Solid-state Fluorescence Quantum Yield Research Articles

Synthesis and properties of chiral liquid crystal copolymers with tunable circularly polarized luminescence

Chiral liquid crystals have received widespread attention due to their unique advantages in improving circularly polarized luminescence (CPL) properties. However, how to achieve the emission and modulation of CPL for chiral liquid crystals within intrinsic polymer-based materials through a simple strategy remains a challenge. This article proposes a simple and feasible method to synthesize CPL chiral liquid crystals and manipulate their properties by copolymerizing chiral liquid crystal monomer with luminescent monomer. A series of intrinsic chiral luminescent liquid crystal copolymers C*(x)-Py(y) with tunable CPL performance were synthesized by copolymerizing chiral liquid crystal monomer MA6C* with pyrene-based luminescent monomer MC6Py in varying ratios. The effective control of the chiral liquid crystal phase structure and CPL performance of the copolymers C*(x)-Py(y) can be achieved by altering the composition of copolymers. In the copolymers, the CPL signal is generated due to the helix induction of pyrene chromophores by the chiral liquid crystals, and the CPL signal can be inverted and amplified by the unique selective reflection properties of chiral liquid crystals. For copolymer C*(0.75)-Py(0.25), the luminescence dissymmetry factor value and solid-state fluorescence quantum yield can reach −0.052 and 43.12%, respectively.

Tunable multi-peak emission solid-state fluorescent carbon dots: Luminescence regulation mechanism and application in single-component-based LEDs

The design of solid-state fluorescent carbon dots (CDs) with multi-peak emission has become an urgent challenge to be solved with the in-depth research of CDs in LEDs. Here, one- and two-component solid-state white light CDs are synthesized by microwave-assisted hydrothermal method using the biological pollutant cyanobacteria, respectively. The solid-state fluorescence quantum yield of the one-component CDs was as high as 41.8 %, and the solid-state fluorescence mechanism of CDs is discussed to be mainly attributed to the self-quenching-resistant feature of “core-shell” structure and the reabsorption/RET-induced long-wavelength red light emission, and attenuation of the short emission wavelength. For two-component white light CDs, blue- and red-light CDs are obtained by simple dialysis separation, realizing the fluorescence tunability. The different origins of their multi-peak emission are discussed: core, edge and surface states. The synthesis yields of CDs are up to 62 %, enabling stable gram-scale production. The white- and red-light CDs are used as phosphors to fabricate fluorescent films and cold, pure, and warm white- and red-light LEDs with good resistance to photobleaching and temperature stability and CRI of 84.4, 85.7 and 61.5.

Novel triphenylamine-pyrene-based AIEgens: Specific detection and imaging of H2O2 in aqueous solution and cells

H2O2 plays a key regulatory role as a bioendogenous reactive oxygen species in cells and organisms. However, excessive production or accumulation of H2O2 during mitochondrial oxidative stress may lead to oxidative damage of cellular proteins and trigger rheumatic diseases, cancers, and a variety of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. In addition, H2O2 is a very useful chemical widely employed in the textile and chemical industries, and its excessive emission not only pollutes the environment but also jeopardizes human health. Therefore, the sensitive and specific detection and removal of H2O2 is important for early diagnosis of diseases, treatment prognosis and environmental pollution monitoring. We have designed two novel triphenylamine-based AIEgens MOTPP and MOTPP-B, which each have a high solid-state fluorescence quantum yield and excellent aggregation-induced emission properties. MOTPP-B has high selectivity and anti-interference ability toward H2O2, a wide pH tolerance range, a sensing process that is complete in under 40 min, and a low detection limit of 120.77 nM. It has been successfully applied for the detection of low concentrations of H2O2 in the environment and to dual-channel imaging of low concentrations of exogenous H2O2 in living cells.

Impact of the phenyl on fluorescence properties of cyanostilbene modified tetraphenylethene compounds

Two novel cyanostilbene-modified tetraphenylethene derivatives were constructed by Williamson etherification, Suzuki coupling and Knoevenagel condensation reactions. Both compounds exhibited aggregation-induced emission and strong solid-state fluorescence behaviors with extremely high fluorescence quantum yield due to the distorted molecular conformation. Strangely, the compound without additional phenyl spacer did not show mechanochromic behavior, whereas, the compound with an additional phenyl spacer exhibited distinct mechanochromic behavior with the red-shifted emission wavelength from 480 nm to 503 nm upon grinding. The distinct differences in mechanochromic behaviors between the reported compounds could be attributed to that the additional phenyl spacer had benefits for the molecular planarization with external mechanical force. This investigation provided a method to construct mechanochromic material with aggregation-induced emission behavior and high solid-state fluorescence quantum yield and promoted the utilization in rewritable luminescent paper.

