Synthesis and fluorescence properties of side-chain carboxylated 5,9-diaminobenzo[a]phenoxazinium salts

The efficient synthesis of a series of novel side-chain carboxylated 5,9-diaminobenzo[a]phenoxazinium salts is described. The ring system was prepared by the reaction of 5-alkylamino-2-nitrosophenol hydrochlorides with the appropriate N-alkylated-naphthylamine. Evaluation of the visible and fluorescence properties of the cationic dyes was carried out in ethanol and water at physiological pH. In both solvents they showed intense visible absorption maxima in the range 500-638 nm (ethanol) and 625-650 (water), and fluoresced strongly, with fluorescence maxima from 612 to 669 nm (ethanol) and from 654 to 685 nm (water). A wide variation in fluorescence quantum yields is observed, ranging from 0.051 to 0.50 and 0.065 to 0.32 in ethanol and water, respectively.     

New confined p-phenylenevinylene (PPV)-type polymer analogue of poly(phenylene sulfide)

A new confined p-phenylenevinylene (PPV)-type polymer (PPVS) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by ¹H NMR, ¹³C NMR, and FTIR spectroscopic analysis. PPVS contains oligomeric PPV units separated by sulfide bridges in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 3500 g mol⁻¹. Thermogravimetric analysis and differential scanning calorimetry indicate that PPVS is amorphous, stable up to 360 °C in air and displays a glass transition temperature of 98 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. The polymer film absorbs at 375 nm and emits at 517 nm with a narrow emission spectrum. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 2.78 eV. A single-layer diode device of the configuration indium-tin oxide/PPVS/aluminium has been fabricated and has a relatively low turn-on voltage of 3.4 V. An electroluminescent emission similar to photoluminescence is demonstrated in a multilayer device.     

Synthesis,self-assembly and optical properties of novel fluorescent alkoxy-substituted fluoroaryl 1, 3, 4-oxadiazole organogelator

Aromatic nucleophilic substitution (S_NAr) reactions have been known to be regioselective to the para position on a variety of substituted perfluorobenzenes. In the current study, a series of fluoroaryl 1, 3, 4-oxadiazole derivatives substituted with different para terminal ethers were synthesized using S_NAr chemistry to afford fluorescent and thermally reversible low molecular weight organogelators (LMWOs). S_NAr was used to synthesize these highly fluorinated organogelators in high purity and good yields starting from pentafluorobenzoic acid and 4′-hydroxy-4-biphenylcarbonitrile. These fluorinated 1, 3, 4-oxadiazole derivatives were characterized by elemental analysis, FTIR, and ¹H, ¹³C, and ¹⁹F NMR spectroscopy. The photophysical properties of those organogelators were described. Both UV–visible absorption and fluorescence spectral profiles displayed a solvatochromic and solvatofluorochromic properties. The absorption maxima for the developed organogelators were monitored in the range of 260–289 nm, whereas the emission maxima were monitored in the range of 278–305 nm. The best gelation properties were monitored for the hexyloxy-substituted 2-(biphenylyl)-5-(perflurophenyl)-1, 3, 4-oxadiazole gelator in different solvents with critical gel concentrations in the range of 1.86–5.07 mM. The self-assembly process was monitored to occur via van der Waals forces and π-π stacks to result in gelation of solvents. Scanning electron microscope (SEM) demonstrated nanofiber-like structures (350–550 nm). The thermal stability of the hexyloxy-substituted organogel was monitored at 48 °C. Both cytotoxicity and antimicrobial activity of the produced fluoroaryl 1, 3, 4-oxadiazole derivatives were explored to verify their potential use for biomedical applications, such as drug delivery and bioimaging.     

Synthesis of short and long-wavelength functionalised probes: amino acids' labelling and photophysical studies

Fluorescent labelling of α-amino acids at their N or C terminals in the main and lateral chains at short and long wavelengths was carried out in different ways. The N-[3-(naphthalen-1-ylamino)propanoyl]amino acid methyl esters synthesised showed strong fluorescence in the visible region (∼415 nm) of the electromagnetic spectrum. Condensation of these compounds with 5-diethylamino-2-nitrosophenol or 5-ethylamino-4-methyl-2-nitrosophenol produced the benzo[a]phenoxazine derivatives, with maximum emission wavelengths shifted to values higher than 644 nm. The synthesis of novel functionalised 5,9-diaminobenzo[a]phenoxazinium salts, by reaction of 5-ethylamino-4-methyl-2-nitrosophenol and N-substituted 1-naphthylamine and their use in the covalent labelling of the N or C terminals of valine, produced derivatives with long-wavelength emissions (644-653 nm). Photophysical studies using the synthesised compounds both in different solvents and in controlled pH were undertaken. Preliminary evaluation of photostability of the cationic polycyclic heterocycles in ethanol and water at physiological pH was also performed.     

