Luminescent Molecules Research Articles

Chiral‐at‐Cage Carboranes for Circularly Polarized Luminescence and Aggregation‐Induced Electrochemiluminescence

AbstractHerein, we report the structures of chiral‐at‐cage carborane derivatives bearing carbazole chromophores that emit circularly polarized luminescence (CPL) and aggregation‐induced electrochemiluminescence (AIECL). By adjusting the substituent positions on the carborane derivatives, two chiral luminescent molecules, Cb1 and Cb2, with different properties were obtained. The photoluminescence dissymmetry factors |gPL| of both (R/S)‐Cb1 and (R/S)‐Cb2 enantiomers in neat films were as high as 6.24×10−3 and 7.38×10−3, respectively. Cb1 showed a deep blue emission peak at 434 nm in n‐pentane. Interestingly, distinct fluorescence and CPL spectra were observed in solvents of different polarities due to the twisted intramolecular charge transfer effect, suggesting its potential use in solvent recognition. Meanwhile, Cb2 exhibited good AIECL property, excellent ECL stability and could be used for determining dopamine concentrations, suggesting its potential applications in biology and diagnosis.

Chiral-at-Cage Carboranes for Circularly Polarized Luminescence and Aggregation-Induced Electrochemiluminescence.

Herein, we report the structures of chiral-at-cage carborane derivatives bearing carbazole chromophores that emit circularly polarized luminescence (CPL) and aggregation-induced electrochemiluminescence (AIECL). By adjusting the substituent positions on the carborane derivatives, two chiral luminescent molecules, Cb1 and Cb2, with different properties were obtained. The photoluminescence dissymmetry factors |gPL | of both (R/S)-Cb1 and (R/S)-Cb2 enantiomers in neat films were as high as 6.24×10-3 and 7.38×10-3 , respectively. Cb1 showed a deep blue emission peak at 434 nm in n-pentane. Interestingly, distinct fluorescence and CPL spectra were observed in solvents of different polarities due to the twisted intramolecular charge transfer effect, suggesting its potential use in solvent recognition. Meanwhile, Cb2 exhibited good AIECL property, excellent ECL stability and could be used for determining dopamine concentrations, suggesting its potential applications in biology and diagnosis.

Luminescent push-pull triphenylamine-based molecules end-capped with various electron-withdrawing groups: Synthesis and properties

Organic luminescent materials are widely used in various electronic and optoelectronic devices upon growing demands of science and technology. Enhancement of spectral-luminescence characteristics for such materials and in depth understanding of “structure-property” relationships remain challenging tasks. Herein, we report on synthesis and comprehensive investigation of the series of novel luminescent push-pull molecules with triphenylamine unit as an electron donor block and thiophene as a π-spacer, which end-capped with various types of electron-withdrawing groups (EWGs), which are commonly used for the molecular design of various functional materials in organic electronics. The results allowed us to evaluate the impact of EWG type used on the target materials characteristics. Phenyl-substituted EWGs were found to be more suitable for the design of highly thermally and electrochemically stable materials with relatively high melting temperatures and melting enthalpies. Depending on the EWG nature luminescence maxima of the luminophores demonstrated significant variability, e.g. from 509 nm to 750 nm, while the photoluminescence quantum yield (PLQY) values laid in the range of 1–89%. All luminophores showed good compatibility with a polystyrene (PS) matrix, in which PLQYs were generally higher (up to 25-fold enhancement) compared to the corresponding solutions or polycrystalline films. The changes of spectral characteristics observed for these luminophores were well described using basic relations of the semi-empirical theory of solvatochromism. Based on lifetime of excited states measurements, it was shown that the excited state non-radiative deactivation constants values the major contributors to PLQY values in THF solutions, while increase of the PLQY values in PS films can be associated with decrease of the probability of non-radiative deactivation of the excited states.

