The synthesis and two-photon excited fluorescence properties of novel branched fluorene derivatives

Two novel, V-shaped fluorene derivatives branched from triphenylamine and their linear analogue were synthesized via Cu-mediated Ullmann condensation and subsequent Pd-catalyzed Heck coupling reaction. Their two-photon excited fluorescence properties as well as their linear absorption and single-photon excited fluorescence properties were examined. When excited at 730 nm by a Ti:sapphire femtosecond laser, the compounds exhibited strong two-photon excited blue fluorescence. The two-photon excited fluorescence cross-sections of V-shaped derivatives in toluene at 730 nm were 506 GM in the case of N, N-bis{7-[4′-(N, N-diphenylamino)styryl]-9,9-diethyl-9H-fluorene-2-yl}-aniline) and 397 GM for N, N-Bis{7-[4′-(N, N-diphenylamino)styryl]-9,9-diethyl-9H-fluorene-2-yl}-4-acetyl-aniline), respectively.     

The synthesis,photophysical properties and fluoride anion recognition of a novel branched organoboron compound

A novel two-branched organoboron compound, N,N-bis(7-dimesitylboryl-9,9-diethyl-9H-fluorene-2-yl)aniline, containing a phenylamino group as a π-electron donor, fluorene groups as π-bridges and dimesitylboryl groups as electron acceptors, was synthesized and its photophysical properties in various solvents as well as its fluoride anion recognition properties were investigated. The synthesised compound exhibited strong fluorescence in all solvents with the fluorescence changing from blue to orange on going from solvents of low polarity to those of high polarity. The compound was able to recognize fluoride anions in high sensitivity owing to strong interactions between boron atoms and fluoride anions.     

The third-order nonlinear optical properties of novel styryl dyes

The third-order nonlinear optical properties of two novel styryl dyes, namely, 1,3-diethyl-5-(4-methoxybenzylidene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione and 5-(3,4-dimethoxybenzylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione were studied using the Z-scan technique employing 7 ns laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of effective third-order susceptibility and coupling factor were determined. The optical power limiting behavior of the colorants was ascribed to two-photon absorption phenomenon. Nonlinear absorption cross-section increased with increase in π electron density and the effective two-photon absorption cross-section was two orders of magnitude larger than those of commercially available azo compounds. The results suggest that these colorants offer promise as nonlinear optical materials for device applications.     

The facile synthesis of novel phenothiazine derivatives for blue,yellow-green,and red light emission

Two blue emitters, 3,7-bis(5′-(trifluoromethyl)-1′H-pyrazole-3′-yl)10-ethylphenothiazine and 3,7-bis(5′-(phenyl)-1′H-pyrazole-3′-yl)10-ethyl-phenothiazine and one red, bis-dioxaborine emitter, each based on two, yellow-green emitting, bis-β-diketonate, phenothiazine derivatives, were obtained in high yield and characterized. Systematic investigation of the two-photon absorption characteristics was carried out using one-photon absorption, one-photon excited fluorescence as well as two-photon excited fluorescence spectra. TDDFT computational studies were undertaken to secure an insight into the nature of the compounds' electrochemical and photophysical properties. Low-energy absorption transmissions resemble those observed for the experimental one-photon absorption spectra.     

The synthesis and optical properties of quinoxalines bearing 2,2′:6′,2″-terpyridine

4′-(4-{2-[6,7-Bis-dodecyloxy-3-(2-substituted-phenyl-vinyl)-quinoxalin-2-yl]-vinyl}-phenyl)-[2,2′:6′,2″]terpyridine was prepared by the Horner–Wadsworth–Emmons reaction of 4-[2,2′:6′,2″]terpyridin-4′-yl-benzaldehyde with various quinoxaline derivatives. The absorption and fluorescence maxima of the compounds were observed at 398–443 nm and 484–586 nm, respectively; the compounds offer potential as optical sensors for protons and metal ions.     

