Strongly fluorescent dipyrrinones. Internal quenching

Yellow N,N′-carbonyl-bridged dipyrrinones can generally be prepared from dipyrrinones simply by reaction with N,N′-carbonyldiimidazole in the presence of a strong, non-nucleophilic base. They are typically intensely fluorescent, with fluorescent quantum yields approaching 1.0. In an effort to shift the excitation wavelength, and thus the fluorescence emissions, strongly to the red, we prepared bridged dipyrrinones conjugated with thiobarbituric acid and Meldrum’s acid substituents at C-9. Such conjugation causes the dipyrrinones to have a magenta color (absorption wavelength shifted from ∼400 nm of a typical dipyrrinone to ∼550 nm of the dipyrrinone conjugate). For comparison, we also prepared analogs with formyl, carboxyl, acrylate, and acetyl substituents at C-9. Unexpectedly and uniquely, the 9-CHO substituent caused the fluorescence quantum yield to drop to ∼10⁻³ while carboethoxy substituent exerted only a minor influence.     

Methoxyl-induced fluorescence quenching in N,N′-bridged 9H-dipyrrinones and an X-ray crystal structure

Strongly fluorescent dipyrrinones can be prepared by bridging the pyrrole and lactam nitrogens with a carbonyl group, from reaction with N,N′-carbonyldiimidazole in the presence of a strong, non-nucleophilic base. The yellow, N,N′-carbonyl-bridged dipyrrinones typically have fluorescent quantum yields (φ_F) approaching 1.0. Thus, in chloroform, N,N′-bridged 9H-dipyrrinones with β-alkyl substituents: 2,3-diethyl-7,8-dimethyl has φ_F = 0.90 (λ_em = 465 nm) and 2,3-dimethyl-7,8-dimethoxy has φ_F = 0.84 (λ_em = 482 nm). In contrast, 2,3-dimethoxy-7,8-dimethyl and 2,3,7,8-tetramethoxy show red-shifted λ_em but with strongly reduced φ_F: φ_F = 0.10 (λ_em = 511 nm) and 0.08 (λ_em = 511 nm), respectively. Methoxy substituents on the lactam, but not the pyrrole ring act to quench the fluorescence and shift the emission and excitation wavelengths bathochromically. The first X-ray crystal structure of an N,N′-carbonyl-bridged dipyrrinone was obtained from 7,8-dimethoxy-2,3-dimethyl-10H-dipyrrin-1-one. Correspondence: David A. Lightner, Department of Chemistry, University of Nevada, Reno, Nevada 89557-0020, USA.     

The synthesis of Ag-polypyrrole nanocomposite coated latex particles and their application as a fluorescent quenching agent

 Submicron-sized Ag-polypyrrole/poly(styrene-co-methacrylic acid) (Ag-PPy/P(St-co-MAA)) composite particles were fabricated via a redox reaction between pyrrole and AgNO₃ in the presence of P(St-co-MAA) soap-free latex. The products are characterized by transmission electron microscopy (TEM), electron diffraction spectra (EDS), Raman spectra, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that Ag-PPy nanocomposites were in situ deposited onto the surface of P(St-co-MAA) latex particles tailored by carboxylic-acid groups. The nanocomposites of Ag-PPy distributed on the surface of polymer particles transformed from discretely dots to continuously coating as the reaction temperature increased from 15℃ to 60℃. Strawberry-like composite particles were obtained at the reaction temperature of 60℃. The TGA characterization confirmed that the Ag-PPy nanocomposites loading onto the P(St-co-MAA) particles were systematically controlled over a range of 6 wt%-42 wt% by changing the reaction temperatures. The fluorescence quenching effect of the Ag-PPy/P(St-co-MAA) composite particles was explored on Rhodamine B as a model molecule with the Stern-Völmer quenching constant K_SV of 5.9×10⁴ (g/mL)^-1. It is suggested that the fluorescence quenching effect is caused by the resonance energy transfer mechanism.     

Synthesis, Structure, and Fluorescence of Isomeric Indolizinediones. Carbonyl-Bridged Isodipyrrinones

Summary. In one-pot reactions, pyrrole-- and -aldehydes condense readily with 4-ethyl-3-methyl-3-pyrrolin-2-one to give isodipyrrinone analogs, which undergo intramolecular cyclization when the pyrrolealdehyde possesses an or -CO₂R group. The resulting regioisomeric pyrroloindolizinediones, with structures confirmed by NMR analysis, exhibit strong fluorescence, with quantum yields (_F) as high as 0.91 at _em450–550nm.     

