Fluorescence Quantum Yield Research Articles

Hyperspectral Indices Developed from Fractional-Order Derivative Spectra Improved Estimation of Leaf Chlorophyll Fluorescence Parameters.

Chlorophyll fluorescence (ChlF) parameters offer valuable insights into quantifying energy transfer and allocation at the photosystem level. However, tracking their variation based on reflectance spectral information remains challenging for large-scale remote sensing applications and ecological modeling. Spectral preprocessing methods, such as fractional-order derivatives (FODs), have been demonstrated to have advantages in highlighting spectral features. In this study, we developed and assessed the ability of novel spectral indices derived from FOD spectra and other spectral transformations to retrieve the ChlF parameters of various species and leaf groups. The results obtained showed that the empirical spectral indices were of low reliability in estimating the ChlF parameters. In contrast, the indices developed from low-order FOD spectra demonstrated a significant improvement in estimation. Furthermore, the incorporation of species specificity enhanced the tracking of the non-photochemical quenching (NPQ) of sunlit leaves (R2 = 0.61, r = 0.79, RMSE = 0.15, MAE = 0.13), the fraction of PSII open centers (qL) of shaded leaves (R2 = 0.50, r = 0.71, RMSE = 0.09, MAE = 0.08), and the fluorescence quantum yield (ΦF) of shaded leaves (R2 = 0.71, r = 0.85, RMSE = 0.002, MAE = 0.001). Our study demonstrates the potential of FOD spectra in capturing variations in ChlF parameters. Nevertheless, given the complexity and sensitivity of ChlF parameters, it is prudent to exercise caution when utilizing spectral indices for tracking them.

Synthesis and Properties of a Strained Triple Nanohoop.

A strained triple nanohoop with a shared central benzene unit is synthesized using a threefold intramolecular ring-closing approach. Among the five possible constitutional isomers, the isomer with the highest D3h symmetry is isolated, the structure of which contains three nanohoop blades and a central hexaphenylbenzene unit. The structure is elucidated using NMR spectroscopy and mass spectrometry. The optical and electrochemical properties are investigated, revealing a moderate fluorescence quantum yield of 40 %. A water-soluble nanomaterial is prepared using a nanoparticle encapsulation method, and a fluorescence quantum yield of 10 % is retained, which demonstrates the potential of the nanomaterial in biological systems.

Self-Internal Standard Fluorescence for Ultrasensitive Detecting of mtDNA to Evaluate Matrilineal Genetic Defect Levels.

Mitochondrial DNA (mtDNA) is a unique genetic material characterized by maternal inheritance. It possesses a circular structure devoid of histone protection and exhibits low cellular abundance, which poses great challenges for its sensitive and selective detection at the living cell level. Herein, we have designed three bis-naphthylimide probes with varying linker lengths (NANn-OH, n = 0, 2, 6), facilitating the formation of distinct twisted or folded molecular conformations in the free state. These probes emit the red fluorescence around 627 nm with different fluorescence quantum yields (ΦNAN0-OH = 0.0016, ΦNAN2-OH = 0.0136, and ΦNAN6-OH = 0.0125). When encountering mtDNA (0.4-3.4 μg/mL), these probes undergo conformational changes depending on the length of the attached C-strand and exhibit a gradually increasing fluorescence signal around 453 nm. The fluorescence intensity increased to 13.5-fold, 1.9-fold, and 8.2-fold, respectively. Notably, the red fluorescence intensities around 627 nm remain constant throughout this process, thus serving as an inherent correction mechanism for proportional fluorescence signal enhancement to improve selectivity and sensitivity. NAN0-OH, NAN2-OH, and NAN6-OH showed good linearity for mtDNA in the range of 0.4-3.4 μg/mL with detection limits of LODNAN0-OH = 1.04 μg/mL, LODNAN2-OH = 1.10 μg/mL, and LODNAN6-OH = 1.15 μg/mL. Cellular experiments reveal that NAN6-OH effectively monitors curcumin-induced mtDNA damage in HepG-2 cells while enabling monitoring of genetic mtDNA damage. We anticipate that this tool holds significant potential for the precise evaluation of maternal genetic defects, thereby enhancing hypersensitive assessment in clinical medicine.

