Structure-fluorescence Relationships Research Articles

Rhodamine 6G-PAH probes for heavy metal: Fluorescence detection, bioimaging, and solid-phase sensing application

Four rhodamine 6G-PAH probes with pyrene (R6G-Pyr), anthracene (R6G-Ant), acenaphthene (R6G-Acp) or phenanthrene (R6G-PA) as fluorophore were designed and synthesized for Hg(II) detection. Probe R6G-PA, which had the lowest detection limit of 0.84 nmol/L, displayed the best fluorescence performance as compared to the other three probes. This type of probe had good anti-interference properties against most common metal ions except Cu(II). Metal Cu(II) had a certain quenching effect on the fluorescence generated by Hg(II), with a minimum detection limit of 0.31 nmol/L (for R6G-Acp), indicating its potential practicability for Cu(II) detection. The structure-fluorescence relationship was discussed based on density functional theory (DFT) calculations, and R6G-PA + Hg(II), which had the minimum dihedral angle between polycyclic aromatic rings and rhodamine spiro ring, produced the strongest π-π accumulation and provided the brightest fluorescence. Probe R6G-PA was successfully employed for fluorescence detection of Hg(II) in biological samples. Its solid-phase sensor PS@R6G-PA was developed by immobilizing R6G-PA on PS microspheres for the determination of Hg(II) in water and food samples, with excellent reproducibility and fluorescence “on/off” response. The relative error of the spiked recovery rate was less than 10 %.

Tuning the emission of anti-rigidochromic fluorophore by alternating the polymer matrices for advanced data encryption

Anti-rigidochoromic fluorophores with bathochromic emission in rigidifying polymer matrix offer advantages such as high fluorescent contrast, broadly tunable emissions, and versatile stimuli-responsive behaviors. In this work, we systematically investigated the impact of polymer chemical structure on the emission of the anti-rigidochromic fluorophore. By precisely tuning intermolecular polar-π and π-π interactions between the polymer matrix and fluorophore, a range of emission colors could be achieved, spanning from deep blue (450 nm) to the yellow-orange region (600 nm). Notably, the emission of polymer/fluorophore composites can be precisely adjusted over temperature. Leveraging the distinctive features, we showcase advanced fluorescence encryption using the non-emissive polymers as an information carrier and the fluorophore as the decryption key, which efficiently addresses issues of conventional fluorophores such as photo-bleaching and low adhesive force. This work establishes the structure-fluorescence relationship for the anti-rigidochromic system and extends its application for advanced data encryption with a high level of security.

Designing a Mitochondria-Targeted Theranostic Cyclometalated Iridium(III) Complex: Overcoming Cisplatin Resistance and Inhibiting Tumor Metastasis through Necroptosis and Immune Response.

To develop a potential theranostic metal agent to reverse the resistance of cancer cells to cisplatin and effectively inhibit tumor growth and metastasis, we proposed to design a cyclometalated iridium (Ir) complex based on the properties of the tumor environment (TME). To the end, we designed and synthesized a series of Ir(III) 2-hydroxy-1-naphthaldehyde thiosemicarbazone complexes by modifying the hydrogen atom(s) of the N-3 position of 2-hydroxy-1-naphthaldehyde thiosemicarbazone compounds and the structure of cyclometalated Ir(III) dimers and then investigated their structure-activity and structure-fluorescence relationships to obtain an Ir(III) complex (Ir5) with remarkable fluorescence and cytotoxicity to cancer cells. Ir5 not only possesses mitochondria-targeted properties but also overcomes cisplatin resistance and effectively inhibits tumor growth and metastasis in vivo. Besides, we confirmed the anticancer mechanisms of Ir5 acting on different components in the TME: directly killing liver cancer cells by inducing necroptosis and activating the necroptosis-related immune response.

Optimization of nitrofuranyl calanolides for the fluorescent detection of Mycobacterium tuberculosis

Tuberculosis is a chronic lethal infectious disease caused by a single pathogen, Mycobacterium tuberculosis (Mtb). Previous studies developed nitrofuranyl calanolide (NFC) compounds as new class of Mtb diagnostic reagent, such as NFC-Tre-5. Through structure-fluorescence relationships (SFR) investigation, in this article, a new fluorescent probe, 3-vinylcoumarin (17a) with a 20-fold increase in the fluorescent fold change (FFC) value, was gained. Taking the advantage of specific trehalose metabolic mechanism of Mtb, 17a was further cooperated with a trehalose motif through modification of 4-propyl group to obtain 17a-Tre. The 17a-Tre could label the live infected mycobacteria in signal murine macrophage such as M. smeg, specifically mark the living Mtb in single cell from other typical species of bacteria, and detect the Mtb cells under microscope from the sputum of patients.