α-Ketoacid Intermolecular Hydrogen Bonding. Supramolecular Ribbons and Stacking in α-Pyrroleglyoxylic Acids

Summary.  Rarely-seen carboxylic acid to ketone intermolecular hydrogen bonding is found in crystal structures of α-pyrroleglyoxylic acids. 3,4-Diethyl-1H-pyrrole-2-glyoxylic acid, prepared by saponfication of the reaction product between 3,4-diethylpyrrole and ethyl oxalyl chloride formed crystals that showed the uncommon carboxyl to ketone intermolecular hydrogen bonding, with the hydrogen-bonded α-pyrroleglyoxylic acids stacked neatly in layers. This α-ketoacid hydrogen-bonding pattern was repeated in (Z)-2,3,7,8-tetraethyl-10H-dipyrrin-1-one-9-glyoxylic acid, which also engaged in dipyrrinone-to-dipyrrinone intermolecular hydrogen bonding to form supramolecular ribbons in the crystal.     

Highly stable and fluorescent switching spirooxazines

Two novel photochromic spirooxazines, SO-NA1 and SO-NA2, containing a naphthalimide unit were synthesized. The imide group of naphthalimide unit is incorporated at the naphthoxazine fragment, thus giving strong electron-withdrawing effect favoring the long-lived merocyanine (MC) in the dark giving good colorability in solution. Remarkably, their open merocyanine (MC) forms exhibit significantly long lifetimes, almost three magnitudes longer than that of unsubstituted spironaphthoxazine (1). Moreover, the fluorescence of naphthalimide unit can be switched on and off by photoinduced conversion between the open and closed forms.     

Novel synthesis of meso-tetraarylporphyrins using CF3SO2Cl under aerobic oxidation

meso-Tetraarylporphyrins are synthesized from pyrrole and aryl aldehydes cleanly and efficiently in one pot at room temperature using equimolar amount of CF₃SO₂Cl in the presence of air as oxidant. By this novel method 5,10,15,20-tetraarylporphyrins can be prepared in excellent yields.     

Amphiphilic Dipyrrinones

Summary. Replacing the typical lactam β-alkyl substituents of xanthobilirubinic acid and kryptopyrromethenone, two bilirubin analogs long used as model compounds in studies of its photochemistry and metabolism, leads to increased amphiphilicity. Synthesized by base-catalyzed condensation of 3,4-dimethoxypyrrolin-2-one with the appropriate pyrrole α-aldehyde, the 2,3-dimethoxyl analogs of xanthobilirubinic acid and kryptopyrromethenone are yellow-colored dipyrrinones that form intermolecular hydrogen-bonded dimers in the solid, as determined by X-ray crystallography, and in CHCl₃, as revealed by ¹H NMR and vapor pressure osmometry. These two new dipyrrinones are approximately ten times more soluble in water than their parent dipyrrinones.     

Exciton Chirality. (A) Origins of and (B) Applications from Strongly Fluorescent Dipyrrinone Chromophores

Summary. (A) The origin of exciton interaction and examples of its application to organic stereochemistry are presented. (B) N,N-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration. N,N-Carbonylxanthobilirubic acid esters are strongly fluorescent, with a fluorescence quantum yield (_F) 0.8, but produce only weak exciton CD from the trans-1,2-cyclohexanediol template. The ester of an analog with benzoic acid replacing propionic, N,N-carbonyl-8-(4-carboxyphenyl)-3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one, exhibits strong fluorescence (_F=0.68, _em=493nm, _ex=422nm in CHCl₃) and UV-Vis absorption (21000 at 424nm) in organic solvents. Its diester with (1S,2S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (=+15dm³·mol^–1·cm^–1, =432nm; =–4dm³·mol^–1cm^–1, =380nm) that correlates with the Exciton Chirality Rule.     

N-acetylcysteine induced quenching of red fluorescent oligonucleotide-stabilized silver nanoclusters and the application in pharmaceutical detection

In this work, we reported a new, simple and sensitive method for determination of N-acetylcysteine (NAC) based on quenching of the red fluorescence of oligonuleotide-protected silver nanoculsters (Ag NCs) with the quantum yield of 68.3 ± 0.3%. This method was successfully used for the assay of NAC granules presenting a linear range from 100 nM to 1200 nM (LOD of 50 nM) with minimal interferences from potential coexisting substances. It is for the first time that quenching performance of the thiol-containing compound was found to follow a non-linear Stern–Volmer profile, indicative of a complicated quenching mechanism with static quenching dominating, in which DNA-template of Ag NCs was partly replaced by NAC, as elucidated by spectral investigations. This study extended the analytical application of silver nanoclusters as well as provided a more insightful understanding of the quenching mechanism of thiol-compounds on the fluorescence of Ag NCs.     