比率型过氧化氢荧光探针的合成及成像应用

采用6-甲氧基苯并噻唑-2-羟基喹啉作为双光子荧光团、硼酸酯作为过氧化氢（H2O2）识别基团，合成比率型检测H2O2的双光子荧光探针{6-甲氧基-2-[6-(4,4,5,5-四甲基-1,3,2-二氧硼杂环戊烷-2-基)喹啉-2-基]苯并[d]噻唑}（MQH2O2）。利用荧光光谱和双光子荧光光谱对探针进行H2O2响应能力的评估，结果显示探针具有良好的H2O2比率响应（30 min内比率信号增强约25.4倍、检出限低至38.6 nmol/L）和双光子性质（最大双光子荧光活性截面为150 GM）。通过双光子共聚焦成像完成了细胞和大脑组织成像，结果表明该探针能够实现脑卒中诱导细胞氧化应激的原位成像分析。     

Synthesis and characterization of new imidazole and fluorene–bisphenol based polyamides: Thermal,photophysical and antibacterial properties

A new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy] phenyl}fluorene (III), bearing fluorene–bisphenol and two ortho-linked diaryl-substituted imidazole rings were synthesized by the catalytic reduction of the nitro groups of compound (II), 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-nitrophenoxy]phenyl}fluorene, by using hydrazine monohydrate in the presence of Pd/C. Compound (II) was synthesized by the nucleophilic chloro displacement reaction of the synthesized 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole with 9,9-bis(4-hydroxyphenyl)fluorene in refluxing DMAc in the presence of potassium carbonate. This diamine was condensed directly with aliphatic and aromatic diacids via the Yamazaki–Higashi phosphorylation method in the presence of triphenylphosphite (TPP), pyridine (Py) and halide salt to give high molecular polyamides (PAs). The synthesized PAs were obtained in quantitative yields with inherent viscosities between 0.51 and 0.76 dL g^?1. The structures of diamine and PAs were characterized by elemental analysis, FT-IR and NMR spectroscopy, and properties of PAs were investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and UV–visible and fluorescence spectroscopy. The PAs showed good solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition temperatures (T_gs) and 10% weight loss temperatures (T_10%) in the range of 226–330 °C and 400–466 °C in air, respectively, and fluorescence emission with maximum wavelengths (λ_em) in the range of 417–473 nm with quantum yields (Φ_f) of 9–35%. Two of these polymers together with compounds (II) and (III) were also screened for antibacterial activity against Gram positive and Gram negative bacteria.     

The synthesis and characterization of photonic materials composed of substituted fluorene donors and a porphyrin acceptor

Three novel porphyrin derivatives namely 5,10,15,20-tetra-[7-cyanophenyl-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin, 5,10,15,20-tetra-[7-(4-acetylphenyl)-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin and 5,10,15,20-tetra-[7-pyrenyl-9,9’-bis-(2-ethylhexyl)fluoren-2-yl]-porphyrin were synthesized. Substitution of the aryl groups on the meso-fluorene using Suzuki-Miyaura coupling enabled a study to be undertaken of the energy transfer from the meso fluorenyl to the porphyrin core. To calculate the extent of energy transfer, the corresponding model fluorene compounds 7-cyanophenyl-9,9’-bis-(2-ethylhexyl)fluorene, 7-acetylphenyl-9,9’-bis-(2-ethylhexyl)fluorene and 7-pyrenyl-9,9’-bis-(2-ethylhexyl)fluorene were also synthesized. Fluorescence studies of both the porphyrin derivatives and model compounds showed efficient energy transfer occured from the aryl-fluorene donor to the porphyrin acceptor. Upon excitation, due to energy transfer, a characteristic porphyrin emission was observed at ∼656 nm; ∼99% energy transfer in solution was observed in these donor–acceptor systems. Thin-film emission results indicate a low degree of aggregation in the donor–acceptor systems.     

Synthesis and two-photon absorption properties of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3-N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl₃ have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10⁻⁴⁸ cm⁴ s photon⁻¹ and 66 × 10⁻⁴⁸ cm⁴ s photon⁻¹. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.     