Photocyclization‐Induced Emission Enhancement and Circularly Polarized Luminescence Inversion of Achiral Emitters in Co‐Assembled Gels

Precisely controlling the circularly polarized emission of achiral organic luminescent molecules in an aggregated state is a remaining challenge in this research field, since it should simultaneously overcome the ubiquitous issues of chirality transfer and aggregation‐caused quenching occurring in the aggregated systems. Herein, a facile and universal approach to achieving assembly‐accelerated photocyclization and photocyclization‐enhanced emission of tetraphenylethylene (TPE) derivative in the gel state is reported. This experimental data reveal that the co‐assembled gels exhibit high efficiency of photocyclization (≥100 times more efficient than the TPE‐based derivative in solution) via the hydrogen‐bonding‐driven helical assembly, displaying sharply enhanced emission (with the maximum enhancement of 105 times) after the photocyclization and oxidation under ultraviolet irradiation. Furthermore, inverted circularly polarized luminescence (CPL) is achieved after the photocyclization of TPE‐based gels. The strategy of assembly‐enhanced emission and photomodulated CPL inversion of fluorescent organic systems in the aggregated state can increase the abundance of chiral luminescent soft matters, leading to versatile applications in organic chiroptical optoelectronics and smart flexible displaying devices.

Boosting Blue Emission of Organic Cations in a Sn(IV)-Based Perovskite by Constructing Intermolecular Interactions.

Improving the photoluminescence (PL) efficiency of organic luminescent molecules is still a great challenge. Herein, a novel zero-dimensional Sn(IV)-based halide (C9H8N)2SnCl6 is prepared by assembling inactive quinoline cations and stable [SnCl6]2- polyhedra. Experimental characterizations and theoretical calculations show that the blue emission of (C9H8N)2SnCl6 centered at 433 nm is derived from the organic cations. Surprisingly, the PL efficiency of the as-prepared halide is nearly 50 times higher than that of the organic precursor and exhibits ultrahigh stability. Structural analysis shows that the introduction of inorganic clusters regulates the stacking mode of organic components and forms hydrogen bonds. This strong intermolecular interaction enhances the structural rigidity of (C9H8N)2SnCl6, inhibits concentration quenching and vibrational dissipation, and thus significantly improves the PL efficiency and stability of the organic cations. This work provides an important way to improve the PL performance and stability of organic species by constructing efficient intermolecular interactions.

Development of Yellow-to-Orange Photoluminescence Molecules Based on Alterations in the Donor Units of Fluorinated Tolanes.

Since the aggregation-induced emission (AIE) phenomenon was first reported by Tang et al., much effort has been devoted to the development of solid-state luminescent molecules by chemists worldwide. Our group successfully developed fluorinated tolanes as novel compact π-conjugated luminophores with blue photoluminescence (PL) in the crystalline state. Moreover, we reported the yellow-green PL molecules based on their electron-density distributions. In the present study, we designed and synthesized fluorinated tolanes with various amine-based donors and evaluated their photophysical properties. The carbazole-substituted fluorinated tolane exhibited strong PL in the solution state, whereas piperidine- or phenothiazine-substituted fluorinated tolanes showed a dramatic decrease in PL efficiency. Notably, fluorinated tolanes with piperidine or phenothiazine substituents displayed yellow-to-orange PL in the crystalline state; this may have occurred because these tolanes exhibited tightly packed structures formed by intermolecular interactions, such as H···F hydrogen bonds, which suppressed the non-radiative deactivation process. Moreover, fluorinated tolanes with amine-based donors exhibited AIE characteristics. We believe that these yellow-to-orange solid PL molecules can contribute to the development of new solid luminescent materials.

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Handheld device for on-site sensitive detection of genetically modified crop based on supramolecular fluorescence material

Herein, a handheld device for on-site detection of genetically modified crop was developed. To meet the requirement of highly sensitive detection, single-wavelength light emitting diode was used as excitation light source, silicon photodiode with a dark current of pA level was adopted for photoelectric conversion, and phase-sensitive signal acquisition and amplification were carried out to improve the signal-to-noise ratio. Specially, micron-scale supramolecular fluorescence material was proposed for the first time as the signal label of sandwich immunoassay, which is a luminescent molecule aggregate. It could bring much greater increment in fluorescence intensity by increasing the number of luminescent molecules and accelerating the internal energy recombination, resulting in an excellent detection sensitivity. Under optimal experimental conditions, genetically modified protein PAT/bar as a template could be detected in the range of 0.01 ~ 10,000 ng/mL, with a limit of quantification10 pg/mL. Selectivity, stability, precision and accuracy were all satisfied. And, real GM rice sample could be successfully detected, implying that this high-sensitivity on-site detection platform has broad application prospects in food inspection.

