Fluorescence Emission Behavior Research Articles

Red-emissive carbon dots from Hibiscus rosa-sinensis: a detailed appraisal of tartrazine dye sensing properties.

Aneconomically viable and greener approach is introduced to fabricate red emissive carbon dots (R@CQDs) via employing hydrothermal means on Hibiscus rosa-sinensis leaves as precursor source. The obtained R@CQDs displayed excitation-dependent behavior, with high aqueous stability, quantum yield of 56%, and outstanding fluorescence aptitude under the conditions of varied range of ionic strength and pH (1-12). The fluorescence emission behavior of R@CQDs displayed selective turn off fluorescenceresponse to tartrazine over other interfering species with alimit of detection of 0.09µM and quantitation limit of 0.30µM. Theoretical calculations employing density functional theory (DFT) were carried out to complement experimental findings and getting insights into the underlying mechanism governing the sensing of tartrazine. The developed sensor holds significant potential for tartrazine detection in real samples and offering wider prospective in the food safety assessment.

Fabrication and Efficient Interfacial Assembly of Bright Red-Emitting Carbon Quantum Dots for Security-Warning Textiles.

Carbon quantum dots (CQDs) have attracted more attentions due to their multiple performances. However, the fabrication of long-wavelength emitting CQDs with aliphatic precursors still remains a challenge, mainly because it is difficult to generate large sp2 domains to reduce energy gap, which is not conducive to a redshift of the luminescence peak. Hereon, by regulating the pH of citric acid and thiourea mixture, a N, S co-doped CQD emitting bright red fluorescence at 635nm is successfully fabricated through the solvothermal reaction under acidic condition, achieving a high quantum yield of 32.66%. Solvatochromic effects of the CQDs are discussed through theoretical equations and models, which confirm that the hydrogen-bonding interaction dominates the fluorescence emission behavior of CQDs in polar solvents. Besides, a feasible strategy is proposed to prepare an anti-counterfeiting textile via the deposition of red-emitting CQDs onto cotton fibers, through rapidly evaporating the preferred organic solvent. As expected, the CQD-decorated textiles exhibit encouraging anti-counterfeiting and security-warning functions, along with underwater and long-distance detectability, washability, and sun resistance. It is worth noting that the present work is innovative in realizing the application of red-light-emitting CQDs in the fields of security-warning textiles.

Stress-induced fluorescence in diamond at ultrahigh pressures and low temperatures

Diamond is widely used as an anvil material in high pressure experiments, such as diamond anvil cell (DAC). The study of the fluorescence emission behaviour of the diamond at high pressure is of great significance for understanding its band structure and optical properties. Here, by combining low-temperature photoluminescence experiments, and fluorescence spectroscopy at controlled pressure (181 GPa–122 GPa) and temperature (296 K–77 K) reveals the relationship between stress-induced diamond fluorescence as a function of temperature and pressure. We also demonstrate that the electron-phonon interaction has an effect on the diamond energy gap, and the temperature and pressure jointly affect the band structure. The electron band gap decreases rapidly under low temperature and high-pressure conditions.

Preparation of pH-responsive fluorescent carbon dots under extreme alkaline conditions

Carbon dots (CDs) were prepared via a one-step solvothermal method using L-aspartate as the carbon source and ammonia as the solvent. The prepared CDs exhibited pH-sensitive properties and a color changing response to extreme alkaline pH ranges (12.0–14.0). O-related defect and N-related defect states induced by the protolated amino groups on the CD surfaces alternately dominated the fluorescence emission with a change in pH value, and the luminescence of different defect states was greatly affected by the excitation wavelength, which endowed the CDs with different pH-dependent fluorescence emission behavior under different light excitation. Based on the fluorescent emission behavior, which could be adjusted with a change in pH, the CDs showed potential application value as an instant inspection.

