Magnetic field induced cross relaxation between two different spin transitions of triplet coumarin

At certain magnetic fields, when the energy separations between the τ_x — τ_y spin levels and between the τ_y — τ_z levels of triplet coumarin become equal, intensity changes are observed in the phosphorescence of coumarin doped in a single crystal of durence cooled to 1.6 K that can be attributed to cross relaxation (CR) between the τ_x — τ_y spin levels of one triplet coumarin molecule and the τ_y — τ_z spin levels of another triplet coumarin. Rate equations that describe the time behavior of the populations of the spin levels which are involved in the CR process are described and numerically solved. CR behavior is found to be strongly dependent on the total coumarin triplet concentration.     

Synthesis,spectroscopy, electrochemistry and in situ spectroelectrochemistry of partly halogenated coumarin phthalonitrile and corresponding metal-free,cobalt and zinc phthalocyanines

In this study, the preparation of novel 7-hydroxy-3-(2-chloro-4-fluorophenyl)coumarin (1), the ligand, 7-(3,4-dicyanophenoxy)-3-(2-chloro-4-fluorophenyl)coumarin (2), metal-free phthalocyanine 3 and metallophthalocyanine complexes 4 and 5 (MPcs, M = Co, Zn), β-substituted with 7-oxo-3-(2-chloro-4-fluorophenyl)coumarin functional group was achieved. By the reaction of 7-hydroxy-3-(2-chloro-4-fluorophenyl)coumarin (1) with 1,2-dicyano-4-nitrobenzen in dry DMF as the solvent in the presence of K₂CO₃ as the base, the 7-(3,4-dicyanophenoxy)-3-(2-chloro-4-fluorophenyl)coumarin (2) was synthesized. Compound 2 reacted with Co(CH₃COO)₂·4H₂O in 2-N,N-dimethylaminoethanol to furnish a novel coumarin containing cobalt(II) phthalocyanine 4. The cyclotetramerization of 2 with Zn(CH₃COO)₂·2H₂O in 2-N,N-dimethylaminoethanol gave the novel coumarin containing Zn(II)phthalocyanine 5; while tetramerization without any metal salts in 2-N,N-dimethylaminoethanol gave the metal-free phthalocyanine 3. The structures of obtained compounds were confirmed by elemental analysis, UV–Vis, IR, MALDI-TOF mass and ¹H NMR spectra. The cyclic and differential pulse voltammetry, and in situ spectroelectrochemistry of 7-oxo-3-(2-chloro-4-fuorophenyl)coumarin substituted phthalocyanines 3, 4 and 5 allowed us to identify metal- and phthalocyanine ring-based redox processes of the complexes.     

Host-Guest Interactions and Laser Activity in AlPO4-5/Laser Dye Composites

In situ inclusion of the laser dyes coumarin 466, coumarin 7, pyridine 2 and DCM has been conducted successfully in AlPO₄-5 crystals. The charged molecule pyridine 2 interacts with the framework and leads to bundle-like morphologies with increasing dye content. Uncharged molecules (DCM, coumarin 7, coumarin 466) are included, although corresponding molecular dimensions are exceeding pore size. These dyes probably induce local defects in the pore walls of AlPO₄-5 which are healed during crystal growth leading to well-developed hexagonal prisms. Spectroscopic studies show interactions of the dyes with the solid-state matrix which are reflected by shifts of absorption and emission maxima of the dyes. For the first time, laser activity is demonstrated on a perfect hexagonal single AlPO₄-5/DCM crystal.     

Coumarins with an unprecedented tetracyclic skeleton and coumarin dimers from chemically engineered extracts of a marine-derived fungus

The unprecedented tetracyclic coumarin derivatives 1 and 2 and the coumarin dimers 3–5 were isolated from chemically engineered extracts (coumarin dimerization of natural extract) of the marine-derived fungus Eurotium rubrum. The structures of these compounds were established using NMR, MS and IR methods. The absolute configuration of 1 was determined by ECD calculations. The unprecedented tetracyclic coumarin skeleton was generated by domino-Knoevenagel-Diels-Alder reactions. Compounds 1–5 showed tyrosinase inhibitory activity (IC₅₀?=?1.7, 1.2, 4.9, 1.8 and 2.9?μM, respectively). The isolated coumarin derivatives 1–5 were not observed by HPLC analysis in crude extracts of E. rubrum, suggesting that chemically engineered extract generated these new coumarin derivatives with tyrosinase inhibitory activity.     

4-Chloro-3-(trifluoroacetyl)coumarin as a novel building block for the synthesis of 7-(trifluoromethyl)-6H-chromeno[4,3-b]quinolin-6-ones

4-Chloro-3-(trifluoroacetyl)coumarin was synthesized for the first time via direct TMSCl-mediated acylation of 4-hydroxycoumarin with TFAA followed by the treatment with POCl₃. The reaction of 4-chloro-3-(trifluoroacetyl)coumarin with commercially available anilines is a two-step method, which affords a set of 7-(trifluoromethyl)-6H-chromeno[4,3-b]quinolin-6-ones in good to excellent yields.     