One-pot synthesis of β-carboxy tetra aryl porphyrins: potential applications to dye-sensitized solar cells

A facile one-pot conversion of 2-formyl-5,10,15,20-tetra aryl-substituted porphyrins and their zinc derivatives to the corresponding 2-carboxy-5,10,15,20-tetra aryl-substituted porphyrins was achieved for the first time by using hydroxylamine hydrochloride and phthalic anhydride. All these substituted carboxy porphyrins were completely characterized by using mass, CHN analysis, ¹H NMR, UV-vis, Fluorescence spectroscopies, and cyclic voltammetry. Both the absorption maxima and emission maxima were red shifted by 5-7 nm. The LUMO of these porphyrins are above the TiO₂ conduction band and HOMO was below the redox electrolytes. These carboxy porphyrins are potential applications as sensitizers to dye-sensitized solar cell.     

Synthesis, electrochemical and photophysical properties of β-carboxy triaryl corroles

An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III) derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting mild reaction conditions by using hydroxylamine hydrochloride and phthalic anhydride. All these substituted carboxy corroles were completely characterized by using Mass, CHN analysis, IR, ¹H NMR, UV-vis., Fluorescence spectroscopies, and cyclic voltammetry. Both the absorption maxima and emission maxima of carboxy corroles were red shifted by 5-13 nm. The LUMO level of these corroles is above the TiO₂ conduction band and HOMO level was below the redox electrolytes. These β-carboxy corroles confined with may find applications as sensitizers in dye-sensitized solar cells.     

First observation of intra-5f fluorescence from an actinyl center: Np(VI) near-IR emission in Cs2U(Np)O2Cl4

Fluorescence from an excited 5f state of Np(VI) has been observed in the doped impurity system Cs₂U(Np)O₂Cl₄. This is the first intra-5f fluorescence transition that has been detected at room temperature in a condensed-phase system with an actinyl (An(VI)O₂²⁺) core, and it is a rare example of fluorescence of any kind from non-uranyl ions of this type. The emission originates from an excited state approximately 6890 cm⁻¹ above the ground state. Its emission spectrum and fluorescence lifetime at 295 K will be discussed. Vibronic structure in the emission spectrum is assigned based on comparison with the detailed analysis of the absorption spectra published by Denning et al.     

Synthesis, characterization and fluorescence study of new polyacrylates containing stilbene

A new urethane acrylic monomer with stilbene in its structure, trans-4-(2-methacryloyloxyethylcarbamoyloxymethyl)stilbene (SUM), was synthesized to be further free radically copolymerized with methyl methacrylate (MMA). The structures of SUM and the resulting copolymer, trans-4-(2-methacryloyloxyethylcarbamoyloxymethyl)stilbene-co-methyl methacrylate (SUMMA) were characterized by ¹H NMR, UV-vis and FTIR spectroscopy, differential scanning calorimetry (DSC), TGA and fluorescence spectroscopy. From the ¹H NMR spectrum of the formed copolymer, a composition of about 1:2.6 (SUM/MMA) was determined. The photochemical behavior of the stilbene moieties in polymer was investigated in solution (DMF) and in film state comparatively to that of SUM, following the decreasing under UV irradiation of the π-π∗ absorption band characteristic to the trans-isomer in the UV spectra. Morphologic changes in the surface of the polymeric film during the photoisomerization were visualized by means of atomic force microscopy (AFM) and it is proposed that the new formed cone-shaped structures from the irradiated surface to be attributed to J-aggregates. Analysis of fluorescence shows that the stilbene derivatives showed both monomer emission at 358 (SUM) and 357 nm (SUMMA), and excimer (aggregate) emission at 391 and 412 nm (SUM), and at 374 and 398 nm (SUMMA) in solution. Quenching of the active species (SUMMA) by aliphatic amines shows that this process involves an electron transfer from the ground-state amine to excited stilbene, more efficiently being triethylamine.     