Aminoguanidine-based bioactive proligand as AIEE probe for anticancer and anticovid studies.

The emission features of a novel bioactive compound, 1,3-bis(2-hydroxy-3,5-diiodophenyl-methylideneamino)guanidine is found impressive with aggregation induced emission enhancement. The nitrogen and iodine rich multidentate proligand was characterized physicochemically. SCXRD and Hirshfeld surface investigation have revealed the presence of significant triangular iodine bonding apart from hydrogen bonding, weak C-H⋯π and π⋯π intermolecular interactions. These interactions collectively contribute to the solid-state packing arrangement of the molecules within the crystal lattice. The band gap of the compound was estimated experimentally and is supported with theoretical calculations. The solid-state fluorescence quantum yield of Φ = 0.36 emphasizes the utility of the proligand and the AIEE characteristics is attributed to restricted intramolecular motions as indicated by fluorescence lifetime decay studies. Strong interaction of the compound with calf thymus DNA was explored experimentally and found to align with in silico docking results. Notably, in vitro anticancer assessment on MCF-7 breast cancer cells show an IC50 value of 181.05 μg mL-1 and signifying its potent cytotoxic properties. Also, the compound is found to have lesser cytotoxicity against L929 normal cell line with an IC50 value of 356.54 μg mL-1. Computational studies further underscore the exceptional binding affinity with active sites in the SARS-CoV-2 main protease 3CLpro, surpassing established repurposed drugs. Furthermore, the proligand demonstrates excellent putative affinity towards the SARS-CoV-2 spike glycoprotein, accompanied by its distinctive AIEE attributes, drug likeness and DNA binding capability rendering it a valuable tool for prospective research investigations.

Anion-directed cationic supramolecular dyes with reversible mechanochromism and fabric staining

It is vital to create supramolecular dyes with excellent photo-luminescence properties based on host-gust interaction. In this study, we present three novel self-assembled cationic supramolecular dyes driven by host-guest electrostatic interaction and with ultrasmall cavities. These cationic dyes were developed and synthesized using pyridine-substituted phenanthrene, triphenylamine (TPA), and tetraphenyl ethylene (TPE) as chromophores through the pyridine quaternary ammonium salt reaction. These anion-trapped supramolecular dyes exhibit outstanding aggregation-induced emission (AIE) characteristics as well as reversible mechanochromism behavior and high solid-state fluorescence quantum yields (∼60.87 %). Furthermore, the cationic supramolecular dyes directly stain cotton fibers with 50 % dyeing rate in water-methanol solutions, in which the deprotonated glucose-O- guest possibly interacts with the cationic dye through host-guest encapsulation. Additionally, we characterized the dyeing process through IR spectroscopy, UV–vis spectroscopy, fluorescence spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Due to the reversible, tractable, and high-contrast mechanochromism of the dyes, they can make up a color-changing flower pattern. Thus, we anticipate that these dyes will have potential applications in information security storage and anti-counterfeiting.

Encapsulating carbon dots in polymethyl methacrylate nanoparticles toward improved solid-state fluorescence quantum yield

In this paper, we prepare carbon dots (CDs) through hydrothermal method, and then the CDs are encapsulated in polymethyl methacrylate (PMMA) nanoparticles through the suspension polymerization of MMA nanodroplets, obtaining a CD/PMMA nanocomposite with a CD concentration of 0.3 wt%. The CDs of the nanocomposite are confined in the PMMA nanoparticles, so there is no excessive resonance energy transfer or direct π-π interaction among the CDs in different nanoparticles, weakening the aggregation caused quenching compared with conventional CD/PMMA composite fabricated by directly blending the CDs with bulk PMMA. Consequently, the quantum yield (QY) of this CD/PMMA nanocomposite is higher than that of the conventional CD/PMMA composite, and even very close to that of the dilute CD solution. This study may provide a universal method to prepare CD/polymer solid-state fluorescent materials with higher QYs compared with conventional CD/polymer composites prepared through direct blending CDs with bulk polymers.