Alfalfa biomass as a green source for the synthesis of N,S-CDs via microwave treatment. Application as a nano sensor for nifuroxazide in formulations and gastric juice

BackgroundResearchers have investigated different techniques for synthesis of carbon dots. These techniques include Arc discharge, laser ablation, oxidation, water/solvothermal, and chemical vapor deposition. However, these techniques suffer from some limitations like the utilization of gaseous charged particles, high current, high temperature, potent oxidizing agents, non-environmentally friendly carbon sources, and the generation of uneven particle size. Therefore, there was a significant demand for the adoption of a new technology that combines the environmentally friendly aspects of both bio-based carbon sourcing and synthesis technique. ResultsMedicago sativa L (alfalfa)-derived N, S-CDs have been successfully synthesized via microwave irradiation. The N,S-CDs exhibit strong fluorescence (λex/em of 320/420 nm) with fluorescence quantum yield of 2.2 % and high-water solubility. The produced N,S-CDs were characterized using TEM, EDX, Zeta potential analysis, IR, UV–Visible, and fluorescence spectroscopy. The average diameter of the produced N, S-CDs was 4.01 ± 1.2 nm, and the Zeta potential was −24.5 ± 6.63 mv. The stability of the produced nano sensors was also confirmed over wide pH range, long time, and in presence of different ions. The synthesized N, S-CDs were employed to quantify the antibacterial drug, nifuroxazide (NFZ), by fluorescence quenching via inner filter effect mechanism. The method was linear with NFZ concentration ranging from 1.0 to 30.0 μM. LOD and LOQ were 0.16 and 0.49 μM, respectively. The method was applied to quantify NFZ in simulated gastric juice (SGJ) with % recovery 99.59 ± 1.4 in addition to pharmaceutical dosage forms with % recovery 98.75 ± 0.61 for Antinal Capsules® and 100.63 ± 1.54 for Antinal suspension®. The Method validation was performed in compliance with the criteria outlined by ICH. Significance and noveltyThe suggested approach primarily centers on the first-time use of alfalfa, an ecologically sustainable source of dopped-CDs, and a cost-effective synthesis technique via microwave irradiation, which is characterized by low energy consumption, minimized reaction time, and the ability to control the size of the produced CDs. This is in line with the growing global recognition of the implementation of green analytical chemistry principles.

The controllable synthesis of multi-color carbon quantum dots modified by polythiophene and their application in fluorescence detection of Au3+ and Hg2+

Herein, hydrothermal method was used to prepare a series of multi-color polythiophene modified carbon quantum dots. Under UV excitation, fluorescence their maximum emission wavelengths appear at 612 nm, 570 nm, and 540 nm respectively. The prepared CD-BTH and CD-BN can have specific detection of Au3+ and Hg2+ through fluorescence quenching effect. The detection limits for Au3+ are 3 nM and 5.4 nM respectively, and for Hg2+ are 23 nM and 90 nM respectively. CD-KN detects Au3+ specifically through fluorescence resonance, with a detection limit of 33 nM. Under the interference of other metal ions, three types of polythiophene modified quantum carbon dots exhibit excellent selectivity for the responsive ions. Meanwhile, this article also elucidates the law that as the electron withdrawing ability of the side chains of polythiophene derivatives increasing, the fluorescence emission peaks of the prepared polythiophene modified carbon dots shifts red and the fluorescence quantum yield is higher.

Photophysical mechanism study of photophysical properties of new red BODIPY chromophores with or without methyl substitution

The relationship between the photophysical properties and structure of BODIPY derivatives always has attracted much attention. Two new BODIPY derivative chromophores with phenyl group substitutions at meso-/6- positions, with or without methyl substitutions at 1/3/5/7 positions were investigated by ways of combination of multiple experimental techniques and theoretical methods. The chromophore without methyl substitutions has a larger Stokes shift and better viscosity sensitivity compared to the other one. The intrinsic reason is that considerable charge transfer between the BODIPY core and the 6- position group is achieved in chromophore. However, this charge transfer process is severely weakened, if 1-/3-/5-/7- methyl substitutions existing, via restricting rotation between the core and side groups. At the same time, the non-radiative process is amplified significantly in chromophore without methyl substitution and the fluorescence efficiency decrease from 51.7% (with methyl substitutions) to 1.84% (without methyl substitutions) in DMSO. Quantum calculations indicate the presence or absence of methyl substitution can change both the shape and height of the torsional potential energy curve of the side groups, thereby affecting the fluorescence quantum yield and viscosity response performance of chromophores. Our work can provide foundation and ideas for designing and optimizing BODIPY derivatives with objective photophysical properties.