Synthesis and photophysical behaviors of temperature/pH-sensitive polymeric materials. I. Vinyl monomer bearing 9-aminoacridine and polymers

A novel acrylic monomer bearing acridinyl group, acridine-9-N-acrylamide (Ac-9AA) was synthesized from 9-aminoacridine (9AA) and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CCl₂) at room temperature. The synthesized Ac-9AA was identified by IR, MS and ¹H NMR spectra. Homopolymer of Ac-9AA was obtained using AIBN as a thermal initiator in THF under 65-70 °C and the average molecular weights (M_w) of poly(Ac-9AA) obtained was very low, being in the order of ca. 10³. Copolymer of Ac-9AA and acrylamide was synthesized with thermal initiator and poly(Ac-9AA-co-AM) was characterized by the method of IR, UV-vis and DSC. The photophysical behaviors of Ac-9AA and its polymers were explored by recording the fluorescence spectra in solution, solid and film. In addition, the pH and temperature dependence on fluorescence of the water-soluble poly(Ac-9AA-co-AM) were investigated in detail. The results showed that the relative fluorescence intensity of poly(Ac-9AA-co-AM) had an excellent linear response to temperature in the range of 0-60 °C. Moreover, the fluorescence intensity increased continuously from low pH to high pH while the excitation maxima at 388 nm and emission maxima at 400 nm had redshift after the addition of HCl or NaOH, which results from the fact that the predominance of tautomeric forms of Ac-9AA changed at different medium. This investigation may provide a convenient way to prepared multifunctional macromolecule biomaterial bearing aminoacridine to probe pH and temperature in biological system.     

New approach to preparation of N-acylphosphoramido(thio)(seleno)ates

N-[2-(X)-1,3,2-Oxathiaphospholane] derivatives (X = S, Se, O) of carboxamides were prepared and their DBU-assisted reaction with alcohols led to the corresponding O-alkyl-N-acylphosphoramido(thio)(seleno)ates. Their structures were confirmed by MS analysis and ¹H and ³¹P NMR spectroscopy. Independently N-acylphosphoramidoselenoates were converted to N-acylphosphoramidates by treatment with tert-butylperoxytrimethylsilane. The oxathiaphospholane approach was also applied to the synthesis of derivatives having N-prolylphosphoramido(thio)(seleno)ate linkages on the 5′-OH group of AMP.     

Microwave-assisted clean synthesis of aromatic photoactive polyamides derived from 5-(3-acetoxynaphthoylamino)-isophthalic acid and aromatic diamines in ionic liquid

Dicarboxylic acid, 5-(3-acetoxynaphthoylamino)isophthalic acid was prepared in three steps. The direct polycondensation of this novel diacid with several aromatic diamines was studied in 1,3-diisopropylimidazolium bromide as an ionic liquid (IL) under microwave irradiation and conventional heating. The polymerization reaction was effectively preceded in IL, and triphenyl phosphite as an activating agent, and the resulting novel photoactive polyamides were obtained in high yields and moderate inherent viscosities in the range of 0.44-0.69 dL/g. Thermogravimetric analysis showed that polymers are thermally stable, 10% weight loss temperatures in excess of 390 and 470 °C, and char yields at 600 °C in nitrogen higher than 60%. These macromolecules exhibited maximum UV-vis absorption at 265 and 300 nm in N,N-dimethylformamide (DMF) solution. Their photoluminescence in DMF solution demonstrated fluorescence emission maxima around 361 and 427 nm for all of the polyamides. It is very important to note that, because of, high polarizability of ILs, they are very good solvents for absorbing microwaves.     

Novel photoluminescent lanthanidomesogens forming bilayer smectic phase derived from blue light emitting liquid crystalline, one ring O-donor Schiff-base ligands

A series of new mononuclear lanthanide(III)-salicylaldimine complexes of the type [Ln(LH)₃(NO₃)₃] (Ln = La, Pr, Sm and Gd; LH = N-(2-hydroxyethyl)-4n-alkoxysalicylaldimine, n = 14, 18) have been synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, UV-Vis, FAB-mass and magnetic susceptibility measurements. The ligand (LH) coordinate to lanthanide ions in zwitterionic form via the phenolic-oxygen with the proton shifted to the imine-nitrogen. The nitrato groups occurring in chelated bidentate fashion complete a nine-coordinate geometry. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) show that the ligands are monotropic and their complexes exhibit enantiotropic highly viscous smectic A (SmA) mesophase in the temperature range 60-185 °C. A bilayer self organized assembly of the molecules in the mesophase are proposed on the basis of the small angle XRD study. The ligands are blue light emitters with a broad emission maxima at ∼447 nm while the lanthanide complexes show intense emission in the visible range (∼465-679 nm) at 350 nm excitation. The samarium(III) complex, [Sm(LH)₃(NO₃)₃] is distinct from the rest in emitting bright orange light (∼660 nm, Φ = 48%). The S_o-S₁ excitation band being stronger than the direct f-f excitation in the samarium complex clearly suggests that the Schiff-base ligands efficiently sensitize the luminescence of Sm³⁺. DFT calculations have been performed using DMol3 program at BLYP/DNP level to obtain the stable electronic structure of the ligand and complex.     