In Vitro Inhibition Effect of Some Dihydroxy Coumarin Compounds on Purified Human Serum Paraoxonase 1 (PON1)

Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro inhibition effect of some dihydroxy coumarin compounds namely 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (A), 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (B) and 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (C) on purified PON1 were investigated by using paraoxon as a substrate. PON1 was purified using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-l-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The purified enzyme had a specific activity of 11.76?U/mg. The dihydroxy coumarin derivatives of A and B compounds inhibited PON1 enzyme activity in a noncompetitive inhibition manner with K _i of 0.0080?±?0.256 and 0.0003?±?0.018?mM values, respectively. C compound exerted an uncompetitive inhibition of PON1 enzyme activity with K _i of 0.0010?±?0.173?mM. Moreover, dihydroxy coumarin derivatives of A, B and C compounds were effective inhibitors on purified human serum PON1 activity with IC₅₀ of 0.012, 0.022 and 0.003?mM values, respectively. IC₅₀ value of unsubstituted 6,7 dihydroxy coumarin was found as 0.178?mM. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.     

Asymmetric conjugate additions to 1,1′-diactivated cyclic enones—a comparative study

A study of copper-phosphoramidite-catalysed ZnR₂ and AlR₃ additions to 1,1′-dicarbonyl-activated cyclic Michael acceptors has revealed high enantioselectivities for AlR₃ (R = Me, Et) 1,4-addition to a range of 3-acylcoumarins (85–98% ee, trans:cis ～90:10) using commercial or readily available ligands. Large substituents at the 6-position, and to some extent at the 5-position, of the coumarin are less well tolerated, nor is truncation of the coumarin motif to a comparable 2-acylcyclohexenone (ee values up to 78%).     

A consecutive one-pot two-step approach to novel trifluoromethyl-substituted bis(indolyl)methane derivatives promoted by Sc(OTf)3 and p-TSA

A one-pot two-step reaction of 3-(trifluoroacetyl)coumarin and indole afforded trifluoromethyl-substituted bis(indolyl)methane compounds containing coumarin skeleton. The atomic economic and simply manipulative reaction involved premier treatment of reaction mixtures with Sc(OTf)₃, followed by p-TSA in one-pot process. The reaction proceeded to give the title compounds in high yields (up to 95% yield).     

Synthesis,characterization and fluorescence behavior of new fluorescent probe phthalocyanines bearing coumarin substituents

In this study, we report a new ligand, 6-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)phenyl]coumarin, and its fluorescent tetrasubstituted phthalocyanines {M[Pc(OBzCou)₄], M = 2H, Zn(II), Co(II); Bz: Benzene}. The effect of the coumarin derivative on the intensity of the fluorescence spectra of the metal-free (H₂Pc) and zinc phthalocyanine (ZnPc) derivatives was investigated. The change of the emission properties of both the coumarin moieties and the phthalocyanine core in the presence of the metal ion and the ring-opening reaction of the coumarin were studied by means of steady-state fluorescence spectroscopy. The radiative decay of the Pcs and the treated coumarin substituents bound to the Pcs was examined. The novel chromogenic compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Maldi-TOF, IR and UV–Vis spectral data. The photophysical properties of the Pcs are extensively affected by their state of aggregation: in particular, dimerization and aggregation result in a remarkable modification of the absorption and emission bands and may induce significant quenching of the usually strong Pc fluorescence. The electronic spectra exhibit a band of coumarin identity together with characteristic Q and B bands of the phthalocyanine core.     

Synthesis of poly(vinyl acetate) with fluorescence via a combination of RAFT/MADIX and “click” chemistry

A novel ω-azido-functionalized RAFT reagent, O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC), was synthesized and subsequently employed to mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc) to prepare end-functionalized polymers. The polymerization results showed that the RAFT polymerizations of VAc could be well controlled using AEBDC as the RAFT agent. Number-average molecular weights (M_n GPC) increased linearly with monomer conversion, and molecular weight distributions were relatively narrow. ¹H NMR spectrum of the poly(vinyl acetate) (PVAc) confirmed the existence of functional azido group at the end of the polymers chains. The ω-azido-terminated polymers were coupled by “click” chemistry with a fluorescent alkyne, 7-propinyloxy coumarin, to prepare fluorescent PVAc. The fluorescence properties of the PVAc homopolymers before and after coupling with 7-propinyloxy coumarin in CH₂Cl₂ solution were investigated.     

