yield (Φ). A pair of enantiomeric N N C-type Pt(II) complexes (L/D)-1 modified with chiral Leucine methyl ester are presented herein. Though the solutions of these complexes are CPL-inactive, the spin-coated thin films of (L/D)-1 exhibit giantly-amplified circularly polarized phosphorescences with |glum| of 0.53 at 560 nm and Φair of ~50 %, as well as appealing circular dichroism (CD) signals with the maximum absorption dissymmetry factor |gabs| of 0.37-0.43 at 480 nm. This superior CPL performance benefits from the hierarchical formation of crystalline fibrillar networks upon spin coating. Comparative studies of another pair of chiral Pt(II) complexes (L/D)-2 with a symmetric N C N coordination mode suggest that the asymmetric N N C coordination of (L/D)-1 are favorable for the efficient exciton delocalization to amplify the CPL performance. Optical applications of the thin films of (L/D)-1 in CPL-contrast imaging and inducing CP light generation from achiral emitters and common light-emitting diode lamps have been successfully realized.

Boost the Circularly Polarized Phosphorescence of Chiral Organometallic Platinum Complexes by Hierarchical Assembly into Fibrillar Networks

AbstractCircularly polarized luminescence (CPL)‐active molecular materials have drawn increasing attention due to their promising applications for next‐generation display and optoelectronic technologies. Currently, it is challenging to obtain CPL materials with both large luminescence dissymmetry factor (glum) and high quantum yield (Φ). A pair of enantiomeric N N C‐type Pt(II) complexes (L/D)‐1 modified with chiral Leucine methyl ester are presented herein. Though the solutions of these complexes are CPL‐inactive, the spin‐coated thin films of (L/D)‐1 exhibit giantly‐amplified circularly polarized phosphorescences with |glum| of 0.53 at 560 nm and Φair of ~50 %, as well as appealing circular dichroism (CD) signals with the maximum absorption dissymmetry factor |gabs| of 0.37–0.43 at 480 nm. This superior CPL performance benefits from the hierarchical formation of crystalline fibrillar networks upon spin coating. Comparative studies of another pair of chiral Pt(II) complexes (L/D)‐2 with a symmetric N C N coordination mode suggest that the asymmetric N N C coordination of (L/D)‐1 are favorable for the efficient exciton delocalization to amplify the CPL performance. Optical applications of the thin films of (L/D)‐1 in CPL‐contrast imaging and inducing CP light generation from achiral emitters and common light‐emitting diode lamps have been successfully realized.

Directed Chiral Self‐Assembly of Purely Organic Phosphors for Room‐Temperature Circularly Polarized Phosphorescence

AbstractCircularly polarized phosphorescence (CPP) is increasingly recognized in materials science for its unique applications in optoelectronic devices, chiral recognition, and bioimaging. This study underscores a novel directed chiral self‐assembly strategy of purely organic phosphors into supramolecular nanostructures to achieve bright room‐temperature circularly polarized phosphorescence (RT‐CPP). RT‐CPP molecules are built on an aromatic carbonyl structure having also Br to mix (n,π*) and (π,π*) characters and to enable the heavy atom effect. Side chains are rationally designed to have strong hydrogen bonding, van der Waals interactions, and a chiral center for directed chiral self‐assembly into supramolecular nanostructures. The tightly packed resulting supramolecular nanostructures also impower efficient suppression of molecular motions, thereby minimizing non‐radiative decay and facilitating bright CPP emission at room temperature. The developed self‐assembled supramolecular structures exhibit RT‐CPP with the dissymmetry factor (glum) of ≈10−3, a high phosphorescence quantum yield of 4.1%, and a rapid triplet decay time of 180 microseconds. The presented molecular design principle enabling RT‐CPP from purely organic phosphors may pave the way for novel photonic materials.

Strong Circularly Polarized Phosphorescence of Achiral Pt(II) Metallomesogen Induced by Using a Chiral Co‐Assembly Strategy

AbstractThe high planarity and heavy‐atom effect of Pt(II) metallomesogens promote their stacking in the aggregated state and highly efficient phosphorescence. This makes them promising candidate materials for circularly polarized phosphorescence (CPP) triggered by using a chiral co‐assembly strategy. In this paper, a nematic phase, achiral robot‐like Pt(II) metallomesogen (TFPt) is synthesized, which combines two anchored chiral binaphthyl inducers (R/S1 or R/S2) to construct cholesteric liquid crystal (N*‐LC) co‐assemblies (R/S1)n‐(TFPt)1‐n and (R/S2)n‐(TFPt)1‐n via intermolecular interactions. The resultant N*‐LC chiral co‐assemblies (R1)0.03‐(TFPt)0.97 and (R2)0.03‐(TFPt)0.97 exhibit the strongest CPP emission with high dissymmetry factors (gem) of up to 0.18 and 0.27, respectively, stemming from the formation of regular helical nanofibers on spin‐coated films via co‐assembly process after thermal annealing at 165 °C.

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.

Kinetically Controlled Structural Modulation of the Self-Assembled Silver Nanoclusters.

Metal nanoclusters (NCs) with atomic precision are growing into a fascinating class of building blocks for supramolecular chemistry. What makes it more interesting is the enhanced optical properties of the ordered structures, including aggregation-induced emission (AIE). However, algorithm dictating the self-assembly of metal NCs in multicomponent environment remains largely unknown, and effective means to manipulate the self-assembly is still lacking, especially under kinetic control. Herein, nanofibers which contain sub-1nm nanowires and exhibit circularly polarized phosphorescence (CPP) are obtained from crystallization-induced self-assembly (CISA) of water-soluble, negatively charged silver NCs (Ag9 -NCs) in the presence of glutamic acid (Glu). By the introduction of a positively-charged additive (choline chloride, CC), the structure of the nanowires is modulated and the lateral interaction between adjacent nanofibers is adjusted, leading to simultaneous improvement of the phosphorescence and chirality which finally enhances CPP. Importantly, changing the time at which CC is introduced altered the kinetic pathway of the CISA, which enables to effectively manipulate both the final structures of the self-assembled Ag9 -NCs and the output of the optical signals.