Flower-like Gold Nanoparticles for In Situ Tailoring Luminescent Molecules for Synergistic Enhanced Chemiluminescence.

In recent years, gold nanoparticles (AuNPs) have attracted much attention due to their ease of surface modification, excellent biocompatibility, and extraordinary optoelectronic and catalytic activities. Herein, based on a AuNP-catalyzed reaction, a strategy for tailoring luminescent molecules in situ is proposed to trigger an ultrastrong chemiluminescence (CL). In the strategy, flower-like AuNPs are prepared using CL molecular probes (Probe-OH for NaClO/ONOO-) via one-pot synthesis and subsequently act as a tailor for Probe-OH to generate novel CL molecules, allowing a synergistic CL enhancement about 4 times that of initial Probe-OH. Furthermore, by modification with poly(vinylpyrrolidone) (PVP) on the surface, the CL signals (only for NaClO) are amplified by 100 times based on an intermolecular chemically initiated electron exchange luminescence (CIEEL) mechanism. Given the improved sensitivity and selectivity over Probe-OH, the thus-formed CIEEL nanoplatform (PVP-Au) is successfully developed for detecting NaClO in a wide range of 2.5-100 μM, and the detection limit is 10.68 nM. This work provides unprecedented perspectives for expanding this facile and effective strategy for CL amplification based on AuNP catalysis.

Luminescent Behavior of Liquid–Crystalline Gold(I) Complexes Bearing a Carbazole Moiety: Effects of Substituent Bulkiness

Organometallic materials that exhibit white luminescence in condensed phases are of considerable interest for lighting and display applications. Herein, new carbazole-based Au(I) complexes containing an isocyanide group and a long pentyl chain were synthesized. The complex with an unsubstituted carbazole moiety exhibited a white emission at room temperature as well as nematic liquid crystalline behavior. Color tunability from white to blue was achieved when bulkier substituents were introduced at the 3 and 6 positions of the carbazole moiety. Furthermore, all complexes possessed long phosphorescence lifetimes in the crystal state. The proposed design framework provides new opportunities for practical applications using luminescent organometallic molecules.

Uncovering the Use of Fucoxanthin and Phycobiliproteins into Solid Matrices to Increase Their Emission Quantum Yield and Photostability

In the search for a better and brighter future, the use of natural luminescent renewable materials as substitutes for synthetic ones in the energy field is of prime importance. The incorporation of natural pigments (e.g., xanthophylls and phycobiliproteins) is a fundamental step in a broad spectrum of applications that are presently marred by their limited stability. The incorporation of bio-based luminescent molecules into solid matrices allows the fabrication of thin films, which may dramatically increase the range of applications, including sustainable photovoltaic systems, such as luminescent solar concentrators or downshifting layers. In this work, we incorporated R-phycoerythrin (R-PE), C-phycocyanin (C-PC), and fucoxanthin (FX) into poly(vinyl alcohol) (PVA) and studied their optical properties. It was found that the emission and excitation spectra of the phycobiliproteins and FX were not modified by incorporation into the PVA matrix. Moreover, in the case of FX, the emission quantum yield (η) values also remained unaltered after incorporation, showing the suitability of the PVA as a host matrix. A preliminary photostability study was performed by exposing the solid samples to continuous AM1.5G solar radiation, which evidenced the potential of these materials for future photovoltaics.