2,5-二氰基-1,4-二(4′-甲氧基苯乙烯基)苯的合成和非线性光学性质

报道了具有典型D-A-D型共轭结构的反式2,5-二氰基-1,4-二(4′-甲氧基苯乙烯基)苯(DCHO)的合成。用核磁、红外和元素分析进行了表征。测试了紫外吸收光谱、单光子荧光光谱、双光子荧光光谱及双光子吸收截面。在800 nm的飞秒脉冲激光激发下,标题化合物发出很强的绿色上转换荧光。化合物2,5-二氰基-1,4-二(4′-甲氧基苯乙烯基)苯的最大吸收波长、单光子发射波长、最大双光子荧光波长、荧光量子产率、双光子吸收系数及双光子吸收截面分别是393 nm、470 nm、475 nm、0.12、0.8 cm/GW、270 GM。这些数据表明,对位甲氧基的D-A-D型化合物具有较好的双光子吸收性能,DCHO是双光子荧光显微与成像应用的一个良好的候选材料。     

Cooperative enhancement of two-photon absorption based on electron coupling in triphenylamine-branching chromophore

Two novel, triphenylamine derivatives N-(4-(4-(diphenylamino)styryl)phenyl)acetamide and N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl)acetamide were synthesized. The two-photon absorption of N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl) was 17-fold greater relative to N-(4-(4-(diphenylamino)styryl)phenyl)acetamide. Linear absorption spectra, steady-fluorescence and time-resolved fluorescence spectra revealed that electron coupling originating from π-electron delocalization is responsible for the strong cooperative enhancement of TPA within the compounds. This is confirmed by the Lippert-Mataga equation.     

Preparation and characterization of novel grafted polyethylene based azo-polymers bearing oligo(ethylene glycol) spacers

Novel grafted azo-polymers were prepared from commercial low density polyethylene plates (PE). First, precursor polymers were synthesized by reacting PE in the presence of acryloyl chloride using gamma radiation. Further esterification of the resulting grafted polymers with four new amino-nitro substituted azobenzene derivatives bearing oligo(ethylene glycol) segments: N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(5-hydroxy-3-oxapentas-1-yl)amine (RED-PEG-2), N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(8-hydroxy-3,6-dioxaoctas-1-yl)amine (RED-PEG-3), N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(11-hydroxy-3,6,9-trioxaundecas-1-yl)amine (RED-PEG-4) and N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(17-hydroxy-3,6,9,12,15-pentaoxaheptadecas-1-yl)amine (RED-PEG-6) led to the formation of branched azo-polymers. These polymers were characterized and their thermal and optical properties were studied. Besides, the influence of the irradiation dose, irradiation time and the structure of the dyes on the properties of the obtained polymers are discussed.     

Synthesis of highly fluorescent coumarinyl chalcones derived from 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and their spectral characteristics

A series of novel coumarin based chalcones were synthesized by the classical crossed aldol condensation reaction of 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and various substituted benzaldehydes. These novel ketocoumarin derivatives having a 1,4-diethyl-1,2,3,4-tetrahydroquinoxaline framework exhibited brilliant fluorescence. The novel chalcones absorbed in the range of 458-523 nm in various solvents. The wavelength of maximum absorption of these chalcones was found to be significantly longer than their simple acyl derivative known in the literature. The dyes displayed longer wavelength of absorption in the high polarity solvents compared to non-polar solvents. Thermogravimetric analysis of the chalcones revealed that the chalcones possess good thermal stability.     

Two-photon absorption properties of push–pull oxazolones derivatives

New fluorescent oxazolone derivatives with high two-photon absorption cross-section were synthesized. Electron donor (phenyl, dimethylaniline and furanyl) and acceptor (nitrobenzene and ethenyl-phenyl-benzimidazol) groups have been appended to the methylene end of 4-(methylidene)-2-phenyl-1,3-oxazol-5(4H)-one in order to produce an highly conjugated π-system with push–pull geometry. The linear and nonlinear optical properties of the oxazolones have been determined. The compounds with a high charge transfer from the substituent group to the oxazolone ring have relatively high two-photon absorption cross-sections (80–100 GM). The best performing nonlinear fluorophore being the benzimidazol derivative with a two-photon absorption cross-section of 80 GM and a relatively high emission quantum yield, ϕ = 0.31.     

