Solid-state Fluorescence Research Articles

Water sensitive fluorescence tuning of V-shaped ESIPT fluorophores: Substituent effect and trace amount water sensing in DMSO

Highly sensitive nature of excited state intramolecular proton transfer (ESIPT) functionality in organic fluorophores made them potential candidates for developing environmental sensors and bioimaging applications. Herein, we report the synthesis of V-shaped Dapsone based Schiff base ESIPT derivatives (1–3) and water sensitive wide fluorescence tuning from blue to red in DMSO. Solid-state structural analysis confirmed the V-shaped molecular structure with intramolecular H-bonding and substituent dependent molecular packing in the crystal lattice. 1 showed strong solid-state fluorescence (λmax = 554 nm, Φf = 21.2 %) whereas methoxy substitution (2 and 3) produced tunable but significantly reduced fluorescence (λmax = 547 (2) and 615 nm (3), Φf = 2.1 (2) and 6.5 % (3)). Interestingly, aggregation induced emission (AIE) studies in DMSO-water mixture revealed water sensitive fluorescence tuning. The trace amount of water (less than 1 %) in DMSO converted the non-emissive 1–3 into highly emissive state due to keto tautomer formation. Further increasing water percentage produced deprotonated state of 1–3 in DMSO and enhanced the fluorescence intensity with red shifting of emission peak. At higher water fraction, 1–3 in DMSO produced aggregates and red shifted the emission with reduction of fluorescence intensity. The concentration dependent fluorescence study revealed the very low detection limit of water in DMSO. The limit of detection (LOD) of 1, 2 and 3 were 0.14, 1.04 and 0.65 % of water in DMSO. Hence, simple Schiff bases of 1–3 showed water concentration dependent keto isomer, deprotonated and aggregated state tunable fluorescence in DMSO. Further, scanning electron microscopic (SEM) studies of 1–3 showed water concentration controlled self-assembly and tunable fluorescence.

Recent advances in fluorescence and afterglow of CDs in matrices.

Carbon dots (CDs) are novel nanomaterials with dimensions less than 10 nm that have attracted much attention due to their outstanding optical properties. However, the development of solid-state fluorescence and afterglow methods has been relatively slow, although the properties of these materials under liquid conditions have been extensively studied. In recent years, embedding CDs in a matrix has been shown to prevent aggregation quenching and inhibit nonradiative transitions, thus realizing solid-state fluorescence and afterglow, which has greatly broadened the research and application areas of CDs. In terms of hydrogen bonding, ionic bonding, covalent bonding and spatial confinement, the interactions between CDs and matrices can effectively realize and improve the solid-state fluorescence and afterglow effects of CDs. Recent applications of CDs in matrices in optoelectronics, information security, sensing, biotherapeutics and imaging are also summarized. Finally, we summarize the challenges and developments of CDs in matrices.

Solid-state red fluorescence of intramolecularly ring-fused donor-π-acceptor-type fluorinated diphenylacetylenes achieved by enhancing intramolecular charge transfer properties

Developing efficient red fluorescent materials is crucial in various fields, such as medicine, chemical biology, and organic electronics. Molecular design strategies involving the extension of π-conjugation lower the solid-state fluorescence...

Halogen atom substitution effect on the carbazole fluorescence properties and supramolecular interactions in the solid-state

Dihalogen substituted carbazole displayed halogen bonding controlled supramolecular interactions and reduced fluorescence efficiency due to heavy atom effects.

Trivial positional isomerism in ligands triggering different properties in Fe(II)-metallopolymers; design, synthesis, and characterization.

The tunable molecular scaffold of organic moieties in metallopolymers generates variation in their properties, but what could be the minimal change that can produce variation in the properties of these macromolecules is still untouched. This research has meticulously explored the trivial change in the molecular scaffold of the ligand capable of making a mammoth difference in the nonvolatile memory and coordination pattern in two metallopolymers. The significance of this research lies in the fact that it demonstrates how a slight change in the organic building block can significantly alter the memristive and fluorescence properties of iron(II) metallopolymers, opening up new possibilities for their design and synthesis. Two novel positional isomeric ligands and their corresponding iron(II)-polymers were synthesized and thoroughly characterized using NMR, XRD, ATR-IR, FESEM, AFM and other techniques. Bright orange solid and solution state fluorescence was observed both in the solid and solution states for ligand L2 (3,3'-bis((E)-(pyridin-3-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol), while ligand L1 (3,3'-bis((E)-(pyridin-2-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol) showed blue fluorescence in the solution state only. A robust memristive property for Fe(II)-L1-poly with a high current ON/OFF ratio of 104, remarkable random access behaviour, and a long retention time greater than 35 000 seconds was observed while its counterpart was entirely silent. Both polymers showed solution-state electrochromism. These synthesised metallopolymers also showed good specific capacitance in the range of 50-60 F g-1 with a remarkable retention of 98% of the initial value even after 5000 charge-discharge cycles. The AFM and FESEM micrographs revealed the formation of long polymer nano-rods, which correlates with the NMR, ATR-IR, and XRD results. The difference in the properties of polymers generated by such a slight change in the organic building block forces different coordination patterns of these two ligands around the same central metal ion, and this is also evident in all the characterization methods.

