Enhanced Catalytic Activity and Unexpected Products from the Oxidation of Cyclohexene by Organic Nanoparticles of 5,10,15,20‐Tetrakis‐(2,3,4,5,6‐pentafluorophenyl)porphyrinatoiron(III) in Water by Using O2

The catalytic oxidation of alkenes by most iron porphyrins using a variety of oxygen sources, but generally not dioxygen, yields the epoxide with minor quantities of other products. The turnover numbers for these catalysts are modest, ranging from a few hundred to a few thousand depending on the porphyrin structure, axial ligands, and other reaction conditions. Halogenation of substituents increases the activity of the metalloporphyrin catalyst and/or makes it more robust to oxidative degradation. Oxidation of cyclohexene by 5,10,15,20‐tetrakis‐(2,3,4,5,6‐pentafluorophenyl)porphyrinato iron(III), ([Fe^III(tppf₂₀)]) and H₂O₂ is typical of the latter: the epoxide is 99 % of the product and turnover numbers are about 350. 1 – 4 Herein, we report that dynamic organic nanoparticles (ONPs) of [Fe^III(tppf₂₀)] with a diameter of 10 nm, formed by host–guest solvent methods, catalytically oxidize cyclohexene with O₂ to yield only 2‐cyclohexene‐1‐one and 2‐cyclohexene‐1‐ol with approximately 10‐fold greater turnover numbers compared to the non‐aggregated metalloporphyrin in acetonitrile/methanol. These ONPs facilitate a greener reaction because the reaction solvent is 89 % water and O₂ is the oxidant in place of synthetic oxygen sources. This reactivity is unexpected because the metalloporphyrins are in close proximity and oxidative degradation of the catalyst should be enhanced, thus causing a significant decrease in catalytic turnovers. The allylic products suggest a different oxidative mechanism compared to that of the solvated metalloporphyrins. These results illustrate the unique properties of some ONPs relative to the component molecules or those attached to supports.     

Organic nanoparticles for electrogenerated chemiluminescence assay

Organic nanoparticles (ONPs) are one type of nanoparticles assembled by the organic compounds with one dimension smaller than 100 nm. ONPs are alternative nanomaterials in organic light-emitting diode and analytical applications due to their unique optical and electrochemical properties. In electrogenerated chemiluminescence (ECL) assays, ONPs are generally taken as signal reporters for chemical sensing and biosensing. In this opinion, we focus on recent developments of ONPs as ECL luminophores in analytical application. The types and ECL mechanisms of ONPs systems and the approaches of ONPs-based ECL methods are briefly introduced. New advances on the improvement of the ECL efficiency of ONPs are highlighted. The challenges and perspectives of ONPs-based ECL methods are discussed.     

Multiresidue analysis of three groups of pesticides in washing waters from olive processing by solid-phase extraction-gas chromatography with electron capture and thermionic specific detection

A multiresidue solid phase extraction-gas chromatography (SPE-GC) method is developed for the analysis of 28 organochlorine (OCPs), organophosphorus (OPPs) and organonitrogen (ONPs) pesticides at ng l^− 1 levels in washing water from olive processing. Pesticides are separated from the water matrix, containing estimable amounts of olive oil, by eluting them from a C₁₈ SPE cartridge using dichloromethane. The target compounds are determined in the final extract by gas chromatography using thermionic specific (TSD) and electron capture (ECD) detection. Recoveries range from 79% to 129% in spiked washing water samples and detection limits are between 1 and 4 ng l^− 1. The method was successfully applied to determine OCPs, OPPs and ONPs in 25 samples of water collected directly in the inlet and outlet of the washing devices of three olive mills at different locations in Jaén (Spain). The most frequently encountered pesticide residues were terbuthylazine, simazine and diuron. In some of the water samples coming from the inlet of the washing devices, terbuthylazine and diuron measured concentrations were above the concentration limits scheduled by law.     