“Crossbreeding” NIR‐II flavchromene for PSMA‐positive prostate cancer detection and image‐guided surgery

AbstractProstate‐specific membrane antigen (PSMA) is known to be overexpressed in prostate cancer (PCa). The development of precise and rapid imaging technologies to monitor PSMA is crucial for early diagnosis and therapy. Fluorescence imaging in the second near‐infrared window (NIR‐II) has emerged as a powerful tool for real‐time tracking and in vivo visualization, offering high sensitivity and resolution. However, there is a lack of stable, bright and easy‐to‐implement NIR‐II fluorescent probes for PSMA targeting. Herein, we presented a PSMA‐targeting NIR‐II fluorescent probe FC‐PSMA based on π‐conjugated crossbreeding dyed strategy that affords high stability, large extinction coefficient, and good brightness. As demonstrated, FC‐PSMA displayed a high fluorescence quantum yield in fetal bovine serum (FBS). Following intravenous injection of FC‐PSMA, the tumor‐to‐normal ratio of fluorescence intensity steadily increased over time, reaching a peak at 48 h (tumor‐to‐leg ratio = 12.16 ± 0.90). This advancement enables precise identification of PC through NIR‐II fluorescence imaging, facilitating high‐performance guidance for prostate cancer resection surgery.

Molecularly engineered high-performance AIE luminogen for NIR-III excitable deep-brain three-photon fluorescence imaging

Three-photon microscopy (3PM) utilizing near-infrared-III (NIR-III) excitation has emerged as an effective technology for deep-tissue bioimaging. Within this domain, organic small molecules with aggregation-induced emission (AIE) property prove to be promising candidates as high-quality 3PM imaging agents because of their exceptional optical properties and the general merit of biocompatibility that most organic small molecules possess. However, due to the bidirectional effects of the intrinsic structure distortion of AIE luminogens (AIEgens) on the three-photon absorption cross section (σ3) and fluorescence quantum yield (η), two crucial factors that determine 3PM performances, the development of high-powered AIE-active 3PM probes with robust ησ3 remains a formidable challenge. In this work, by synergistically integrating multiple beneficial principles into the molecule design, an innovative AIE-active 3PM probe with a symmetrical quadrupole D–A–D architecture, namely TIT, was successfully constructed. Owing to the harmonized planarity and distortion, as well as strong D–A interaction within TIT, the as-prepared TIT nanoparticles (NPs) exhibited boosted ησ3 under 1665 nm NIR-III excitation. This breakthrough enabled brain vascular imaging at a remarkable depth of 1895 μm after craniotomy, thus positioning TIT among the top three organic 3PM probes in terms of imaging depth. In addition, successful hemodynamic imaging at a depth of 1200 μm within the mouse brain post-craniotomy was also accomplished. These achievements establish TIT NPs as highly promising probes for in vivo deep-brain three-photon imaging.

Investigation on the Influence of Solvents Environment on the Optoelectronic Properties of the Fluorescent Probe 1,3,4-Oxadiazole Analogues: A Combined Theoretical and Experimental Study.

This study investigates the photophysical properties of a nitrobenzene-substituted 1,3,4-oxadiazole derivative (OX-NO) using both theoretical and experimental methods. The impact of the solvent on OX-NO absorption and fluorescence spectra, as well as its fluorescence quantum yield, was initially studied. A noticeable bathochromic shift in the Stokes shift indicated a π→ π* transition within the molecules. Solute-solvent interactions were analysed using Catalan parameters, distinguishing between specific and nonspecific interactions. Excited state dipole moments were derived from Lippert's, Bakshiev's, and Chamma Viallet's equations, showing increased polarity in the excited state compared to the ground state. Ground state dipole moments were determined via solvatochromic shift methods and ab initio techniques. Additionally, detailed analyses of bond length, angles, dihedral angles, Mulliken charge distribution, and HOMO-LUMO energy gap were conducted using the DFT-B3LYP-6-311G basis set in Gaussian-09W. The energy band gap values obtained from theoretical calculations and experimental methods (cyclic voltammetry and UV-Visible spectroscopy) exhibited excellent agreement. Reactive sites such as electrophilic and nucleophilic regions were identified through total electron density, electrostatic maps, molecular electrostatic potential, and 3D plots using DFT computational analysis. Global descriptors were employed to characterize the compounds' chemical reactivity comprehensively. The observed photophysical attributes underscore the potential of these fluorophores in various applications like organic light-emitting diodes, solar cells, and chemosensors. This study contributes crucial insights into the optoelectronic properties of nitrobenzene-substituted 1,3,4-oxadiazole derivatives, paving the way for their future integration in advanced technological domains.