Nitrogen-doped carbon dots for 3D printed smartphone-assisted cascade visual detection of morin and aluminium ion, solid fluorescence ink

With the growing emphasis on health management, individuals increasingly focus on monitoring drug molecular residues and harmful ions. Motivated by the concepts of the intelligent system and quantitative detection, we develop a smartphone-assisted cascade visual sensing device based on nitrogen-doped carbon dots (N-CDs) for in-site quantitative detection of morin and aluminium ion (Al3+). Initially, citric acid and o-phenylenediamine are identified as precursors for N-CDs synthesis via the microwave-assisted hydrothermal treatment. Subsequently, systematic studies reveal that the fluorescence of N-CDs is quenched upon the introduction of morin because of the inner filter effect (IFE). Conversely, the fluorescence recovery phenomenon occurs after the cascade addition of Al3+ since the morin binds with Al3+, resulting in the inhibition of IFE. Simultaneously, the fluorescence recovery of N-CDs enhances the cyan fluorescence emission of morin/Al3+. Based on the fluorescence quenching and recovery behavior, morin and Al3+ can be detected in the ranges of 0.070–50 μM and 0.124–40 μM with low detection limits of 0.070 μM and 0.124 μM, respectively. Furtherly, a smartphone-assisted cascade visual sensing device is designed for in-site quantitative detection of morin and Al3+. Moreover, based on the strong fluorescence and concentration-dependent emission behavior of N-CDs, the multi-color fluorescent ink is developed successfully. This work not only offers an excellent solution for simultaneous detection of morin and Al3+ but also shows numerous opportunities for solid lighting, information encryption and flexible optics.

Mechanofluorochromic behaviors and data security protection properties of salicylaldimine-based difluoroboron complexes with different aryl substituents.

To further explore the relationship between aryl substituents and mechanofluorochromic (MFC) behaviors, four salicylaldimine-based difluoroboron complexes (ts-Ph BF2, ts-Ph-NA BF2, ts-2NA BF2, and ts-triphenylamine [TPA] BF2), including aromatic substituents with different steric hindrance effects, were designed and successfully synthesized. Four complexes with twisted molecular conformation displayed intramolecular charge transfer and aggregation-induced emission properties. Under external mechanical stimuli, the as-synthesized powders of ts-Ph BF2, ts-Ph-NA BF2, and ts-TPA BF2 exhibited redshift fluorescence emission behaviors, and ts-Ph BF2 and ts-TPA BF2 could be recovered to original shifts by fuming, but ts-Ph-NA BF2 displayed irreversible switching. ts-2NA BF2 had no change during the grinding and fuming processes. The results indicated that the MFC behaviors could be attributed to the phase transformation between the well-defined crystalline and disordered amorphous states by X-ray diffraction measurement. Further research illustrated that ts-TPA BF2 with the most significant MFC phenomenon could be applied in data security protection in ink-free rewritable paper.

Synthesis of octa-benzothiazole functionalized tetraphenylethylene and their explosive sensing properties

The detection of nitroaromatic compounds (NACs) such as 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) is critical for environmental monitoring and security, due to their extensive use in explosives and the associated health risks. However, current methods for detecting these compounds face challenges in sensitivity, specificity, and practicality. In this study, a new benzothiazole functionalized tetraphenylethylene molecular scaffold (TPE-BTH) have been successfully synthesized and characterized for its potential in explosive sensing. The TPE-BTH compound exhibits distinct UV–Visible and fluorescence emission behaviors in different solvent polarities. A remarkable feature of TPE-BTH is its pronounced fluorescence quenching upon the addition of 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) in a dichloromethane solution, highlighting its sensitivity and potential utility in explosive detection. The detection limits for TNP and DNP were determined to be remarkably low at 7.28 × 10-8 M and 1.23 × 10-8 M, respectively. Through theoretical investigations, we explored the interaction mechanisms between TPE-BTH and TNP, uncovering the roles of internal hydrogen bonding within picric acid and π-π interactions as well as dipole interactions between the molecules. Additionally, 1H NMR was utilized to elucidate the interaction mechanisms between TPE-BTH and TNP. The development of TPE-BTH as a molecular scaffold for NAC detection significantly contributes to the field of explosive sensing and environmental monitoring.

Through-Space Charge-Transfer-Based Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence in Fused 2H-Chromene Coumarin Congener Generating ROS for Antiviral (SARS-CoV-2) Approach.