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.

Self-reversible mechanofluorochromic AIEgens with tunable solid-state fluorescence: effect of acceptors and intermolecular interactions

The intermolecular interacting functionality in the carbazole-based π-conjugated fluorophores controlled mechano-responsive fluorescence switching.

CinNapht AIE(E)gens for selective imaging of lipid droplets.

This article describes the synthesis and photophysical properties of Aggregation-Induced Emission (enhancement) luminogens derivated from CinNaphts dyes. These fluorophores can be obtained in good yields in a single SNAr step of a fluorinated CinNapht derivative by incorporating hindered aromatic amines. They exhibit AIE(E) behavior associated with solid-state fluorescence covering an emission range from 563 to 722 nm. One carbazole derivative demonstrates a remarkable efficiency in imaging lipid droplets in living cells through an original photophysical mechanism.

Aggregation-induced generation of circularly polarized luminescence in naphthaleneimide-based nanostructures with high dissymmetry factor.

Extensive efforts have been dedicated towards designing new organic materials that display solid-state fluorescence and possess optical activity, thereby leading to the fabrication of materials emitting circularly polarized light. Existing organic materials usually suffer from two limitations, a low dissymmetry factor (glum) and weak or no fluorescence in the solid state. Herein, we have demonstrated a naphthalene imide-based dyad system that remains fluorescent even in powder form and displays circularly polarized luminescence in its aggregated and solid state with significantly high glum values.

Design, synthesis, and biological application of A-D-A-type boranil fluorescent dyes.

For the first time, three acceptor-donor-acceptor (A-D-A)-type boranil fluorescent dyes, CSU-BF-R (R = H, CH3, and OCH3), featuring phenothiazine as the donor, were designed and synthesized. CSU-BF-R exhibited remarkable photophysical characteristics, including large Stokes shifts (>150 nm), high fluorescence quantum yields (up to 40%), long-wavelength emissions, and strong red solid-state fluorescence. Moreover, these CSU-BF-R fluorescent dyes were demonstrated to function as highly selective and sensitive ratiometric fluorescent probes for detecting hypochlorous acid (HClO). The preliminary biological applications of CSU-BF-OCH3 for sensing intracellular HClO in living cells and zebrafish were demonstrated. Therefore, CSU-BF-R possess the potential to further explore the physiological and pathological functions associated with HClO and provide valuable insights into the design of high-performance A-D-A-type fluorescent dyes.

Solution and solid-state fluorescence emission from cyanostyrene molecules with multiple nitrogen atoms.

A design strategy has been proposed to utilize structure-driven solution and solid-state fluorescence emission of polynitrogen atoms. The strategy uses benzimidazole as the electron donor and pyridine as the electron acceptor to construct D-A-type cyanopyridine ethylene molecules. Theoretical calculations reveal that compound 1 has energy-close isomers in dilute solutions, with planar conformation in S0 and S1 states, reducing molecular motion and thus enhancing radiation efficiency (quantum yield up to 42.7%). Conversely, the distorted cyanobenzene structure reduces the quenching effect of π-π stacking alignment, and hydrogen bonding between molecules limits molecular vibration and rotation, ultimately leading to strong emission in the solid state (quantum yield up to 27.4%). These dual-state luminescence systems have wide-ranging potential applications in information encryption and temperature sensors.

Synthesis of High-Fluorescent Diphenyl-anthracene Derivatives and Application in Detection of Nitroaromatic Explosives and Fingerprint Identification.