Performance of dye-sensitized solar cells based on various sensitizers applied on TiO2-Nb2O5 core/shell photoanode structure

The present investigation described the performance of dye-sensitized solar cells (DSSCs) based on various sensitizers applied on TiO₂-Nb₂O₅ core/shell photoanode film. The novel photoanodes were prepared using composite of TiO₂ nanoparticles (TNPs) and TiO₂ nanorods (TNRs) as core (TNPRs) layer with Nb₂O₅ shell coating. As well, tantalum pentoxide (Ta₂O₅), a blocking layer applied over the core/shell film. The DSSCs were fabricated based on various sensitizers namely zinc phthalocyanine, indoline, indigo carmine, zinc porphyrin, N719, coumarin NKX-2700, polymer dye, quantum dots (QDs), perylene and squaraine. The I–V characteristics of the DSSCs, photocurrent density (Jsc), open-circuit voltage (Voc), fill factor (FF), and photoconversion efficiency (PCE) were determined under illumination of AM 1.5 G. Electrochemical impedance spectroscopy (EIS) analysis is carried out to study the charge transport and life-time of charge carriers at photoanode/dye/electrolyte interface of the DSSCs. The I–V and EIS results explicated that the core/shell with blocking layers were able to alleviate the electron transport and suppressed charge recombination at photoanode/dye/electrolyte interface of the DSSCs. Concerning the sensitizers, PCE of the DSSCs exemplify the order N719 > zinc porphyrin > coumarin NKX-2700 > indoline > squaraine > QDs > zinc phthalocyanine > perylene > polymer dye > indigo carmine dye. The results of the present work demonstrated that among the sensitizers studied, N719 showed the highest PCE and fill factor. Besides, the metal-free organic sensitizers (coumarin NKX-2700 and indoline) exhibited comparable PCE as compared to N719.     

Design,Synthesis and Bioactivity Evaluation of Coumarin–BMT Hybrids as New Acetylcholinesterase Inhibitors

Coumarin possesses the aromatic group and showed plentiful activities, such as antioxidant, preventing asthma and antisepsis. In addition, coumarin derivatives usually possess good solubility, low cytotoxicity and excellent cell permeability. In our study, we synthesized the compound bridge methylene tacrine (BMT), which has the classical pharmacophore structure of Tacrine (THA). Based on the principle of active substructure splicing, BMT was used as a lead compound and synthesized coumarin–BMT hybrids by introducing coumarin to BMT. In this work, 21 novel hybrids of BMT and coumarin were synthesized and evaluated for their inhibitory activity on AChE. All obtained compounds present preferable inhibition. Compound 8b was the most active compound, with the value of K_i as 49.2 nM, which was higher than Galantamine (GAL) and lower than THA. The result of molecular docking showed that the highest binding free energy was −40.43 kcal/mol for compound 8b, which was an identical trend with the calculated K_i.     

Synthesis,crystal structure and photoluminescence of 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin

A new coumarin derivative, 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin, was synthesized and characterized by FT-IR, ¹H NMR, element analysis and single crystal X-ray crystallography. The dihedral angle of benzo[5,6]coumarin ring and phenyl group is 36.15°, and the dihedral angle of phenyl group and anthracene skeleton is 89.37°. The UV–vis absorption and photoluminescence of the compound were discussed. The result shown that the compound exhibits high fluorescence quantum yield (Φ_F), large Stokes shift and green emission (508 nm). The molecular structure of the compound was optimized using density functional theory (DFT) at B3LYP/6-31G(d) level, and the HOMO and LUMO levels of the compound were deduced.     

A novel optically active bisphosphine ligand CDP,derived from an anti head-to-head coumarin dimer: synthesis and application to the rhodium-catalyzed asymmetric hydrogenation of arylenamides

A novel optically active bisphosphine ligand CDP containing a C₂-symmetric cyclobutane ring was prepared from an enantiopure anti head-to-head coumarin dimer. CDP was successfully applied to the rhodium-catalyzed asymmetric hydrogenation of arylenamides, affording the corresponding amides up to 93% e.e.     

Photocleavage of dimers of coumarin and 6-alkylcoumarins

The cleavage of four coumarin dimers, the syn-head-to-tail (ht) dimer of parent coumarin (syn-ht-CC1), the anti- and syn-hh dimers of 6-methylcoumarin (anti-hh-CC2 and syn-hh-CC2, respectively) and the anti-hh dimer of 6-dodecylcoumarin (anti-hh-CC3), was studied by UV–vis and IR spectroscopy and HPLC upon direct 254 nm irradiation as well as sensitized excitation. The quantum yield of dimer splitting is Φ_sp = 0.1–0.3 in various solvents and the effects of structure and solvent polarity are small. In certain solvents some of the dimers produced CO₂ along with the monomers in the splitting reaction. Electron transfer from dimers to the triplet state of sensitizers, such as benzophenone or 9,10-anthraquinone, was observed in acetonitrile.     