Copper‐Promoted Direct Decarboxylative C3‐Acylation of Electron‐Rich Indolizines Using α‐Keto Acids

AbstractC‐3 substituted indolizines are important biological heterocycles and luminescent molecules. The development of new methods for direct arylation of indolizines is highly desired. Herein, the C3‐acylation of electron‐rich indolizines with α‐keto acids through Cu‐promoted decarboxylation was descried. Under this simple reaction conditions, a variety of indolizine derivatives were synthesized and characterized. The structure of product 3 a was confirmed in an X‐ray crystal analysis. In addition, the mechanism was also proposed.

Influence of Wallach’s Rule on Chiral AIE Systems and Its Application in Cryptographic Information Storage

Influence of Wallach’s Rule on Chiral AIE Systems and Its Application in Cryptographic Information Storage

Highly specific and selective fluorescent chemosensor for sensing of Hg(II) by NH-pyrazolate-functionalized AIEgens

Luminescent organic molecules are of important realistic significance to the human health and ecological environment due to their fascinating applications. Here we report the design and synthesis of luminescent organic-molecules by introducing two or four NH-pyrazolate groups as mercury-binding moieties to aromatic cores. Interestingly, the new aromatic tetraphenylene-bridged multi–NH–pyrazoles exhibit strong fluorescence in both aggregate and solid state and constitutes highly selective proof-of-concept luminescent sensor for Hg(II) ion among various competitive transition-metal ions in both organic and mixed solutions via metal-nitrogen binding. Especially, the present sensor including two NH-pyrazolyl groups showed an extremely high sensitivity with low limit of detection of 7.26 and 3.67 nM. The proposed design strategy provides a wide scope for the construction of unique turn-on sensors with substantial potential in the sense of heavy metal pollution in enviromental water samples.

Nickel-Catalyzed Synthesis of an Aryl Nitrile via Aryl Exchange between an Aromatic Amide and a Simple Nitrile

Herein, a nickel-catalyzed synthesis of an aryl nitrile via aryl exchange between an aromatic amide and a simple nitrile was developed. By using cheap, easy-to-handle, and low-toxic 4-cyanopyridine as the cyanating source, cyanation of various aromatic amides afforded an assortment of aryl nitriles including bioactive drugs and organic luminescent molecules in good yields. The reaction exhibited wide substrate scope, good functional group tolerance, and unique selectivity that were complementary to traditional methods. Moreover, two key nickel complexes formed by oxidative addition to each substrate are obtained and determined by X-ray crystallography, which gave strong support for the mechanism elucidations.

Theoretical perspective of relationship between molecular structure and luminescence properties for circularly polarized thermally activated delayed fluorescence

Circularly polarized luminescence (CPL) molecules with thermally activated delayed fluorescence (TADF) features show promising applications in high-efficiency circularly polarized organic light emitting diodes (CP-OLEDs). Herein, a pair of chiral molecules (R)-ImNT and (S)-ImNT are studied, two kinds of conformations are found by molecular dynamic conformation search, namely the quasi-axial and the quasi-equatorial conformations. Moreover, molecule with quasi-axial conformation is conducive to achieve outstanding CPL properties due to the large contributions of chiral groups to natural transition orbitals. While the energy gaps for quasi-equatorial conformations are significantly reduced and spin–orbit coupling effects between them are obviously increased. In addition, the quasi-equatorial configuration can facilitate the reverse intersystem crossing process to achieve remarkable TADF feature. Relationships between molecular geometries and CPL as well as TADF properties are revealed. Our research elucidates the relationship between geometric structure and luminescence mechanism, which could provide valuable insights for the design of efficient CPL-TADF emitters.

A signal amplification of near-infrared electrochemiluminescence immunosensor for SFTSV determination based on SiO2 photonic crystals nanomembrane

In this work, a novel near-infrared electrochemiluminescence signal amplification strategy was fabricated based on SiO2 photonic crystals nanomembrane as the ECL electrodes for sensitive and specific detection of SFTSV. The photonic crystal structure of the SiO2 nanomembrane has an excellent light scattering effect, which significantly increases the photon flux in the luminescent molecule and improves the excitation of the ECL molecule (CdTe@CdS QDs) by the re-radiation dipole electromagnetic field. In addition, the increase of the effective electroactive area of the photonic crystals modified electrode also prominently contributes to the ECL intensity. The results manifested that the SiO2 photonic crystals nanomembrane modified electrode constructed in this work can effectively improve the ECL intensity by about 7 times. Subsequently, a sandwich-type SFTSV immunosensor with a very low limit of detection of 0.0014 fg/mL was constructed. Due to the low cost and easy preparation of SiO2 photonic crystal solid-state electrodes, this work can not only effectively detect the SFTSV virus, but also provides an effective ECL signal amplification strategy.