Synthesis and binding properties of carboxylphenyl-modified calix[4]arenes and cytochrome c

Two novel carboxylphenyl-modified calix[4]arenes, tetrakis-carboxylphenylcalix[4]arene (TCPC) and 1,3-bis-carboxylphenylcalix[4]arene (BCPC), as well as a corresponding analogue for comparison, tetrakis-phenylcalix[4]arene (TPC), have been synthesized by palladium-catalyzed Suzuki cross-coupling of arylboronic acid and tetrabromocalix[4]arene as a key step. The binding properties of these calix[4]arene derivatives with bovine heart cytochrome c (cyt c) in dimethylformamide (DMF) was investigated by fluorescence spectroscopy. The binding affinity in the order of TCPC > BCPC ? TPC reflects a clear dependence on the number of carboxyl ligating groups attached onto a receptor and suggests the electrostatic force may be the predominant factor driving the complexing process. The stable 1:1 complexes of TCPC and BCPC with cyt c were evidenced with the binding constants of 3.15 × 10⁶ and 5.85 × 10⁵ L mol⁻¹, respectively. Due to a large overlap between the emission spectrum of TCPC and the absorption spectrum of cyt c, and a short interaction distance (estimated to be 5.6 nm) between them, the fluorescence quenching of TCPC upon complexation with cyt c is attributed to an efficient energy transfer.     

The Re(I) coordination chemistry of a series of pyrido[2,3-b]pyrazine-derived ligands: Syntheses,characterisation and crystal structures

Reaction of 2,3-diaminopyridine with one equivalent of a functionalised vicinal diketone, in ethanol, yields a series of ligands based upon the pyrido[2,3-b]pyrazine core. The ligands were characterised by ¹H, ¹³C–{¹H} NMR, MS and UV–Vis spectroscopy. Reaction of the ligands with one equivalent of {ReBr(CO)₅} gave a series of Re-Lⁿ complexes based upon the general formula fac-{ReBr(CO)₃(L)} (where L = pyrido[2,3-b]pyrazine-derived ligands, L¹–L⁶). Solution IR studies confirmed the retention of the facially capped, tri-carbonyl coordination geometry at rhenium, and ¹H NMR studies confirmed coordination of the ligand to Re(I). EI HR MS data were obtained for each complex confirming the proposed formulation and stoichiometry. Single crystal X-ray structures were obtained for three of the complexes (Re-L¹, Re-L², Re-L⁶), with each demonstrating that the ligands coordinate to Re(I) in a bidentate manner, via a four-membered chelate ring, which was unsymmetrical in the former two cases. The electronic absorption spectra of the complexes showed absorption into the visible region ca. 375–500 nm, (the complexes are orange-red in appearance). Following irradiation at 350–450 nm, the complexes display a solid-state broad emission peaking between 600–700 nm. The complexes were not sufficiently luminescent in solution to allow further investigation into the origin of this emission band, although with reference to related 1,8-naphthyridine complexes of Re(I) it is likely to incorporate significant ³MLCT character.     

New and efficient high Stokes shift fluorescent compounds: unsymmetrically substituted 1,2-bis-(5-phenyloxazol-2-yl)benzenes via microwave-assisted nucleophilic substitution of fluorine

Two new unsymmetric derivatives of 1,2-bis-(5-phenyloxazol-2-yl)benzene (ortho-POPOP) were synthesized via microwave-assisted nucleophilic substitution of fluorine which appears to be significantly more efficient compared with conventional thermal activation. The compounds synthesized are characterized by high fluorescence Stokes shifts (6000-11,000 cm⁻¹) in solvents of various polarity, intermediate-to-high fluorescence quantum yields and lifetimes in the range of several nanoseconds.     

New star-shaped molecules derived from thieno[3,2-b]thiophene unit and triphenylamine

A series of new substituted triphenylamine (TPA) derivatives with alkyl thieno[3,2-b]thiophene and thiophene units were synthesized in a combinatorial manner. Suzuki coupling of a dioxaborolane TPA derivative and 2-bromo-3-nonylthieno[3,2-b]thiophene or Stille coupling of fresh stannyl thieno[3,2-b]thiophene was used. All compounds were characterized by ¹H and ¹³C NMR, HRMS, UV-vis spectrometry and DSC measurements. It was demonstrated that the optical and thermal properties of these materials can be tuned by varying both the conjugation length and thienothiophene and thiophene combination on the TPA branches. Moreover, the measured molar extinction coefficients were increasing from 63,000 (λ_max = 354 nm) to 131,000 L mol⁻¹ cm⁻¹ (λ_max = 428 nm) for TPA-thienothiophenes and TPA-bithiophene thienothiophenes, respectively. Some of them showed molecular glass behavior.     