Carbon dots with tunable excitation-independent fluorescence and organelle-specific targeting via core graphitization and surface groups engineering

Single-emission fluorescence and non-specific cellular organelle-targeting limit the application of carbon dots (CDs) in bio-imaging. Here, we proposed an adjustable strategy for synthesis of four CDs: Tm1-, Tm2-, Tma-, and Tp-CDs. The synthetic scheme was designed with tartaric acid and m-/p-phenylenediamine as precursors and water/acetone as solvent through hydrothermal/solvothermal synthesis and (or) column chromatography isolation. The maximum productivity of the CDs was 56.2 % and the highest fluorescence quantum yield was 47.8 %. These CDs emitted excitation-independent blue, green, and yellow fluorescence, respectively. The red shift of CDs fluorescence was caused by increasing graphitized conjugated sp2 domain and graphitic nitrogen content of carbon core. The hydrophilicity/lipophilicity and protonation ability of CDs determined their cellular uptake, intracellular trafficking and subcellular targets, including endoplasmic reticulum, lysosomes and nucleus. These CDs have the potential application in fluorescence visualization of live bacteria and in the organelle-targeted imaging of living mammalian, fungal, and plant cells. The study provides novel insights into rational design of CDs with multi-color fluorescence and organelle-specific targeting in live cells.

Heavy-Atom-Free Triplet-Triplet Annihilation Upconversion in Photo-cross-linked Polymer Poly(ethylene glycol) Diacrylate.

Heavy-atom-free triplet-triplet annihilation (TTA) upconversion sensitized by a thermally activated delayed fluorescence (TADF) molecule is investigated in a dried gel made of a photo-cross-linked polymer as the solid-state matrix. The upconversion fluorescence quantum yields, ΦUC, of the solid-gel TTA system at different penetration depths are measured accurately based on a developed internal-reference method. It is found that ΦUC is greatest at the surface and then decreases exponentially with increasing depth, influenced by the substrate absorption. The same process is also performed in a TTA solution at different depths, but a completely different result is obtained; there is little difference for ΦUC. To the best of our knowledge, this is the first time the quantum yields at different transmission depths have been mentioned and calculated experimentally. These results illustrate the importance of accurately measuring the quantum yield of solid-phase TTA upconversion and provide a novel way to improve the solid-phase TTA quantum yield by reducing the thickness of the substrate.

Novel Dual-Emission Emitters Featuring Phenothiazine-S-Oxide and Phenothiazine-S,S-Dioxide Motifs.

In this study, we have successfully designed and synthesized two novel dual-emission emitters featuring phenothiazine-5-oxide and phenothiazine-5,5-dioxide motifs, characterized by highly lopsided and asymmetric conformational states. Through rigorous spectral examinations and DFT calculations, the compounds exhibit distinctive ICT phenomena, coupled with efficient emission in solid states and AIEE characteristics under high water fractions in DMF/H2O mixtures. These non-planar luminogens exhibit vibrant green and blue solid-state luminescence, with fluorescence quantum yields of 24.1 % and 15.21 %, respectively. Additionally, they both emit green fluorescence in THF solution, with notable emission quantum yields (QYs) 36.4 % and 30.4 %. Comprehensive theoretical investigations unveil well-defined electron cloud density separation between the energies of HOMO/LUMO levels within the two luminogens. Notably, the targeted molecule harboring the phenothiazine-S,S-dioxide motif also demonstrates remarkable reversible mechanofluorochromic properties. Moreover, we testify their potential in applications such as solid-state rewritable information storage and live-cell imaging in solution states. Through theoretical calculations and comparative studies, we have explored the intrinsic relationship between molecular structure and performance, effectively screening and identifying new fluorescent molecules exhibiting outstanding luminescent attributes. These discoveries establish a robust theoretical and technical foundation for the synthesis and application of efficient DSE-based MFC materials, opening new avenues in the realm of advanced luminescent materials.

Structural Fine-Tuning to Achieve Highly Fluorescent Organic and Water-Soluble Thiazolo[5,4-d]thiazole Chromophores.