The development of high-intensity fluorescent materials is always the focuses and forefront projects because of their important applications in displays, sensing and detection fields. In recent years, the detection of explosives has attracted increasing attention due to security and counterterrorism issues. Herein, two diphenyl-anthracene (DPA) derivatives were designed and synthesized by introducing strong electron withdrawing fluorine atoms and cyano-groups to DPA, which exhibited strong fluorescence both in the solution and solid phase with the absolute quantum yields up to 70.4 % and 45.9 % respectively. The detection behavior of nitroaromatic explosives such as picric acid (PA), 2,4,6-trinitrotoluene (TNT) and 3-Nitropropionic acid (3-NP) also shows good sensitivity with the quenching constant as high as 6.3×104 L mol-1 . Theoretical calculation demonstrates that the fluorescence quenching behavior of the two DPA derivatives is caused by the behavior of photoinduced electron transfer (PET) and the resonance energy transfer (RET) studies explained the higher sensitivity and selectivity of both compounds towards PA than other nitro-containing explosives. Furthermore, the strong solid-state fluorescence of the DPA derivatives also shows excellent advantages in enhancing latent fingerprint recognition.

4‐substituted push‐pull quinazoline chromophores with extended π‐conjugated linker

AbstractA series of four push‐pull compounds based on a 4‐phenylquinazoline scaffold were designed. Three of these compounds exhibit dual state emission with intense fluorescence in solution and solid state. Their emission properties are sensible to environement stimuli with intense emission solvatochromism and halochromism. In case of methoxy derivative, both neutral and protonated form are luminescent and white light emission can be observed by controlled partial protonation.

Dual state emissive tridentate imidazopyridines with applications in acidochromism, metal ions detection, data encryption, and bioimaging

Four novel tridentate scaffolds IP-nTPA (n = 1, 4, 8, and 12), in which 2,6-bis(imidazo [1,2-a]pyridin-2-yl)pyridine and alkoxyl-substituted triphenylamine (TPA) are utilized as electron-donor and electron-acceptor, respectively, have been synthesized. Due to the inclusion of flexible alkoxyl chain to suppress π–π stacking in solids, IP-nTPA (n = 1, 4, 8) displayed efficient fluorescence in both solution and solid state. Meanwhile, IP-nTPA demonstrated an obvious solvatochromism with red-shifted emission when increasing solvent polarity, which is associated with the formed intramolecular charge transfer (ICT) states in the donor-acceptor (D-A) architecture. Theoretical calculations and single crystal structure analysis were utilized to interpret the emission behaviors in both solution and solid state. Importantly, IP-4TPA was chosen as the candidate to exhibit reversible acidichromism, metal ions detection, and information security application. Finally, the bioimaging application of IP-nTPA in PC-3 cells was investigated, which showed excellent biocompatibility and cell permeability.

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.

Long-Term Imaging of Cys in Cells and Tumor Mice by a Solid-State Fluorescence Probe.

Cysteine is an important biological thiol and is closely related to cancer. It remains a challenge to develop a probe that can provide long-term fluorescence detection and imaging of Cys in cells as well as in living organisms. Here, a solid-state fluorophore HTPQ is combined with an acrylate group to construct a solid-state fluorescent probe HTPQC for Cys recognition. The fluorescence of the probe is quenched when the photoinduced electron transfer (PET) process is turned on and the excited-state intramolecular proton transfer (ESIPT) process is turned off. In the presence of Cys, an obvious solid-state fluorescence signal can be observed. The double quenching mechanism makes the probe HTPQC have the advantages of high sensitivity, good selectivity, and high contrast of biological imaging. Due to low cytotoxicity, the probe HTPQC can be used to detect exogenous and endogenous Cys in living cells and is capable of imaging over long periods of time. By making full use of long wavelengths, the probe can be applied for the detection of Cys levels in tumor mice and equipped with the ability to conduct long-term imaging in vivo.

A novel luminescent Ni(II) coordination compound for highly selective detection of acetylacetone, MnO4−, tetracycline and Ag+ in aqueous systems

A new Ni(II) compound [Ni(bim)2(H2O)4] (1,5-nds)·(H2O)0.51 (bim = benzimidazole, 1,5-nds-Na = disodium 1,5-naphthalenedisulfonate) was readily synthesized at room temperature. Although compound 1 is only a mononuclear compound, it is extended into a 2D supermolecule layer by hydrogen bonding interactions. Hirshfeld surfaces and fingerprint maps of compound 1 crystal packing were calculated to gather information on non-covalent interactions. Photoluminescence experiments showed that 1 not only possessed good solid-state fluorescence performance but also favorable fluorescence characteristics and stability in aqueous solutions, which can be exposed to acidic and alkaline environmental conditions (pH = 1–14) for a long time. Remarkably, compound 1 displayed outstanding anti-interference properties, high sensitivity, high quenching rate, and low limit of detection (LOD) against acetylacetone (acac), MnO4−, and tetracycline (TET) in water media via the Turn-Off effect (LOD:7.03 μM for acac, 2.92 μM for MnO4− and 0.65 μM for TET). Especially, compound 1 can also be used as a rare ratiometric fluorescent probe for the detection of Ag + down to the nM level. The exceptional multi-responsive performance suggested that compound 1 could be a potential multifunctional sensor. Furthermore, possible mechanisms were systematically investigated.