Synthesis and characterization of some new mononuclear ruthenium complexes containing 4-(un)substituted dipyridylpyrazole ligands

A mononuclear ruthenium complex [Ru(bpy)₂(bpp)](PF₆) (1) and its halogenated and nitro derivatives [Ru(bpy)₂(Xbpp)](PF₆) (bpy = 2,2′-bipyridine; bpp = 3,5-bis(2-pyridyl)pyrazole; X = Cl, 2; X = Br, 3; X = I, 4; X = NO₂, 5) have been synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, elemental analysis. Complexes 2–5 have been further confirmed by X-ray diffraction. Their UV–Vis and emission spectroscopies, electrochemical measurements and acid–base properties are described. The results presented here reveal that the introduction of Cl, Br, I and NO₂ groups to the coordinated bpp⁻ ligand makes the absorption and emission maxima of the parent complex 1 blue-shifted, the oxidation potential of the Ru^II/Ru^III couple increased and the pK_a value decreased obviously. In addition, significant quenching of the emission by these groups is also observed.     

Development of non-symmetric thiophene-fused BODIPYs

A series of non-symmetric BODIPYs containing thieno[3,2-b]pyrrole moiety were synthesized in 21-63% yields. The absorption and emission maxima covered from the visible green to red region (λ_abs=532-647 nm; λ_em=547-664 nm; Φ_f=0.19-0.45). X-ray analysis indicated that the S-C bond lengths were shorter than those of thienopyrrole and thienohelicene by 0.03-0.05 Å. The crystal packing pattern suggested that strong π-π interaction, intermolecular C-H?F interaction, and weak S?π interaction existed. The tunable emission was achieved by structure modifications. Oxidation of BODIPY (λ_em=547 nm) with m-CPBA generated thiophene-1,1-dioxide derived BODIPY (λ_em=528 nm). Knoevenagel-type condensation of BODIPY with N,N-dimethylaminobenzaldehyde led to BODIPY (λ_em=693 nm) with extended conjugation.     

Development of a novel flow injection liquid-liquid microextraction method for the on-line separation and preconcentration for determination of zinc(II) using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a sensitive and selective fluorescent chemosensor

A novel flow injection analysis (FIA) system based on liquid-liquid microextraction and fluorimetric determination was developed for the determination of traces of the Zn²⁺ ion using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a sensitive and selective fluorimetric sensor, with λ_ex = 373 nm and λ_em = 530 nm, and hexanol as the extracting organic solvent. In the designed FIA system, the phase separation takes place via gravitation forces in the absence of any segmenter. The influence of pH and ionic strength of the solution, amount of ligand, nature of counter ion, volume of organic solvent, extraction time and coil length was investigated. Under optimized experimental conditions, the calibration curve found to be liner over a concentration range of 0.025-4.53 μg mL⁻¹ (R² = 0.9951) with a limit of detection of 2.3 ng mL⁻¹. The enrichment factor was 45 and relative standard deviation for 7 replicate determinations was 2.43%. The method is very fast and uses low levels of organic solvents. The proposed method was applied successfully to the determination of zinc(II) in human hair, human serum and two inorganic sludge samples.     

Synthesis and nonlinear optical properties of new symmetrically substituted stilbenes

Three new chromophores and trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(dimethyl amino) stilbene (DMANHAS) have been synthesized and whose chemical structures have been characterized by ¹H NMR, IR, and elemental analyses. Linear absorption, single-photon-induced fluorescence and two-photon-induced fluorescence are experimentally studied. Trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(dimethyl amino)stilbene (DMAHAS) and trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(diethyl amino)stilbene (DEAHAS) have effective two-photon absorption cross-sections of σ₂=0.91×10⁻⁴⁶ cm⁴ s/photon and σ₂=1.19×10⁻⁴⁶ cm⁴ s/photon at 532 nm by using an open aperture Z-scan technique, respectively. When pumped with 800 nm laser irradiation, DMAHAS and DEAHAS indicate strong two-photon-induced blue fluorescence of 436 and 440 nm, respectively, while trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(diethyl amino) stilbene (DEANHAS) and DMANHAS exhibit no fluorescence.