The effect of –CF3 substitution position on the aggregation-induced emission, solvatofluorochromism and mechanofluorochromism properties of the conjugated 9-butyl-9H-carbazole phenylacrylonitrile derivatives

A series of 9-butyl-9H-carbazole derivatives with intense solid-state emission were synthesised by the Knoevenagel reaction of 9-butyl-9H-carbazole-3-carbaldehyde with phenyl acetonitrile derivatives with –CF3 group at different substituent positions of the phenyl group. They exhibit remarkable aggregation-induced emission (AIE), solvatofluorochromism and mechanofluorochromic (MFC) properties depending on the –CF3 substitution site. The ortho-substituted derivative shows enhanced charge transfer properties with a distinct dual-state fluorescence emission. This peculiar property is further utilised for data encryption and anti-counterfeiting applications. The para-substituted derivative exhibits an increased solid-state fluorescence quantum yield of 88% with switchable MFC properties. The ground and excited state photophysical properties of the synthesised luminogens were explored using various spectroscopic techniques. The study provides an efficient strategy to understand the effect of the –CF3 substitution position in tuning and modifying the luminescence properties of the organic solids via subtle modifications in the molecular scaffolds.

Room-temperature synthesis of a covalent organic framework with hydrazine linkages for sensitive fluorescent detecting and renewable removing of copper ions

A hydrazone bonded covalent organic framework (TFPB-DHzDs) was successfully synthesized with acetic acid as the catalyst and acetonitrile as the solvent at room temperature. It was proved that TFPB-DHzDs has good crystallinity and stability, as well as excellent luminescence properties. The solid-state absolute fluorescence quantum yield of TFPB-DHzDs was 6.19%. It is found that copper ions have a specific strong fluorescent quenching effect and can be absorbed by TFPB-DHzDs, which makes it possible for the selective sensing of copper ions. The TFPB-DHzDs COF exhibited excellent ability to determine Cu2+ in aqueous solution ranging from 0.1 to 5 μM with the detection limit of 47.8 nM. Furthermore, TFPB-DHzDs was also proved to be an excellent porous adsorbent for Cu2+ in water matrix and the maximum adsorption capacity is 203 mg g−1. The recycling use of TFPB-DHzDs for detecting and removing of Cu2+ can be easily realized by adding a chelating agent. And it can be recovered and recycled at least six times. This work explores the attractive potential of COF TFPB-DHzDs simultaneously as a sensitive fluorescent sensor and an efficient sorbent material, which broadens the application of COFs in fluorescence sensing, metal removal, and environmental analysis.

Systematic Study of Solid-State Fluorescence and Molecular Packing of Methoxy-trans-Stilbene Derivatives, Exploration of Weak Intermolecular Interactions Based on Hirshfeld Surface Analysis

In recent years, fluorescent compounds that emit efficiently in the solid state have become particularly interesting, especially those that are easily prepared and inexpensive. Hence, exploring the photophysical properties of stilbene derivatives, supported by a detailed analysis of molecular packing obtained from single-crystal X-ray diffraction data, is a relevant area of research. A complete understanding of the interactions to determine the molecular packing in the crystal lattice and their effect on the material's physicochemical properties is essential to tune various properties effectively. In the present study, we examined a series of methoxy-trans-stilbene analogs with substitution pattern-dependent fluorescence lifetimes between 0.82 and 3.46 ns and a moderate-to-high fluorescence quantum yield of 0.07-0.69. The relationships between the solid-state fluorescence properties and the structure of studied compounds based on X-ray analysis were investigated. As a result, the QSPR model was developed using PLSR (Partial Least Squares Regression). Decomposition of the Hirshfeld surfaces (calculated based on the arrangement of molecules in the crystal lattice) revealed the various types of weak intermolecular interactions that occurred in the crystal lattice. The obtained data, in combination with global reactivity descriptors calculated using HOMO and LUMO energy values, were used as explanatory variables. The developed model was characterized by good validation metrics (RMSECAL = 0.017, RMSECV = 0.029, R2CAL = 0.989, and R2CV = 0.968) and indicated that the solid-state fluorescence quantum yield of methoxy-trans-stilbene derivatives was mainly dependent on weak intermolecular C…C contacts corresponding to π-π stacking and C…O/O…C interactions. To a lesser extent and inversely proportional, the fluorescence quantum yield was affected by the interactions of the type O…H/H…O and H…H and the electrophilicity of the molecule.

Anomalous deep-red luminescence of perylene black analogues with strong π-π interactions

Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close π−π stacking arrangement. However, contrary to the luminescent monomers, deep-red and black PBI pigments are commonly non- or only weakly fluorescent due to (multiple) quenching pathways. Here, we introduce N-alkoxybenzyl substituted PBIs that contain close π stacking arrangement (exhibiting dπ−π ≈ 3.5 Å, and longitudinal and transversal displacements of 3.1 Å and 1.3 Å); however, they afford deep-red emitters with solid-state fluorescence quantum yields (ΦF) of up to 60%. Systematic photophysical and computational studies in solution and in the solid state reveal a sensitive interconversion of the PBI-centred locally excited state and a charge transfer state, which depends on the dihedral angle (θ) between the benzyl and alkoxy groups. This effectively controls the emission process, and enables high ΦF by circumventing the common quenching pathways commonly observed for perylene black analogues.