Harvesting triplets in metal-free organic frameworks at ambient conditions and finding appropriate applications are a formidable challenge. Herein, we report a donor-acceptor-type system composed of carbazole and fused 2H-chromene coumarin derivative, exhibiting triplet harvesting thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) behavior in solid and aggregated states, respectively. The presence of an sp3 linker and the introduction of a selected cyano/ester group in the acceptor result in twisted D-A architectures, further assisting in the suppression of nonradiative deactivation via through-space charge transfer and H-bonding interactions, fulfilling the stringent requirements for the simultaneous process of TADF and AIE, successively. Experimental and theoretical results revealed that the participation of the singlet/triplet charge transfer (1CT/3CT) and the higher lying hybrid triplet locally excited charge-transfer state (3LE + 3CT) leads to an efficient TADF. Both of the synthesized AIE-TADF congeners actively participated in the generation of reactive oxygen species (ROS) in nanoaggregate forms and were further explored computationally for antiviral prospects as inhibitors of the SARS-CoV-2 spike protein.

Preparation and Application of a Fast, Naked-Eye, Highly Selective, and Highly Sensitive Fluorescent Probe of Schiff Base for Detection of Cu2+

A fluorescent probe, N′-((3-methyl-5-oxo-1-phenyl-4, 5-dihydro-1H-pyrazol-4-yl) methylene)-2-oxo-2H-chromene-3-carbohydrazide (MPMC), was synthesized and characterized. Characterizations of the synthetic MPMC were conducted via proton nuclear magnetic resonance (1HNMR) spectroscopy and carbon-13 nuclear magnetic resonance spectroscopy (13C NMR). The fluorescence emission behaviors of the MPMC probe towards diverse metal ions were detected, and the probe exhibited high sensitivity and selectivity towards Cu2+ over other metal ions via the quenching of its fluorescence. Furthermore, the existence of other metal actions made no apparent difference to the fluorescence intensity of the MPMC-Cu2+ system; that is, MPMC displayed a good anti-interference ability. Job’s plot of the MPMC and copper ions indicated that the detection limit was 10.23 nM (R2 = 0.9612) for the assayed actions, with a stoichiometric ratio of 1:1 for MPMC and Cu2+. Additionally, the color of the MPMC probe solution changed from nearly colorless to yellow in the presence of Cu2+ in visible light, and the color change could be observed by the naked eye. Similarly, the color resolved from bright yellow into blue in ultraviolet light. Moreover, reusability studies indicated that the MPMC probe was reusable. The pH effect of the MPMC probe on Cu2+ had a broad range of pH detection, i.e., from 4.0 to 11.0. The response time of the MPMC probe for determining Cu2+ was within 1 min. The recognition of Cu2+ via MPMC performed on pre-treated paper under sunlight and UV light both had a distinct colour change. Thus, the solid-state method for detecting Cu2+ with the naked eye was both economical and convenient.

Thiophene-conjugated benzothiazole derivatives as versatile skeletons for staining subcellular organelles in living cells

A series of hydroxy thiophene-conjugated benzothiazole derivatives (HTBs) was prepared to investigate their fluorescence emission behaviors and capability to selectively stain subcellular organelles for fluorescence imaging. The HTB derivatives exhibited excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) behaviors, according to their molecular structure. Subtle changes in the molecular structure of the HTB influenced its response to changes in the surrounding environment, such as the solvent polarity and/or pH. In vitro cellular imaging experiments revealed that HTBA (5-(benzo[d]thiazol-2-yl)-[2,2′-bithiophen]-4-ol) could selectively stain mitochondria. In contrast, HTBB-CO2Et (ethyl 5'-(benzo[d]thiazol-2-yl)-3′-hydroxy-[2,2′-bithiophene]-5-carboxylate), which contains a regioisomeric hydroxy thiophene unit with an electron-withdrawing ethyl ester group, showed the capability to stain lipid droplets (LDs) in living cells. When the hydroxyl group in HTBB-CO2Et was protected with a benzyl group, effective staining of LDs in live cells was achieved. Thus, we successfully obtained an effective fluorescent probe. Collectively, the results indicated that small structural changes resulted in substantial changes in the intracellular localization and in vitro imaging ability of the prepared compounds.