Fluorescent molecular systems are important for various applications such as sensing of analytes, probes for biologically relevant processes and as optoelectronic materials. Achieving high fluorescence quantum yield across the spectrum of solvent polarity and in solid-state is challenging in molecular materials. Herein, we present a strategy to achieve strongly fluorescent molecular materials based on weak intramolecular charge-transfer (ICT) in a family of unsymmetrical donor-thiazolo[5,4-d]thiazole-acceptor systems (both neutral and cationic). Detailed photophysical studies reveal that the delicate balance between the donor and acceptor result in high solution-state fluorescence quantum yield (>80 %) in both polar protic and apolar solvents. Quantum chemical computations uncover a hitherto unappreciated insight that the extent of ICT is aptly represented by the change in Mulliken charges between the ground and excited state for different fragments rather than the classical approach of monitoring the change in dipole moment for the entire molecule. This insight rationalizes the observed photophysical properties and can have implications in the design of tuneable donor-π-acceptor systems.

Metal-enhanced fluorescence (MEF) effect based on silver nanoparticles with different UV spectra on a surface carbon dot-based novel dry platform

In this work, to enhance the fluorescence quantum yield of carbon dots (CDs), a novel metal-enhanced fluorescence (MEF) structure was designed by decorating CDs on silver nanoparticle (AgNPs) film. The glass slide-AgNPs (GS-AgNPs) structure was fabricated using the electrostatic adsorption method, and the AgNPs-CDs structures were prepared by the direct drying method, which then formed the GS-AgNPs-CDs composite structure. In this structure, the MEF effect was found to be size dependent by changing the 5 types of AgNPs with different sizes. And the MEF effect also decreased as the distance between the AgNPs and CDs increased by using polyvinylpyrrolidone (PVP) to separate the AgNPs and CDs. This hybrid structure can be used as a fluorescence detection platform and the recorded fluorescence intensity of GS-AgNPs 428 nm-CDs achieved a maximum enhancement factor (EF) of 31.72. Considering the high enhancement factor, this system may become promising to find potential applications in biochemical assay fields.

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.

Design and synthesis of fluorescent BODIPY derivatives with D-A structure for cancer cell imaging

Boron-dipyrromethene (BODIPY) as a traditional fluorescent dye has received increasing attention because of its high molar extinction coefficient, easy modification, and good light stability. In this work, three BODIPY compounds (BDP-1, BDP-2 and BDP-3) were designed and synthesized by introducing PEG chains and a naphthalimide (NI) group onto the parent structure of BODIPY. Due to the electron-withdrawing properties of NI, the compounds of BDP-2 and BDP-3 formed a typical donor (D)-acceptor (A) structure, which led to the red-shifted absorption and fluorescence spectrum. The synthesized BODIPY exhibited intense green emission, with fluorescence quantum yield of 0.66, 0.29, and 0.19 for BDP-1, BDP-2 and BDP-3 respectively. The decrease in fluorescence of BDP-2 and BDP-3 was probably ascribed to the enhanced intramolecular charge transfer because of the introduction of the NI group. The good biocompatibility and low cytotoxicity of the synthesized BODIPY compounds were verified by the CCK-8 assay. The subcellular localization of the three compounds was further evaluated through a confocal laser scanning microscope. The results showed that these BODIPY derivatives were mainly localized in the lysosomes of cancer cells. Thus, the synthesized BODIPY fluorescent dyes show promising applications in tumor imaging benefiting from their good biocompatibility and strong fluorescence.

Facile green synthesis of dual stabilized near-infrared CuInSe/ZnS quantum dots as fluorescent probes for cancer-bacteria imaging

Imaging is a critical step in diagnosis and therapy; thus, developing a non-carcinogenic near-infrared (NIR) emitting probe for guided therapy remains a priority for effective bacteria and cancer treatment. Herein, we report the effect of dual stabilization in producing NIR fluorescent CuInSe/ZnS quantum dots (QDs) and their use as imaging probes in cancer-bacteria therapy. The as-synthesised NIR QDs were stabilized using different combinations of hydrophilic dual capping agents, MPA-Gelatine, TGA-Gelatine, MPA-Citrate and TGA-Citrate. The optical characteristics of the prepared dual-stabilized CuInSe/ZnS QDs indicate that the material has high stability and fluorescence quantum yield. The dual stabilization resulted in varied emission positions as well as fluorescence intensity for the as-synthesized QDs. The cytotoxicity evaluation showed that cells treated with dual stabilised CuInSe/ZnS QDs displayed good cell viability against malignant fibrous histiocytoma-like (KM-Luc/GFP) cells, mouse colon carcinoma (C26) cells and mouse mammary carcinoma (FM3A-Luc) cells. It also showed high affinity to prostate and human adenocarcinoma cells with no indication of QDs uptake by normal prostate cells. The biofilm analysis showed that the QDs uptake was elevated in Staphylococcus aureus (Gram-positive bacteria) than in Escherichia coli (Gram-negative bacteria). The dual stabilized QDs remain a promising study as future fluorescence probes for early diagnosis and guided cancer therapy.