Rapid synthesis of functional carbon dots by microwave: Advanced information security anti-counterfeiting material

Since carbon dots (CDs) exhibit exceptional optical qualities, they have been the focus of much research. Luminescent materials based on CDs are increasingly appearing, but the realization of solid-state matrix-free long-lasting afterglow and white fluorescence remains challenging. In this work, a microwave-assisted synthesis route is used to prepare solid-state white fluorescent CDs with 6 s matrix-free dual (503 nm, 542 nm) delayed fluorescence (DF) afterglow that can be observed by naked eye which uses 1,2,4,5-benzenetetracarboxylic acid (BA) and ethanol as precursors. And polychromatic nitrogen-doped CDs (N-CDs) are prepared using tetraethylenepentamine (TEPA) as nitrogen source, and the solvent controlled synthesis is typical. The solid-state green N-CDs prepared from ethanol (E-CDs) and white fluorescence N-CDs prepared from deionized water (W-CDs) have 3.5 s and 1.2 s (527 nm, 558 nm) visible matrix-free room temperature phosphorescence (RTP) afterglow, respectively. Our work has found (n, π*) structure providing a new strategy for developing CDs as solid-state long-lasting matrix-free afterglow materials and a new reference value for their potential applications in anti-counterfeiting and information encryption.

Imidazole-based solid-state fluorescence switch: Stimuli-responsive emission, mechanochromism and acidochromism

Stimuli modulated fluorescence properties of imidazole-based molecular probe (E)-2-(5,5-dimethyl-3-(4-(1,4,5-triphenyl-1H-imidazole-2-yl)styryl)cyclohex-2-en-1-ylidene)malononitrile (Ph-ISO) in the solid state is presented. Not only did the probe display aggregation induced emission (AIE) activity with intense solid-state fluorescence emission, but also exhibited several repetitive cycles of reversible mechanochromism as well as acidochromism. The solid-state emission is ascribed to the intermolecular interactions in the highly twisted conformation of Ph-ISOviamultiple C–H---N and C–H---π interactions as confirmed by the single crystal X-ray analysis. The applied mechanical stress in the form of grinding results in the transformation of crystalline state to the amorphous state with a red shifted emission band attributed to attaining more planar conformation vs twisted conformation, with extended molecular conjugation. While reversible mechanochromism makes the probe suitable for rewritable papers, the switchable acidochromism is useful for theon-sitemonitoring of pH differences in biological and environmental media.

Solid superacid catalysts promote high-performance carbon dots with narrow-band fluorescence emission for luminescence solar concentrators

Facile and efficient method for constructing carbon dots (CDs) with narrow full width at half maximum (FWHM) is a major challenge in the field, and researches on regulating the FWHM of CDs are also rare and scarce. In this work, we delved into the synthesis of CDs with narrow fluorescence emission FWHM (NFEF-CDs) in the m-phenylenediamine (m-PD)/ethanol system, utilizing solid superacid resin as catalyst with solvothermal method. The resulting NFEF-CDs exhibit a photoluminescent (PL) emission peak at 521 nm with a narrow FWHM of 41 nm, an absolute PL quantum yield (QY) of 80%, and display excitation-independent PL behavior. Through comprehensive characterization, we identified the protonation of edge amino on NFEF-CDs as the key factor in achieving the narrow FWHM. Subsequently, we validated the broad applicability of solid superacid resins as catalysts for synthesizing CDs with narrow FWHM in the m-PD/ethanol system. Finally, we utilized a self-leveling method to prepare NFEF-CDs film on the surface of poly(methyl methacrylate) (PMMA) substrate and investigated the solid-state fluorescence properties of NFEF-CDs as well as their performance as luminescence solar concentrator (LSC) for photovoltaic conversion. The results revealed that the as-prepared LSC exhibit an internal quantum efficiency (ηint) of 42.39% and an optical efficiency (ηopt) of 0.68%. These findings demonstrate the promising prospects of NFEF-CDs in the field of LSCs and provide a theoretical basis for their application in photovoltaic conversion.