Synthesis of novel triazine-quinoline-appended naphthalimide sensors for Hg(II) recognition and their structure-activity relationship

Constructing intelligent molecules for specific recognition of metal ions is critically important in environmental and biological fields. In this work, three novel triazine-quinoline-appended naphthalimide fluorescent sensors (NAK1, NAK2, NAK3) with different lengths of the linker were constructed. Research concerning the structure-fluorescence relationships of the three compounds showed that they exhibited distinct photophysical properties in either solution state or solid state. Compound NAK2, containing triazine-quinoline group with an ethylene (-CH2CH2-) linker, showed the strongest liquid state fluorescence emission, and it also displayed superior recognitive selectivity and sensitivity to Hg2+. NAK2 could detect Hg2+ within 2 min in phosphate buffer (PBS)/EtOH (v/v, 3/2) with low detection limit (0.045 μmol/L), being applied in Hg2+ detection in environmental water samples. Job's plot, 1H NMR and DFT calculations demonstrate that NAK2 combined with Hg2+ in 1:1 because of the special coordination holes, causing the change of planarity and electron transfer. This new type of molecular switch provides a new way of building high-performance fluorescence sensors.

Structure-fluorescence relationships in pyrrole appended o-carborane crystalline materials

Based on three rationally designed pyrrole-appended o-carborane derivatives, we present that fluorescence properties of crystalline materials are highly dependent on intermolecular interaction and steric hinderance. Though the three molecules are similar in structure, single crystals of the three compounds showed obvious difference in molecular stacking and fluorescence behavior. Systematic studies indicate that fluorescence quantum yields, thermo-response as well as mechano-response are highly dependent on intermolecular interaction and steric hindrance. In the three crystalline materials, the CB-NMe crystals with weaker intermolecular interaction and looser molecular packing showed superior fluorescence quantum yield and temperature sensitivity. Accordingly, surface temperature detection strip with favorable reversibility is prepared by doping CB-NMe into the polymer. In addition, the CB-NMe aggregates can be used for monitoring bovine serum albumin (BSA) denaturation, as temperature response of the aggregates can be reversed when co-assembled with BSA.

Modulation of charge transfer and π-π interaction toward tunable fluorescence emission in binary cocrystals composed of carbazole derivatives and 1,2,4,5-tetracyanobenzene

Herein, with the targeted aim of constructing binary complex with tunable fluorescence emission, a series of novel charge transfer (CT) cocrystal C1–C4 are designed and synthesized via facile solution-processing approach by selecting carbazole derivatives 9-(4-bromophenyl)carbazole (BrCz), N-methylcabazole (MeCz), 1,4-di (carbazole-9-yl)benzene (DCB), 5,7-dihydro-7,7-dimethylindeno [2,1-b]carbazole (InCz) as donors (D) and 1,2,4,5-tetracyanobenzene (TCNB) as acceptor (A). The π-conjugation property and configuration factor of donors are considered to regulate the CT driving force and π-π interaction within cocrystals. Structural and optical analysis, as well as theoretical calculations are accomplished to investigate the as-resulting products. As expected, donor's larger π-moiety accompanied with lower ionization potential (IP) value and planar configuration that promotes to stronger π-π interaction, are beneficial to enhance CT degree, thus endowing corresponding cocrystals with longer emission wavelength. Therefore, C1–C4 realize tailorable fluorescence emission with donor-dependent features covering a wide range from 582 nm to 642 nm. The investigation not only provides a platform to understand the structure-fluorescence relationship, but also gives instructions to readily achieve tunable emission behavior by selecting suitable D/A individual component via CT cocrystal method.

Quantitative assessment of rhodamine spectra

With the development of single-molecule detection and super-resolution fluorescence imaging, rhodamine dyes gain new life. Through the modification of the N-substituents and the replacement of the oxygen atom in xanthene, the wavelength and brightness can be effectively changed. However, the spectra of rhodamine, especially due to the balance between ring-closed non-fluorescent lactone and ring-opened fluorescent zwitterion/cation, are sensitive to interference from various environmental factors. In this way, the spectral data of various rhodamines reported by different research groups under different test conditions lacked comparability, sometimes even lacked accuracy. In order to meet the requirements for the accuracy and uniformity of spectral data in the research of single molecule imaging and dye structure-fluorescence relationship study, we have tested the spectra of fifteen rhodamine dyes that cover the visible and near-infrared regions under exactly the same conditions. By studying the dependence of the spectra on dye concentrations, it was confirmed that 1 μmol/L was ideal for detection less from the interference of dye molecule aggregation. We provide comprehensive and reliable spectral data of these fifteen dyes, which are expected to be used as references for future research. And the direct comparison of different rhodamine spectra would help to understand the structure-fluorescence relationship of rhodamines.

Systematic study of synthesizing various heteroatom-substituted rhodamines from diaryl ether analogues.