Host-Guest Complexes of Pillar[5]arene as Components for Supramolecular Light-Harvesting Systems with Tunable Fluorescence.

A guest molecule containing a short alkyl spacer between the tetraphenylethylene group and the methylpyridinium group was designed and synthesized. After complexation with a water-soluble pillar[5]arene, the resulting host-guest complex can further self-assemble into fluorescence-emitting nanoparticles in water. By loading a commercially available dye Rhodamine 6G into the nanoparticles, an efficient artificial light-harvesting system with high donor/acceptor ratios (>400/1) was successfully constructed. The obtained systems show considerable antenna effects with values of more than 10 times. The system also exhibits tunable fluorescence emission behavior and can be used as a fluorescent ink for information encryption.

Physico‐chemical Properties and Anticancer Activity of Carborane‐BODIPY Conjugates: A Review

AbstractCarboranes and BODIPYs are the well known boron containing compounds. Both are relatively easy to functionalize, and small modification in their structures allow turning of their spectroscopic properties readily suggest the importance of carborane‐BODIPY conjugates. The combination of boron rich carborane and photosensitizers activatable BODIPYs have potentials for adequate boron delivery to the cancer tissues for successful cancer therapy. This review covers the most recent development of carborane‐BODIPY conjugates in space electronic energy transfer, photoinduced electron transfer, fluorescence emission and AIE behaviors, and as promising BNCT agents. Given the high potential and flexibility of this carborane‐BODIPY conjugates, we believe that major developments are to be expected in the field of both material and medicinal science.

Regulation of the supramolecular self‐assembly process by the number of 1, 8‐naphthalimide groups in the gelator

AbstractThree naphthalimide‐based gelators (NE1,NE2, NE3) with corresponding one, two and three N‐undecanoic acid methylester‐1,8‐naphthalimide were designed and synthesized (the abbreviation NE1‐NE3, N assigned to the naphthalimide, E assigned to ester, and numerber representing the number of N‐undecanoic acid methylester‐1,8‐naphthalimide) The different number of 1, 8‐naphthalimide groups in gelator endowed them with the different central groups, conjugated structures and steric configurations, which could bring different self‐assembly abilities and behaivors. The self‐assembly processes of three gelators in different solvents were characterized by multiple characterization technologies. The gelation ability, self‐assembly structure, fluorescence emission behavior, material surface wettability of this system could be regulated by the number of 1, 8‐naphthalimide groups. Gelator NE1 possessed the best gelation ability among three gelators, and the self‐assembly structures in gels NE1 from different solvents were completely different from that of gels NE2 and NE3. In addition, surface wettability of film NE1 exhibited the highest hydrophobicity under the same condition. Fluorescence emission behavior of this system could be tuned by the number of 1, 8‐naphthalimide groups solvent and gel state. At the same condition, the absorbance at the same band was gradually decreased with the number of 1, 8‐naphthalimide groups increasing. This work will provide a new design way for construction of functional supramolecular self‐assembly process.

Advanced naphthalimide-based supramolecular fluorescent self-assembly approach for Fe3+ detection and applications

A facile low-molecular-weight gelator based on 1,8-naphthalimide derivative functionalized by 2-hydroxynaphthalene unit has been designed and synthesized. The gelator exhibited distinct fluorescence emission behavior in different organic solvents. Intriguingly, it could assemble into supramolecular solution aggregates and gel in DMF-H2O mixed solvents, as well as the gelation process showed fluorescence enhancement characteristic. The self-assembly mechanisms and structures of these states were thoroughly characterized by several technologies, and single crystal was proudly obtained to verify the self-assembly process. In addition, the solution aggregates and gel both showed superior selective and sensitive sensing property for Fe3+ with a fluorescence ‘‘turn-off’’ detection mechanism, and the detection limit was 7.58 × 10−8 M and 1.51 × 10−8 M, respectively. The sensing mechanism was thoroughly verified by spectral analysis and density functional theory (DFT) which was barely presented in the literatures. Furthermore, the solution aggregates were successfully applied in detecting Fe3+ in real water samples with satisfactory recoveries, as well as the gel-coated test strip could be used as a fluorescent display material.