Circularly polarised luminescence laser scanning confocal microscopy to study live cell chiral molecular interactions

The molecular machinery of life is founded on chiral building blocks, but no experimental technique is currently available to distinguish or monitor chiral systems in live cell bio-imaging studies. Luminescent chiral molecules encode a unique optical fingerprint within emitted circularly polarized light (CPL) carrying information about the molecular environment, conformation, and binding state. Here, we present a CPL Laser Scanning Confocal Microscope (CPL-LSCM) capable of simultaneous chiroptical contrast based live-cell imaging of endogenous and engineered CPL-active cellular probes. Further, we demonstrate that CPL-active probes can be activated using two-photon excitation, with complete CPL spectrum recovery. The combination of these two milestone results empowers the multidisciplinary imaging community, allowing the study of chiral interactions on a sub-cellular level in a new (chiral) light.

Aggregation-induced delayed fluorescence molecules with mechanochromic behaviors for efficient blue organic light-emitting diodes

Aggregation-induced delayed fluorescence (AIDF) materials combining the advantages of aggregation-induced emission and thermally activated delayed fluorescence have attracted considerable attention. However, blue AIDF materials with satisfactory electroluminescence efficiencies are still few. In this work, two blue luminescent molecules (XT-DPDBA and XT-BDPDBA) with evident AIDF characteristics and high photoluminescence quantum yields are developed by using rigid electron acceptor xanthenone and weak electron donor 10-dihydrodibenzo[b,e][1,4]azasiline. Both molecules exhibit prominent mechanochromic luminescence (MCL) behaviors originating from conformational interconversion between quasi-axial and quasi-equatorial conformations. The quasi-equatorial conformation has small singlet–triplet energy splitting and thus delayed fluorescence characteristic. Efficient blue organic light-emitting diodes are fabricated based on both molecules, providing high external quantum efficiencies of up to 27% and small efficiency roll-offs. These blue AIDF molecules with MCL property have good application potentials in various optical and electronic devices.

Structure of Self-assembled Peptide Determines the Activity of Aggregation-Induced Emission Luminogen-Peptide Conjugate for Detecting Alkaline Phosphatase.

The unique property of turning on their fluorescence after aggregation or assembly makes aggregation-induced emission luminogens (AIEgens) ideal luminescent molecules for the construction of self-assembled peptide-based nanoprobes. However, the characteristic highly twisted or propeller-shaped molecular conformation of AIEgens tends to prevent the assembly of AIEgen-peptides. Here, we show that (i) the distance between tetraphenylethene (TPE) and assembled peptides should not be too far (less than five glycines), otherwise the self-assembly of peptides cannot limit the intramolecular rotation of conjugated TPE and the luminous efficiency of TPE-peptide to alkaline phosphatase (ALP) will decrease; (ii) properly increasing the number of amino acids with self-assembly ability (three phenylalanines) can improve their ALP-responsive self-assembly and luminescence ability; (iii) the strategy of co-assembly with a non-AIEgen-capped self-assembled peptide is a simple and effective way to realize the efficient assembly and luminescence of AIEgen-peptides; and (iv) the hydrophilic and hydrophobic balance of the probe should always be considered in the construction of an efficient AIEgen-peptide probe. In addition, AIEgen-peptide probes show good selectivity and sensitivity for ALP detection both in vitro and in live bacteria. These insights illustrated here are crucial for guiding the design of AIEgen-conjugated supramolecular materials, especially for the construction of AIEgen-peptides, for enzymes detection, biomarker imaging, diseases therapy, and other biomedical fields.