Structural studies of biarylpyridines fluorophores lead to the identification of promising long wavelength emitters for use in fluorescent chemosensors

Fluorescent chemosensors—molecules whose fluorescence emission changes in response to a reversible binding event—require both a substrate binding domain and a reporting fluorophore. Our approach to chemosensor development is based on a combination of a new signaling mechanism and a modular fluorophore synthesis. The latter feature has facilitated detailed study of the properties of polyarylpyridine fluorophores, and has led to the identification of a visibly-emissive pyridine as a promising lead structure for chemosensor development. The results of this study are described herein.     

Preparation of a novel composite particles and its application in the fluorescent detection of proteins

A new fluorescence method for the detection of proteins with novel composite nanoparticles (CdS/PPA) has been developed. The composite nanoparticles have been prepared through an in-situ polymerization method under ultrasonic irradiation. The surface of the composite nanoparticles was covered with functional groups (-COOH). These groups may play a major role in the improving the water solubility and biocompatibility of the nanoparticles. The composite particles is combined with proteins in NaAc-HCl buffer solution (pH=1.99), which can result in strong fluorescence, and the response is linearly proportional to the concentration of proteins. In λem/λex=650 nm/365 nm place (the stoke’ shift is 285 nm), its fluorescent strength reaches the maximum. Under the optimum conditions, the linear range is 0.10–20.0 μg·ml⁻¹ with the detection limit of 41 ng·ml⁻¹ for HSA, and 0.10–15.0 μg·ml⁻¹ with the detection limit of 35 ng·ml⁻¹ for Human γ-IgG . The method has been applied to the determination of the total protein in human serum samples collected from the hospital and the results are satisfactory.     

Control of charge transfer by conformational and electronic effects: Donor–donor and donor–acceptor phenyl pyrroles

Derivatives of N-pyrrolobenzene with a para-donor and a para-acceptor substituent on the benzene ring are compared. It is shown that by a suitable increase of the donor strength of the pyrrolo group, CT fluorescence can be achieved even for donor–donor-substituted benzenes. The ICT emission for sterically hindered compounds is more forbidden than that of unhindered phenyl pyrroles. This suggests conformational effects which induce a narrower twist angle distribution around a perpendicular minimum in the excited state.     

Synthesis,characterization and fluorescent properties of lanthanide complexes with two aryl amide ligands

Two aryl amide ligands, N-(p-tolyl)-2-(quinolin-8-yloxy)acetamide (L¹ ) and N-(4-chlorophenyl)-2-(quinolin-8-yloxy)acetamide (L² ), were synthesized. With these ligands, two series of lanthanide(III) complexes were prepared, Ln(L ⁿ )₂(NO₃)₃ (n = 1, 2; Ln = La, Sm, Eu, Gd, Dy), and characterized by the elemental analyses, molar conductivity, ¹H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of the complexes and the triplet state energies of the ligands were studied in detail. In addition, the quantum yields of both Eu(III) complexes and Eu(L⁰)₂(NO₃)₃ [where L⁰ is N-(phenyl)-2-(quinolin-8-yloxy)acetamide] 1 Wu, WN, Yuan, WB, Tang, N, Yang, RD, Yan, L and Xu, ZH. 2006. Spectrochim. Acta A, 65: 912[Crossref], [Web of Science ®] , [Google Scholar] were calculated. The results indicate that among the lowest triplet energies (T) of the three ligands, that of L² is most suitable to the resonance level (⁵D₁) of Eu(III) ion. Furthermore, Eu(L²)₂(NO₃)₃ has the highest fluorescence intensity and quantum yield of the three Eu(III) complexes.     

Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes

The synthesis and absorption/fluorescence properties of two novel intramolecular charge transfer (ICT) compounds of (fluorene-2-yl)-(9-ethylcarbazole-3-yl) ketene and 1-phenyl-3-(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2-pyrazoline were reported. The primary structure of the target compounds was characterized by IR and ¹H NMR. The systems contained a fluorenone or a propenon group as an electron acceptor (A) and an N-ethylcarbazole and a pyrazoline group as electron donors (D). From the emissive properties it was concluded that the electronic coupling between D and A was sufficient to allow charge transfer in these molecules. The ICT maximal emission displayed a large wavelength shift and Stokes shifts increased in response to the increase of the solvent polarity. The highly solvatochromic properties made the two compounds of great interest as new classes of fluorescent probes, electroluminescent and electrofax materials.     