Dansyl-labelled cellulose as dual-functional adsorbents for elimination and detection of mercury in aqueous solution via aggregation-induced emission

Dansyl chloride fluorophore exhibits typical aggregation induced fluorescence emission behavior in acetone/water solution. To realize the integration of detective and adsorptive functions, dansyl chloride is covalently immobilized on cellulose substrate to fabricate an efficient adsorbent for mercury ions in water. The as-prepared material exhibits excellent fluorescence sensing performance exclusively for Hg (II) with the presence of other metal ions. A sensitive and selective fluorescence quenching across the concentration range of 0.1–8.0 mg/L is observed with a detection limit of 8.33 × 10−9 M as a result of the inhibition of aggregation induced emission caused by the coordination between adsorbent and Hg (II). Besides, the adsorption properties for Hg (II) including the influence of initial concentration and contact time are investigated. Langmuir model and pseudo-second-order kinetics are demonstrated to fit well with the adsorption experiment for the uptake of Hg (II) by the functionalized adsorbent, also, intraparticle diffusion kinetic model is proved to aptly describe the Hg (II) removal in aqueous solution. In addition, the recognition mechanism is considered to originate from the Hg (II) triggered structural reversals of naphthalene ring units which are verified by the X-ray photoelectron spectroscopy and density functional theory calculation. Moreover, the synthesis method used in this work also provides a strategy for the sensing application of organic sensor molecules with AIE properties in which the aggregated behavior could be appropriately realized.

One-pot synthesis of fluorescent aminoclay and the ratiometric fluorescence detection of sunset yellow

Herein, a facile one-pot solvothermal strategy was utilized for fabrication of fluorescent aminoclay (F-AC) using MgCl2, 3-aminopropyltrimethoxysilane and m-phenylenediamine as precursors. This approach provides a simple approach for scale-up synthesis of F-AC. The as-prepared F-AC exhibited blue-green fluorescence and good photostability. And pH significantly affects the fluorescence emission behavior of F-AC, and F-AC showed the strongest fluorescence at pH = 4.0. The fabricated F-AC was utilized for ratiometric fluorescence determination of sunset yellow with good sensitivity by virtue of the ratiometric fluorescence varies at 535 nm and 490 nm, and a linear relationship in the range of 0–30 μM was obtained with a LOD of 0.195 μM. Furthermore, the F-AC was utilized for anti-counterfeiting and fabricated as fluorescent gel and membrane, revealing the promising optical applications of F-AC.

Facile Synthesis of Multi-Emission Nitrogen/Boron Co-Doped Carbon Dots from Lignin for Anti-Counterfeiting Printing.

The transformation of lignin with natural aromatic structure into value-added carbon dots (CDs) achieves a win-win situation for low-cost production of novel nanomaterials and reasonable disposal of biomass waste. However, it remains challenging to produce multi-emission CDs from biomass for advanced applications. Herein, a green and facile approach to preparing multi-emission CDs from alkali lignin via N and B co-doping is developed. The obtained N and B co-doped CDs (NB-CDs) show multi-emission fluorescence centers at 346, 428 and 514 nm under different excitations. As the doping amount of N and B increases, the fluorescence emission band gradually shifts to 428 and 514 nm, while that at 346 nm decreases. The fluorescence mechanism is explored through the research of the structure, composition and optical performance of NB-CDs in combination with density functional theory (DFT) calculations. It demonstrates that the effect of doping with B-containing functional groups on the fluorescence emission behavior is multivariate, which may be the crucial contribution to the unique multi-emission fluorescence of CDs. The multi-emission NB-CDs with prominent stability are applied for multilevel anti-counterfeiting printing. It provides a promising direction for the sustainable and advanced application of biomass-derived CDs, and the theoretical results highlight a new insight into the deep understanding of the multi-emission fluorescence mechanism.