Bright and multicolor emissive carbon dots/organosilicon composite for highly efficient tandem luminescent solar concentrators

Carbon dots (CDs) hold great promise for effective alternatives to traditional luminescent materials in the field of luminescent solar concentrators (LSCs) due to their low cost, eco-friendly and stability. How to improve the performance of CDs based LSCs is the research focus at present. Herein, a novel CDs/organosilicon composite (SiCDs) with tunable solid-state fluorescence and photoluminescence quantum yield from 21% to 56% is reported to cope with the limitation of aggregation-caused quenching of CDs on the performance improvement of LSCs. The emission redshift mechanism of SiCDs have been explored in detail. Furthermore, the UV absorption of SiCDs is in wide range and gradual increase in intensity as the emission red shifted from blue to orange. The SiCDs are further designed to construct a series of transparent single-layer and tandem LSCs with polydimethylsiloxane as waveguide material, and the tandem LSC based on blue and yellow emission SiCDs achieve a finally external optical efficiency of 7.10%.

Lanthanoid hydrogen-bonded organic frameworks: Enhancement of luminescence by the coordination-promoted antenna effect and applications in heavy-metal ion sensing and sterilization

Enhancing the antenna effect to increase energy transfer to lanthanoid ions for generating bright luminescence is an effective strategy to construct lanthanoid luminophores with excellent performance. However, the antenna effect often depends on the structure, connection, and configuration of immobilized ligands. We found for the first time that the introduction of the Zn(II) ion coordination can greatly enhance the solid-state fluorescence and phosphorescence emission of lanthanoid hydrogen-bonded organic frameworks (Ln-HOFs). Notably, relative to that of Tb-HOF, the solid-state fluorescence intensity, quantum yield, and lifetime of TbZn-HOFs had increased by 17.09, 38.81, and 12.96 times, respectively. The chelating coordination of the Zn(II) ions effectively hindered the vibration of organic ligands to weaken nonradiative transitions and stabilized and reduced the triplet excited state of the ligands through the spin–orbit coupling effect, which led to the increased efficiency of energy transfer with Tb(III) ions. In aqueous solution, LnZn-HOFs released Ln(III) ions effectively and captured low concentrations of the heavy metal ion Cu(II), and the efficient ligand-to-Cu(II) ion energy transfer quenched ligand luminescence. Notably, the limit of detection (LOD) was calculated to be 1.91 nM, which was considerably lower than the maximum level of Cu(II) ions in drinking water (20 μM) specified by the United States Environmental Protection Agency and was better than the LOD of other previously reported probes. Furthermore, LnZn-HOFs can effectively inhibit the proliferation of classical Gram-positive bacteria, such as Bacillus subtilis and Staphylococcus aureus, via ion release and thus showed a high sterilization effect. This work is the first to find that HOFs can exert efficient bacteriostatic and sterilization effects through ion release.

Rational design of water-soluble supramolecular AIEgen with ultra-high quantum yield, and its application in α-amylase activity detection and wash-free lysosome imaging

A class of AIEgens with D-π-A structure and high quantum yield was designed and synthesized, in which the solid-state fluorescence quantum yield of TTAM was as high as 58.30% in the study. The supramolecular AIEgen TTAM β-CDs constructed by a simple method could be used for the detection of α-amylase activity, wash-free lysosomal imaging and lysosomal dynamic monitoring. The assay has the advantages of easy manipulation, high sensitivity (LOD = 0.007902 U·mL−1) and high specificity. TTAM β-CDs method was successfully applied to the determination of α-amylase activity in human oral saliva with high accuracy, which was almost error-free compared to commercial method. It was found that TTAM β-CDs, with a high lysosomal colocalization coefficient (0.91) in HeLa cells, was not only avoid the tedious water washing process but also reduce the interference of cell secretions on lysosomal imaging signals in the study of lysosomal imaging, and its precise monitoring of lysosomal translocation was of great significance for the study of tumor invasion and metastasis.