The dye rhodamine, as the most popular scaffold to construct fluorescent labels and probes, has been explored extensively on its structure-fluorescence relationships. Particularly, the replacement of the oxygen atom in the 10th position with heteroatoms obtained various new rhodamines with improved photophysical properties, such as brightness, photostability, red-shifted emission and fluorogenicity. However, the applications of heteroatom-substituted rhodamines have been hindered by difficult synthetic routes. Herein, we explored the condensation strategy of diaryl ether analogues and o-tolualdehyde to synthesize various heteroatom-substituted rhodamines. We found that the electron property and steric effect in the rhodamine 10th position determined the synthetic yield. It's concluded that this condensation method was more suitable for the synthesis of heteroatom-substituted rhodamines with small or electron-donating groups like rhodamine, S-rhodamine and Si-rhodamine. We hope these results will benefit the design and synthesis of heteroatom-substituted rhodamines.

Synthesis, structure-fluorescence relationships and density functional theory studies of novel naphthalimide-piperazine-pyridine-based polystyrene sensors for Hg(ii) detection.

Two novel naphthalimide–piperazine–pyridine-based polystyrene solid-phase fluorescent sensors PS-NA and PS-ND with different lengths of the linker were synthesized and shown to be able to detect Hg(ii) ions. Their structures were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis. Fluorescence properties, including response time, pH effects, fluorescence titration, metal ion selectivity and regeneration, were investigated and compared. Sensor PS-NA displayed a higher fluorescence response to Hg(ii) than PS-ND, with a lower detection limit of 1.01 μM. The detection mechanism involving the Hg(ii) chelation-induced photo-induced electron transfer (PET) was proposed with the aid of density functional theory (DFT) calculations. Sensors PS-NA and PS-ND with seven other similar sensors from our previous studies were collected together for thorough structure–fluorescence relationship (SFR) studies. Sensor PS-NA being recyclable and environmentally friendly was successfully employed in the fluorescence detection of Hg(ii) in real water samples, indicating its good potential in practical application.

Fluorescence Enhancement of Aromatic Macrocycles by Lowering Excited Singlet State Energies.

A series of cyclo-meta-phenylene congeners with a variation of interphenylene bridges was synthesized by adopting concise synthetic routes to investigate the structure-fluorescence relationships of macrocycles. With fundamental UV-vis absorption and fluorescence spectra, no unique effect of the macrocyclic structures was noted. However, the fluorescence quantum yields were dramatically affected by the macrocyclic structures and varied at a range of 5-92%. The quantum yields qualitatively depended on the number of the vinylene-bridged phenanthrenylene panels, and the theoretical investigations revealed the energetic and structural effects of the phenanthrenylene panels during nanosecond photodynamic processes. A high energy barrier along the S0/S1 internal conversion path to reach the minimum energy conical intersection was necessary to hamper a nonradiative process, and with the transition state energy level of the excited singlet state being insensitive to macrocyclic structures, a low energy level of excited singlet states (S1MIN) was required to facilitate efficient fluorescence.

Structure-fluorescence relationship of push-pull 2-phenylbenzothiazole derivatives designed based on the firefly light-emitter

6-Dimethylamino-2-phenylbenzothiazole (1a) mimicking the firefly oxyluciferin structure and the derivatives with an electron-withdrawing substituent on the phenyl group were prepared, and their fluorescence properties were investigated in various solvents. 1a showed solvatochromic fluorescence with good fluorescence quantum yields (Φf >0.8). The introduction of an electron-withdrawing group led to a red-shift of the emission maximum. In particular, the derivatives with the 2,2-dicyanoethenyl and (1,3-dihydro-1,3-dioxo-2H-inden-2-ylidene)methyl groups showed near-infrared fluorescence in chloroform. In addition, the derivative with the phenylimine moiety showed efficient solid-state fluorescence, resulted from a molecular arrangement inhibiting intermolecular interactions for quenching the fluorescence state in crystals.

Divergent Synthesis of Dihydroxanthene-Hemicyanine Fused Near-Infrared Fluorophores through the Late-Stage Amination of a Bifunctional Precursor.

A late-stage amination of a bifunctional dihydroxanthene (DHX) scaffold is reported to access a wide variety of new near-infrared (NIR) chromophores/fluorophores. The divergent approach allows the coupling of aliphatic and aromatic amines and readily provides molecular diversity shedding light on the structure-fluorescence relationship of this emerging class of NIR fluorophores.