Ultra-bright green carbon dots with excitation-independent fluorescence for bioimaging

Current and future diagnostics urgently need imaging agents that are non-toxic and superior to clinically used small molecule dyes. Herein, we have developed luminescent green light-emitting carbon dots (GCDs) via a single-step hydrothermal reaction using a low-cost chemical precursor, p-toluenesulfonic acid. The GCDs exhibit excitation-independent fluorescence (FL) emission with the photoluminescence quantum yield of 70% and no FL quenching up to 1.25 mg/mL. The GCDs exhibit negligible cytotoxicity up to 250 µg/mL concentration in RAW 264.7 cells. Interestingly, GCDs exhibit an excitation-independent and concentration-dependent fluorescence emission behaviour. In vitro, the peak emission was obtained at 520 nm using the excitation at 430 nm. Whereas FL intensity increased with increasing concentration up to 1.25 mg/mL and a sharp decrease in FL intensity is observed upon further increasing the concentration of GCDs. Upon subcutaneously injecting the GCDs into a euthanized mouse, a similar concentration-dependent FL behaviour is evident. Background autofluorescence hinders the use of the GCDs at 420 nm excitation, however, a strong FL emission at 520 nm can be obtained by exciting subcutaneously injected GCDs at 465 nm—demonstrating excitation-independent emission characteristics. The above results indicate the potential of the non-toxic, low-cost carbon dots for diverse bioimaging applications.Graphical abstractUltra-bright green-emitting carbon dots (GCDs) with photoluminescence quantum yield of 70% were synthesized using p-toluenesulfonic acid and ethylenediamine as precursors. The GCDs were subcutaneously injected into fresh mouse cadaver for fluorescence (FL)bioimaging, showing dose-dependent FL intensity behaviour.

DNA patterning utilizing mixed monolayer template by phase separation between hydrocarbons and fluorocarbons and evaluation of second-order structural maintenance ability

Adsorption of DNA molecules on mixed phase-separated monolayers composed of a hydrocarbon-containing comb copolymer with an s-triazine ring and a fluorinated s-triazine derivative and their fluorescence emission behavior were investigated. DNA molecules derived from salmon testes were selectively adsorbed only on the diamino-s-triazine ring of the hydrogenated copolymer in the monolayer from the subphase. A mixed monolayer of a hydrocarbon-based comb copolymer and an s-triazine derivative with fluorocarbons exhibited phase separation behavior on water surfaces and indicated expansion behavior, reflecting interactions on the subphase containing DNA molecules. The phase-separated morphology changed depending on the mixing ratio of the hydrogenated copolymer and fluorinated s-triazine derivative. After DNA adsorption, the height of the domain formed by the hydrocarbon chain was selectively increased. In addition, because the DNA molecules adsorbed on the phase-separated template film maintain their fluorescence emission ability, the second-order structure, which is the origin of the emission ability, was evaluated using circular dichroism spectroscopy. The phase-separated, template-adsorbed DNA molecules maintained the same positive Cotton effect as in solution and were predicted to retain exquisite and delicate steric structure, leading to functional occurrence.

Effects of elemental doping, acid treatment, and passivation on the fluorescence intensity and emission behavior of yellow fluorescence carbon dots

Hydrothermal methods are commonly used to synthesize carbon dots (CDs), but the synthesized CDs have the disadvantage of low quantum yields. In this paper, we used acid treatment, elemental doping, and passivation to treat the CDs, which could increase the quantum yield from 36% to 42%, 61% and 68%, respectively, and the doping and passivation treatments resulted in red-shifted and blue-shifted emission behavior of the CDs. The optical properties, morphology and chemical structure of CDs are analyzed to investigate the reasons for the quantum yield increase and the mechanism of excitation dependent emission (EDE) and excitation independent emission (EIE). The increase of quantum yield is mainly due to the increase of pyridine N content. The different optical behaviors depend mainly on the surface states of CDs. C–OH and C–O–C can create new energy levels leading to the appearance of EDE properties. C=O is an electron-absorbing group that weakens the conjugation effect leading to blue shift.