Synthesis of phenanthroline derivative by Suzuki coupling reaction and the use of its ruthenium complex as an optical pH sensor

A phenanthroline derivative, which has an aniline group, was synthesized by palladium catalyzed Suzuki cross coupling reactions. The aryl phosphine ligand, PPh_3, showed higher activity than the alkyl phosphines, P(^tBu)₃ and PCy_3, in the Suzuki couplings and provided the coupled product, 4-phenyl-7-(4′-amino-biphenyl-4-yl)-[1,10]phenanthroline (5), with 73% yield. Its ruthenium complex, bis(4,7-diphenyl-[1,10]phenanthroline){4-phenyl-7-(4′-amino-biphenyl-4-yl)-[1,10]phenanthroline} ruthenium(II) bis(hexafluorophosphate) (8), was synthesized under mild conditions. This complex showed a linear fluorescence intensity response between pH 3.5 and pH 8.5.     

Synthesis and characterization of Cu(I) and Zn(II) complexes with new sulfur-bearing isoxazole- or pyrazole-based ligands

The synthesis of the new ligands 6-(5-methyl-1,2-oxazol-3-yl)-2,3-dihydro-5H-[1,4] dithiino[2,3-c]pyrrole-5,7(6H)-dione (isox′) and 6-(3-methyl-1H-pyrazol-5-yl)-2,3-dihydro-5H-[1,4]dithiino[2,3-c]pyrrole-5,7(6H)-dione (pyraz′) and their coordination chemistry toward Cu(I) and Zn(II), was studied. The ligands and their complexes were characterized using a combination of either multinuclear NMR (¹H and ¹³C{¹H}), HRMS, FTIR or Uv–Vis spectroscopy. The solid state structures of ligand isox′ and complexes [Cu(pyraz′)₂]OTf and [Zn(OOCCF₃)₂(pyraz′)₂] were determined. Interestingly, isox′ presents a yellow luminescence in its free form. Additionally, the ability of isox′ to coordinate as an N–O bidentate ligand or as an N–S bridge between two copper centers, forming a coordination polymer, is studied. The solid state structure of this Cu(I)-isox′ 1D coordination polymer is also reported.     

Novel (Phenothiazinyl)Vinyl-Pyridinium Dyes and Their Potential Applications as Cellular Staining Agents

We report here the synthesis and structural characterization of novel cationic (phenothiazinyl)vinyl-pyridinium (PVP) dyes, together with optical (absorption/emission) properties and their potential applicability as fluorescent labels. Convective heating, ultrasound irradiation and mechanochemical synthesis were considered as alternative synthetic methodologies proficient for overcoming drawbacks such as long reaction time, nonsatisfactory yields or solvent requirements in the synthesis of novel dye (E)-1-(3-chloropropyl)-4-(2-(10-methyl-10H-phenothiazin-3-yl)vinyl)pyridin-1-ium bromide 3d and its N-alkyl-2-methylpyridinium precursor 1c. The trans geometry of the newly synthesized (E)-4-(2-(7-bromo-10-ethyl-10H-phenothiazin-3-yl)vinyl)-1-methylpyridin-1-ium iodide 3b and (E)-1-methyl-4-(2-(10-methyl-10H-phenothiazin-3-yl)vinyl)pyridin-1-ium tetrafluoroborate 3a′ was confirmed by single crystal X-ray diffraction. A negative solvatochromism of the dyes in polar solvents was highlighted by UV-Vis spectroscopy and explanatory insights were supported by molecular modeling which suggested a better stabilization of the lowest unoccupied molecular orbitals (LUMO). The photostability of the dye 3b was investigated by irradiation at 365 nm in different solvents, while the steady-state and time-resolved fluorescence properties of dye 3b and 3a′ in solid state were evaluated under one-photon excitation at 485 nm. The in vitro cytotoxicity of the new PVP dyes on B16-F10 melanoma cells was evaluated by WST-1 assay, while their intracellular localization was assessed by epi-fluorescence conventional microscopy imaging as well as one- and two-photon excited confocal fluorescence lifetime imaging microscopy (FLIM). PVP dyes displayed low cytotoxicity, good internalization inside melanoma cells and intense fluorescence emission inside the B16-F10 murine melanoma cells, making them suitable staining agents for imaging applications.     