Fluorescent Gold Nanoclusters with Interlocked Staples and a Fully Thiolate‐Bound Kernel

The structural features that render gold nanoclusters intrinsically fluorescent are currently not well understood. To address this issue, highly fluorescent gold nanoclusters have to be synthesized, and their structures must be determined. We herein report the synthesis of three fluorescent Au24 (SR)20 nanoclusters (R=C2 H4 Ph, CH2 Ph, or CH2 C6 H4 (t) Bu). According to UV/Vis/NIR, differential pulse voltammetry (DPV), and X-ray absorption fine structure (XAFS) analysis, these three nanoclusters adopt similar structures that feature a bi-tetrahedral Au8 kernel protected by four tetrameric Au4 (SR)5 motifs. At least two structural features are responsible for the unusual fluorescence of the Au24 (SR)20 nanoclusters: Two pairs of interlocked Au4 (SR)5 staples reduce the vibration loss, and the interactions between the kernel and the thiolate motifs enhance electron transfer from the ligand to the kernel moiety through the Au-S bonds, thereby enhancing the fluorescence. This work provides some clarification of the structure-fluorescence relationship of such clusters.

Structure-fluorescence relationship: interplay of non-covalent interactions in homologous 1,3,5-triaryl-2-pyrazolines

A series of new homologous 1,3,5-triaryl-2-pyrazolines have been synthesized to understand the interplay of non-covalent interactions in the context of a structure-fluorescence relationship.

Study and Application of the Structure-Fluorescence Relationship of Naphthyridine-Containing Compounds

Amino-2-aryl-3H-chromeno(4,3,2-de)(1,6)naphthyridine-4-carbonitriles and 5-amino-2-aryl-3H-quinolino(4,3,2-de) (1,6)naphthyridine-4-carbonitriles were synthesized via literature method. The effect of the number of the fused ring, the amount of fluorescent auxochrome and the types of substituents on the luminescent properties of the products was investigated in detail to explore the relationships between their structure and luminescence properties. In the guidance of the structure- luminescence relationship, compound 4 was used as sensor to identify nine metal ions successfully. The products with potential researching and development value as organic fluorescent material were picked up.

Chemistry at Boron: Synthesis and Properties of Red to Near-IR Fluorescent Dyes Based on Boron-Substituted Diisoindolomethene Frameworks

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications.

New fluorescent compounds for plastic scintillator applications

The fluorescent compound 3-hydroxyflavone (3HF) has been modified in order to study the resulting structure-fluorescence relationship. A series of twelve derivatives, bearing different substituents at various positions on the phenyl ring, has been synthesized. Each derivative has been tested as a dopant for plastic scintillator applications by incorporating it in a polystyrene matrix. The absorption, fluorescence, and scintillation light yield characteristics of these compounds in polystyrene have been determined. In addition, emission time distributions have been measured and decay time constants have been calculated from these data.

Fluorescence properties of angiotensin II analogues in receptor-simulating environments: relationship between tyrosinate fluorescence lifetime and biological activity

Nanosecond time-resolved decays from excited-state tyrosinate fluorescence of angiotensin II analogues were measured from the emission at 350 nm. Fluorescence lifetimes were determined in several different solvents using N-acetyltyrosinamide as the reference standard. Long-lifetime tyrosinate fluorescence (LTF) of angiotensin II (ANG II) was observed in propylene glycol, trifluoroethanol and isopropanol but not in DMSO or water. The addition of SDS at a concentration sufficient to induce micelle formation in water resulted in LTF for ANG II. LTF for ANG II was longer in propylene glycol (21 ns) than in isopropanol (16 ns) whereas the % conformer(s) producing LTF was higher in isopropanol (79%) than in propylene glycol (19%). For a series of ten angiotensin analogues, LTF values determined in propylene glycol and isopropanol were a reflection of the contractile activities of these analogues in the rat uterus assay. In propylene glycol, with the notable exception of ANG III, biologically active analogues had longer LTFs (13–21 ns) than inactive analogues (0–11 ns). In isopropanol, strong agonists had longer LTFs (13–16 ns) than weak agonists/inactive analogues (0–11 ns). Structure-fluorescence relationships suggest that the primary TyrOH acceptor in ANG II is the His 6 imidazole group, and that the C-terminal car☐ylate has an essential auxiliary role in generating long-lived tyrosinate fluorescence. The present findings appear to support the proposition that the receptor conformation of ANG II contains a tripartite interaction of Tyr, His and car☐ylate groups which is analogous to that found at the active site of serine proteinases, and that the tyrosinate nucleophile may activate angiotensin receptors. Solvents of intermediate polarity such as propylene glycol and isopropanol appear to induce conformations for small peptides such as angiotensin which resemble those present at membrane receptors.

Stilbene Isothiocyanates as Potential Fluorescent Tagging Agents

Two groups of stilbene isothiocyanate derivatives, α-phenylcinnamic acids and α-phenylcinnamonitriles, have been synthesized. These compounds and their required intermediates were studied as to their structure-fluorescence relationships in an effort to develop a protein-tagging agent with blue fluorescence.