Interaction of Coumarin 7 and Coumarin 314 with C-hexylpyrogallol[4]arene

We report in this paper the different modes of interaction of coumarin 7 and coumarin 314 with the cavity-containing molecule C-hexylpyrogallol[4]arene. The stoichiometry and the binding constant of coumarin 7 for its binding with C-hexylpyrogallol[4]arene are reported. The analysis is done with UV–Vis absorption, steady-state and time-resolved fluorescence, and 2D ROESY spectroscopy. The fluorescence quenching of the two coumarins is analyzed and the Stern–Volmer constants are reported. The mode of binding of coumarin 7 with the host molecule is optimized with 2D ROESY. Coumarin 314 does not form an inclusion complex and this result is supported by the spectral data. The ground and the excited state pK _a values for the coumarins, in the presence of C-hexylpyrogallol[4]arene, are reported.     

Synthesis and photoluminescent properties of 7-N,N-diphenylamino-3- benzoheterocyclic coumarin derivatives

Two new 7-N,N-diphenylamino-3-benzoheterocyclic coumarin derivatives containing electron-transporting benzotriazolyl or benzoxazolyl moiety, 3-(1-benzotriazole)-7-N,N-diphenylaminocoumarin (BTDC) and 3-(2-benzoxazole)-7-N,N-diphenylaminocoumarin (BODC), were synthesized and characterized by element analysis, ¹H NMR and FT-IR spectra. The UV–vis and fluorescence spectra of these coumarin derivatives were investigated. The results show that BTDC and BODC exhibit strong blue and red emissions, respectively, under ultraviolet light excitation. The relationships between the chemical structure and the fluorescence characteristics of the 7-N,N-diphenylamino-3-benzoheterocyclic coumarin derivatives are discussed. It was found that the coumarin derivative will become a high-efficiency emitting material when an amino group is attached in 7-position of the coumarin ring, and 7- strong electron donors can improve the ability of the intramolecular charge transfer of the coumarin molecules.     

Microbial reduction of coumarin, psoralen, and xanthyletin by Glomerella cingulata

Microbial transformation of coumarin, psoralen, and xanthyletin was performed with the fungus Glomerella cingulata. The main reaction pathways involved reduction at α,β-unsaturated δ-lactone ring on coumarin analogue. Coumarin was metabolized by G. cingulata to give the corresponding reduced acid, hydrocoumaric acid. In the biotransformation of psoralen, two reduced metabolites, 6,7-furano-hydrocoumaric acid, and 6,7-furano-o-hydrocoumaryl alcohol were isolated from the incubation of psoralen. Xanthyletin was converted to reduced products 9,9-dimethyl-6,7-pyrano-hydrocoumaric acid and 9,9-dimethyl-6,7-pyrano-o-hydrocoumaryl alcohol by G. cingulata. The structures of the new compounds were characterized using spectroscopic techniques. In addition, all of compounds including methyl ester derivatives of the metabolites were tested for the β-secretase (BACE1) inhibitory activity in vitro. 6,7-Furano-hydrocoumaric acid methyl ester was shown to possess BACE1 inhibitory activity, and an IC₅₀ value was 0.84 ± 0.06 mM.     

5-Demethoxy-10′-ethoxyexotimarin F,a New Coumarin with MAO-B Inhibitory Potential from Murraya exotica L.

Rutaceae plants are known for being a rich source of coumarins. Preliminary molecular docking showed that there was no significant difference for coumarins in Clausena and Murraya, both of which had high scoring values and showed good potential inhibitory activity to the MAO-B enzyme. Overall, 32 coumarins were isolated from Murraya exotica L., including a new coumarin 5-demethoxy-10′-ethoxyexotimarin F (1). Their structures were elucidated on the basis of a comprehensive analysis of 1D and 2D NMR and HRMS spectroscopic data, and the absolute configurations were assigned via a comparison of the specific rotations and the ECD exciton coupling method. The potential of new coumarin (1) as a selective inhibitor of MAO-B was initially evaluated through molecular docking and pharmacophore studies. Compound (1) showed selectivity for the MAO-B isoenzyme and inhibitory activity in the sub-micromolar range with an IC₅₀ value of 153.25 ± 1.58 nM (MAO-B selectivity index > 172).     

Convenient synthesis of fused pyrano[3,2-h]- and furo[3,2-h]benzo[f]coumarins from naphthalene-2,3-diol

The treatment of 8-propargyloxy-benzo[f]coumarin with boron trifluoride diethyl etherate in N,N-dimethylformamide under reflux or MW irradiation resulted in pyrano[3,2-h]benzo[f]coumarin, while the furo[3,2-h]benzo[f]coumarin is received from the treatment with N-methylformamide under MW irradiation.