Phosphorescent,green-emitting Ir(III) complexes with carbazolyl-substituted 2-phenylpyridine ligands: Effect of binding mode of the carbazole group on photoluminescence and electrophosphorescence

The ligands, 9-((6-phenylpyridin-3-yl)methyl)-9H-carbazole and 9-(4-(pyridin-2-yl)benzyl)-9H-carbazole were synthesized by attaching a carbazolyl group to the pyridine and phenyl rings of 2-phenylpyridine, respectively. Ir(III) complexes were prepared by a simple procedure and the solubility of the novel complexes was significantly better than that of the conventional, green-emitting conventional fac-tris(2-phenylpyridinato-C²,N)iridium(III). The Ir(III) complexes were used to prepare electrophosphorescent polymer light-emitting devices. The device comprising 10% of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C²,N)iridium(III) exhibited an external quantum efficiency of 7.88%, luminous efficiency of 23.01 cd/A, and maximum brightness of 32,640 cd/m². The color of the emissions of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C²,N)iridium(III) was similar to that of conventional fac-tris(2-phenylpyridinato-C²,N)iridium(III). This work shows that integration of a rigid hole-transporting carbazole and phosphorescent complex in one molecule provides a new route to highly efficient, solution-processable complexes for electrophosphorescent applications.     

Optical properties and aggregation of novel azo-dyes bearing an end-capped oligo(ethylene glycol) side chain in solution,solid state and Langmuir–Blodgett films

Optical properties and aggregation of two novel azo-dyes N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(3,6,9-trioxadecas-1-yl)amine (RED-PEGM-3) and N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl] phenyl}-N-(3,6,9,12,15,18,21,24-octaoxapentaeicos-1-yl)amine (RED-PEGM-8) were studied by UV–vis spectroscopy in solution, solid state and Langmuir–Blodgett films. The results were compared to those obtained for their precursor 1-amino-4′-nitroazobenzene (Disperse Orange 3, DO3) and 1-N-methylamino-4′-nitroazobenzene (RED-H). Increasing the polarity of methanol:water mixtures gave rise to the formation of H-aggregates for all dyes. Similar aggregates were also detected in cast films. NOESY, 2D ¹H NMR experiments carried out in aqueous solutions of RED-PEGM-8 revealed the formation of atypical antiparallel H-aggregates. Only RED-PEGM-3 gave traces of J-aggregates in the solid state. RED-PEGM-3 and RED-PEGM-8 readily form J-aggregates in Y-type Langmuir–Blodgett films.     

Azomethine coupled fluorene–thiophene–pyrrole based copolymers: Electrochromic applications

Two new copolymers were synthesized via the electrochemical copolymerization of 4,4′-(9H-fluorene-9,9-diyl)bis(N-(thiophen-2-ylmethylene)aniline) (FTMA) with thiophene (Th) and pyrrole (Py). According to the X-ray Photoelectron Spectroscopy (XPS) measurements, the polymers FTMA-co-Th and FTMA-co-Py possessed monomer ratios of nearly 1/5 (FTMA/Th) and 1/2 (FTMA/Py). Spectroelectrochemical investigations showed that FTMA-co-Th was a red color at low potentials and a blue color at high potentials. FTMA-co-Py was purple at low potentials and dark gray at high potentials. Spectroelectrochemical monitoring showed good absorption recoveries over repeated potential scans. As a result, FTMA-co-Th and FTMA-co-Py may be good candidates for electrochromic devices (ECDs) and could be used as coloring agents in electrochromic layers in ECDs.