荧光法猝灭测定木槿叶中混合氨基酸的总量

在乙酸-乙酸钠缓冲介质中,氨基酸能猝灭壳聚糖-茚三酮体系荧光,基于此,对木槿叶中混合氨基酸进行测定,并对该方法的测定条件进行了讨论.线性范围为0.5～3.0 mmol/L,检出限为0.1 mmol/L.木槿叶干粉中游离氨基酸的质量分数为10.18%,相对标准偏差为1.3%,回收率为102.5%～94.3%.     

Synthesis and photophysical behavior of thia-aza macrocycles with 9-anthracenylmethyl moiety as fluorescent appendage

1,3-Bis(bromomethyl)-2-methoxy-5-methylbenzene, 1,3-bis(bromomethyl)-2,4,6-trimethylbenzene, 1,3- and 1,4-bis(bromomethyl)benzene undergo nucleophilic substitution with methyl mercaptoacetate to provide respective diesters 6–9. These diesters (6–9) on stirring with bis(3-aminopropyl)amine and diethylenetriamine in methanol–toluene (1:1) mixture undergo intermolecular cyclization to give respective thia-aza macrocycles 10–15. The alkylation of macrocycles 10–13 with 9-anthracenylmethyl chloride gave amine N-(anthracenylmethyl) substituted macrocycles 16–19. The extraction profile of macrocycles 10–15 towards alkali (Li⁺, Na⁺, K⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), Ag⁺, Tl⁺ and Pb²⁺ picrates shows preferential extraction of Ag⁺ with these macrocycles. The macrocycles 16–19 show fluorescence spectrum typical of anthracene moiety and depending on their structures exhibit 0–80 times increase in fluorescence on addition of transition metal ions. Fluorescent receptors 16, 17, and 19 are capable of functioning as a very efficient multi input OR logic gate.

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Graphical abstract 1,3- and 1,4-Bis(bromomethyl)benzene and its substituted derivatives undergo nucleophilic substitution with methyl mercaptoacetate to provide respective diesters 6–8. These diesters (6–8) on stirring with bis(3-aminopropyl)amine in methanol–toluene (1:1) mixture undergo intermolecular cyclization to give respective thia-aza macrocycles 10–12. The alkylation of macrocycles 10–12 with 9-anthracenylmethyl chloride gave amine N-(anthracenylmethyl) substituted macrocycles 16–18. The macrocycles 16–18 exhibit 0–80 times increase in fluorescence on addition of transition metal ions.

     

The nitro aromatic compounds detection by triazole carboxylic acid and its complex with the fluorescent property

The 5-methyl-1-(4-nitrophenyl)-1H-1, 2, 3-triazole-4-carboxylic acid (1) was synthesized by an improved method. By using the compound 1 as ligand, a new complex [Cu(L)₂][Cu(L)₂(H₂O)₂] (2) was prepared firstly under hydrothermal condition. Both 1 and 2 were all used as exclusive fluorescence sensor for 2, 4, 6-trinitrophenol (TNP) for the first time. The fluorescence exploration demonstrated that they exhibit highly selective and sensitive (K_SV = 393685 M^?1 and K_SV = 213269 M^?1, respectively) sensing to TNP from other nitro aromatic compounds (NACs) with high quenching efficiency QP value of 96.76% and 93.37%, as well as low detection limit (0.68 μM and 0.37 μM, respectively). It means that complex 2 had higher selectivity due to the less interference by 4-NT and 2-NP compared with 1. Moreover, the fluorescence quenching phenomenon of sensor 1 with TNP was analyzed by density functional theory (DFT).     

Coumarin-based dual fluorescent spin-probes

New, dual profluorescent spin-probes and their fluorescent amine analogues, as potential spin traps, have been synthesized and characterized. Comparison between the fluorescence spectra of amines and their corresponding nitroxides established spacer distance dependent quenching of fluorescence.     

Amide–Amide Hydrogen Bonding. Semirubin Amides

Summary. Semirubins are analogs for one-half of the bilirubin structure and capable of intramolecular hydrogen bonding. Semirubin amides of ammonia and primary amines are also capable of intramolecular hydrogen bonding. From a combination of spectroscopic methods (¹H NMR, NOE, and VPO), the primary amide is found to engage very effectively in intramolecular hydrogen bonding. The secondary and tertiary amides engage in both intramolecular (i) and intermolecular (ii) hydrogen bonding: N-methyl (i, monomer + ii, dimer), N-tert-butyl (ii, dimer), N,N-diethyl (i, monomer + ii, dimer). With an oxo-group at C(10), all of the amides are monomeric and most engage in intramolecular hydrogen bonding.