Color-tuning and manipulation of the aggregation-induced emission efficiency of o-carborane-tetraphenylethylene dyads through substituted o-carboranes

By changing the 2-R substituents of carborane, absolute solid state fluorescence quantum yields of TPE derivatives ranging from 18% to 91% were obtained. The emission colors show a clear shift from blue to red with a maximum red shift of 239 nm.

Color-tunable and Highly Emissive Solid Materials Constructed from Tetraphenylethylene-o-carborane-based Building Blocks: Synthesis, Aggregation-induced emission, and Photophysics.

A novel kind of expanded tetraphenylethylene (TPE)-carborane-TPE pentad has been synthesized by using two adjacent carborane moieties as central bridges and three TPE units in lateral positions. Its solid-state fluorescence quantum yield was substantially increased to 68.2% by expanding the number of bridges between carborane and TPE. Subsequently, the emission color shifted from blue to orange-yellow (126 nm). Mechanical insights into the electronic structure of the extended TPE-carborane-TPE pentads were obtained from density functional theory (DFT) calculations.

Naphthalimide-Based Hydrazone Derivatives: Synthesis, Mechanochromism in the Solid State and Response to Ions in Dilute Solutions.

Molecules showing mechanochromic luminescence (MCL) are promising for use in the in the fields of sensing and probes. We report the design and synthesis of new naphthalimide-based hydrazone derivatives, NI-TPE and NI-3BA. Both the luminogens are weakly emissive with s Φf =0.3 % and 0.5 % respectively when aggregated in amorphous states as strong π-π stacking and intermolecular interaction prevent luminescence. On the contrary, in the crystalline state, single crystal analysis of two derivatives shows that nonradiative decay is reduced or inhibited by molecular stacking modes and intermolecular interactions. Increases of fluorescence emission intensity to s Φf =5.5 % and 6.0 % upon solvent evaporation are attributed to weak π-π overlapping and hydrogen bonding (N-H ⋅⋅⋅ O, distance 2.99 Å), which are beneficial to the formation of molecules with a loose packing. At the same time, the packing modes that the two derivatives adopt in the crystal lattice are destroyed to result in a low solid-state fluorescence quantum yield and a bathochromic shift of 23-25 nm upon grinding. All these factors cause the two derivatives show an unusual "turn off" MCL phenomenon. The fluorescence emission, its pH reversibility, and selective response to fluoride and acetate ions of up to 91-93 % in dilute solutions were also demonstrated.

Configuration-controllable synthesis of Z/E isomers based on o-carborane-functionalized tetraphenylethene

Two Z/E isomers, namely, Z-TPE-2Car and E-TPE-2Car, with clear configuration were synthesized using an effective route and have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.

Mechanoluminescence and aggregation-enhanced emission (AEE) of an In-MOF based on a 9,9'-diphenyl-9H-fluorene tetraacid linker.

A water-stable In-MOF, constructed based on a conformationally-flexible tetraacid linker, i.e., 2,7-bis(3,5-dicarboxyphenyl)-9,9'-diphenyl-9H-fluorene, i.e., H4DPF, is shown to exhibit a significantly enhanced solid-state fluorescence quantum yield (φf) of 23% in comparison with that of the linker (φfca. 4%) as a consequence of rigidification of the latter by metalation. Application of external stimulus in the form of grinding of the In-MOF leads to a drastic enhancement by 29%, φf from 23 to 52%. Solid-state absorption and emission spectra show that the absorption in the region of 368-550 nm gets diminished with a concomitant change in the emission maximum with a blue shift upon grinding. Fluorescence enhancement with grinding is correlated with a gradual reduction in the size of the particles, as established by SEM analysis. MOF particle aggregation has been invoked to account for the observed fluorescence enhancement in addition to a subtle conformational change in the structure of the linker upon grinding. Intriguingly, the ground MOF particles exhibit aggregation behaviour in the DMF-water solvent system with the emission further increasing up to 75% for the increase in the water fraction (fw) from 0 to 60%; hydrophobic aggregation of particles evidently leads to a change in the conformation of the linker and particle aggregation-enhanced emission (AEE). De-aggregation of particles ensues for fw = 70-90%, as reflected by a gradual decrease in the emission intensity. It is shown that the suspension of ground In-MOF particles in water permits sensing of metal ions, in particular Al3+ ions, by fluorescence quenching with detection at a sub-ppb level. The observed results comprise first demonstration of both mechanoluminescence and AEE of MOF particles.

Relationship between Crystal Packing and Solid-State Fluorescence Quantum Yield in Pyrazine Monoboron Complexes

Relationship between Crystal Packing and Solid-State Fluorescence Quantum Yield in Pyrazine Monoboron Complexes