Enhancing Circularly Polarized Phosphorescence via Integrated Top‐Down and Bottom‐Up Approach

AbstractIn the dynamic domain of chiroptical technologies, it is imperative to engineer emitters endowed with circularly polarized luminescence (CPL) properties. This research demonstrates an advancement by employing a combined top‐down and bottom‐up strategy for the simultaneous amplification of photoluminescence quantum yield (Φ) and the luminescence dissymmetry factor (glum). Square‐planar Pt(II) complexes form helical assemblies, driven by torsional strain induced by bis(nonyl) chains. Integration of chiral anions leads these assemblies to prefer distinct helical sense. This arrangement activates the metal‐metal‐to‐ligand charge transfer (MMLCT) transition that is CPL‐active, with Φ and |glum| observing an upswing contingent on the charge number and aryl substituents in chiral anions. Utilizing the soft‐lithographic micromolding in capillaries technique, we could fabricate exquisitely‐ordered, one‐dimensional co‐assemblies to achieve the metrics to Φ of 0.32 and |glum| of 0.13. Finally, our spectroscopic research elucidates the underlying mechanism for the dual amplification, making a significant stride in the advancement of CPL‐active emitters.

Liquid Based Circularly Polarized Phosphorescence of a Chiral Schiff Base Platinum(II) Complex Bearing Polyethylene Glycol Chains

AbstractA chiral Schiff base platinum(II) complex1bearing polyethylene glycol (PEG) chains was synthesized. The complex was found to melt at 44 °C whereas its non‐substituted analogue2has a high melting point (>300 °C). Upon cooling after melting, the complex remained liquid at room temperature over 30 minutes and exhibited yellow phosphorescence. Circularly polarized phosphorescence (CPP) properties were examined and it was found that the absolute value of the luminescence dissymmetry factor (glum) increases significantly in the liquid state compared to the dilute solution state. Herein, we report the first example of CPP from solvent‐free supercooled liquids.

Frontiers in Circularly Polarized Phosphorescent Materials

AbstractCircularly polarized luminescence (CPL) materials have received increasing attention in recent years. Amongst various CPL materials, circularly polarized phosphorescence (CPP) materials featuring long life‐time represent a novel research frontier and exhibit promising applications in various fields. Herein, the state‐of‐the‐art advances of CPP materials are systematically summarized, as classified into transition metal complexes, organic small molecules, polymers, and organic/inorganic hybrid materials. Besides, the recent applications of CPP materials in organic light‐emitting diodes and encryption display are also summarized. Furthermore, the current challenges and future perspectives are put forward. It is expected that this review will offer more inspirations for the future rational design of advanced CPP materials, thus further promoting their future practical applications.

Helical Induction, Chiroptical Properties, and Quantitative Prediction of the Dissymmetry Factor on the Circularly Polarized Phosphorescence of Iminopyrrolyl Platinum(II) Complexes

Chiral transition metal complexes have attracted significant attention for the development of optoelectrical materials, such as circularly polarized phosphorescence (CPP)-emitting devices. In this paper, we report the helicity induction of d-π-conjugated platinum(II) complexes by the point chirality on 1,2-diaminocyclohexane and their CPP properties. The obtained C2-helical complexes exhibited excellent chiroptical properties with high dissymmetry factors (circular dichroism: gabs = 1.2 × 10–2, CPP: gphos = 3.2 × 10–3). Moreover, we conducted a theoretical investigation of the dissymmetry factor of CPP, gphos,calc, using a kinetic model of triplet state sublevels. The ab initio calculations represented the experimental gphos values, as well as the impact of helical chirality on the CPP.

Circularly Polarized Phosphorescence from Cocrystallization of Atomic Precise Silver Nanoclusters with Tartaric Acid

AbstractRecently, advanced optical materials with circularly polarized phosphorescence (CPP) have attracted much attention. However, such materials are limited due to the difficulty of preparation and the scarcity of precursors. Herein, CPP materials are constructed for the first time using water‐soluble, pseudo‐chiral silver nanoclusters with atomic precision ((NH4)9 [Ag9 (mba)9], H2mba = 2‐mercaptobenzoic acid, abbreviated to Ag9‐NCs hereafter). Induced by the complexation of l‐ or d‐tartaric acid (TrA) through hydrogen bonding, Ag9‐NCs crystallize from aqueous solutions, during which the chirality of the hybrid is amplified and the phosphorescence of Ag9‐NCs is enhanced. It is speculated that the chiral transfer from TrA to Ag9‐NCs is the main source of the well‐defined circular dichroism signals with good repeatability. The Ag9‐NCs/TrA cocrystals exhibit good CPP performance with dissymmetric factors up to 1.05 × 10−2, which is the highest value for metal NCs‐based CPP materials. This work is expected to be an inspiration for preparing metal NCs‐based CPP materials by supramolecular strategy. The so‐obtained organic–inorganic CPP materials can find a variety of applications in optoelectronic devices.

Ruthenium Complexes Bearing Axially Chiral Bipyridyls: The Mismatched Diastereomer Showed Red Circularly Polarized Phosphorescence.

RutheniumII complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ-(S)- and Λ-(S)-diastereomers were obtained. The X-ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ-(S)- and Λ-(S)-isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ-(S)-isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ-(S)-isomer, the six cumulative CH/π interactions suppress further distortion in the T1 state.