Syntheses and properties of imidazopyridine-based ionic liquids

We have synthesized imidazopyridine-type ionic liquids and evaluated their properties. [Cnimpy][Br] (n = 4, 6, 8, 10), in which an alkyl group was introduced at the N1 position of imidazo[1,2-a]pyridine, were all solid at room temperature. Exchange of the counteranions of [Cnimpy][Br] with N(CN)2− and FSI− gave the ionic liquids [Cnimpy][N(CN)2] and [Cnimpy][FSI] in the liquid state at room temperature. In particular, the DSC thermogram of [C10impy][FSI] showed a clear melting point at 22 °C. In [Cnimpy][TFSI], ionic liquids consisting of cations with short alkyl chain lengths (n = 4,6) were solids at room temperature, while those with long alkyl chain lengths (n = 8,10) were liquids. [Cnimpy][FSI] has lower viscosity than other anion-consisting ionic liquids which showed a liquid state at room temperature. [Cnimpy][FSI] has lower viscosity than other anion-containing ionic liquids. In particular, [C4impy][FSI], with its relatively short alkyl chain length, exhibited a viscosity of 101 mPa·s at 25 °C, which renders it suitable for practical applications. [C4impy] [FSI] (50 μM acetonitrile solution) showed fluorescence with maximum absorption at 336 nm. Its fluorescence wavelength was shorter than that of imidazo[1,2-a]pyridine, whereas its fluorescence quantum yield (ΦF 0.39) was higher. Therefore, it is expected to be used as a composite material by employing FRET with a substance that exhibits fluorescence in the visible region.

Protolytic equilibrium, light absorption and emission of 2,7-dinitro-4,5-dibromofluorescein and related dyes: Fluorescent indicators sensitive to hydrogen bonds of the solvent

This article reports on the spectral data and protolytic equilibria parameters of a series of fluorescein halogen and nitro-halogen derivatives in solution. Absorption spectra and dissociation constants of 2,7-dinitro-4,5-dibromofluorescein (also called eosin bluish or eosin B), 2,4,5,7-tetrabromofluorescein (eosin or eosin Y), 2,7-dichlorofluorescein, and 3′,4′,5′,6′-tetrachlorofluorescein are determined in DMSO. The state of the tautomeric equilibria of molecules and anions is discussed. The behavior of the nitro-bromo derivative in solution strongly differs from other dyes due to the pronounced influence of the NO2 groups in 2 and 7 positions. As a result, the lactone tautomer predominates not only for the neutral form, H2R, but even for the double-charged anion, R2–. This kind of chain-ring tautomerism is not typical for other dyes under study. The influence of the solvent’s nature on the fluorescent properties of this dye is also of special interest. Whereas the solvatochromism of the HR– form of this compound as well as of the R– ion of its methyl ester is of medium strength, the emission intensity dramatically changes from bright fluorescence in DMSO and other non-HBD solvents to very poor in alcohols and water. Thus, these two dyes join the group of previously studied fluorescein derivatives, the fluorescence quantum yield of which is sensitive to the hydrogen bonds of the medium.

Click generated photochromic naphthalenediimide-dithienylethene diad: Application in deciphering secret codes

Photochromic molecules with efficient fluorescence switching capability remain a core research interest among the scientific community for the application in security technologies and anti-counterfeiting measures. A dithienylethene-naphthalene diimide diad was designed and synthesized using Cu(I) catalysed click reaction between a fluorescent core substituted naphthalene diimide (cNDI) and photochromic dithienylethene (DTE) molecule, which demonstrated excellent photocyclization (ksolution = 0.0359 s−1, ksolid = 0.0122 s−1) and photocycloreversion (ksolution = 0.01737 s−1, ksolid = 0.00456 s−1) dynamics with high fluorescence quantum yield (5o ΦF = 0.39, PSS ΦF = 0.05). The fluorescence property of the molecule was switched ‘on-off’ by UV and visible light irradiation respectively via Förster resonance energy transfer (FRET) mechanism in solution state as well as in solid state, which was further corroborated with DFT studies. In view of efficient fluorescence switching behaviour and high fatigue resistance properties (25 cycles), the molecule was successfully applied in secret code encryption-decryption purposes using barcode demonstrating real-life applicability of the molecule in security technologies.