Synthesis and characterization of poly(1,4‐bis((E)‐2‐(3‐dodecylthiophen‐2‐yl)vinyl)benzene) derivatives

New amorphous semiconducting copolymers, poly(9,9‐dialkylfluorene)‐alt‐(3‐dodecylthienyl‐divinylbenzene‐3‐dodecylthienyl) derivatives (PEFTVB and POFTVB), were designed, synthesized, and characterized. The structure of copolymers was confirmed by H NMR, IR, and elemental analysis. The copolymers showed very good solubility in organic solvents and high thermal stability with high T_g of 178–185 °C. The weight average molecular weight was found to be 107,900 with polydispersity of 3.14 for PEFTVB and 76,700 with that of 3.31 for POFTVB. UV–vis absorption studies showed the maximum absorption at 428 nm (in solution) and 435 nm (in film) for PEFTVB and at 430 nm (in solution) and 436 nm (in film) for POFTVB. Photoluminescence studies showed the emission at 498 nm (in solution) and 557 nm (in film) for PEFTVB and at 498 nm (in solution) and 536 nm (in film) for POFTVB. The solution‐processed thin‐film transistors showed the carrier mobility of 2 × 10^?4 cm² V^?1 s^?1 for PEFTVB‐based devices and 2 × 10^?5 cm² V^?1 s^?1 for POFTVB‐based devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3942–3949, 2010     

Ethynylene‐Linked Oligomers Based on Benzodithiophene: Synthesis and Photoelectric Properties

Two conjugated ethynyl‐linked oligomers, oligo(benzodithiophene‐ethynylene‐benzothiadiazole) (O1) and oligo(benzodithiophene‐ethynylene‐carbazole) (O2), were synthesized by Sonogashira coupling reaction. Their degrees of polymerization were 7 and 10, respectively. Their photophysical and electrochemical properties were investigated. O1 exhibitd two strong absorption bands at 404 nm and 483 nm, and O2 at 401 nm and 429 nm. The results of UV‐Vis, cyclic voltammetry (CV) and theoretical calculations showed that O1 has a narrower band gap than O2. The conductivities of O1 and O2 were 1.05×10^?15 and 6.98×10^?16 S/cm, respectively, and would increase to 1.23×10^?10 and 1.05×10^?10 S/cm after doping with iodine.     

Synthesis,Structural Characterization,Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

A platinum complex with the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl ligand ( 1 ) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low‐lying excited electronic states. Complex 1 exhibits intense structured ¹π–π* absorption at λ_abs<440 nm, and a broad, moderate ¹M LCT/¹LLCT transition at 440–520 nm in CH₂Cl₂ solution. A structured ³π–π*/³M LCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited‐state absorption from 450 nm to 750 nm, which are tentatively attributed to the ¹π–π* and ³π–π* excited states of the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridine ligand, respectively. Z‐scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near‐IR wavelengths. The experimental data were fitted by a five‐level model by using the excited‐state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited‐state absorption cross sections in the visible spectral region and the effective two‐photon absorption cross sections in the near‐IR region. Our results demonstrate that 1 possesses large ratios of excited‐state absorption cross sections relative to that of the ground‐state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH₂Cl₂ solution illuminated by ns laser pulses at 532 nm. The two‐photon absorption cross sections in the near‐IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two‐photon‐assisted excited‐state absorption in the near‐IR region.     

A Diradical Approach towards BODIPY‐Based Dyes with Intense Near‐Infrared Absorption around λ=1100 nm

A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para‐ and meta‐quinodimethane‐bridged BODIPY dimers BD‐1 and BD‐2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm (?=6.65×10⁵ M ^?1 cm^?1) and 1136 nm (?=6.44×10⁵ M ^?1 cm^?1), respectively, together with large two‐photon‐absorption cross‐sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn‐on response in the presence of the hydroxyl radical but not with other reactive oxygen species.     

A Puckered Singlet Cyclopentane‐1,3‐diyl: Detection of the Third Isomer in Homolysis

In the photochemical denitrogenation of 1,4‐diaryl‐2,3‐diazabicyclo[2.2.1]heptane ( AZ6 ) bearing sterically hindered substituents, a curious new absorption band at about 450 nm was observed under low‐temperature matrix conditions, together with the previously well‐characterized planar singlet diradical pl‐¹ DR6 with λ_max=≈580 nm. The 450 nm species was electron paramagnetic resonance (EPR)‐silent. Instead of generating the planar diradical pl‐¹ DR6 and the precursor azoalkane AZ6 upon warming, the ring‐closed bicyclo[2.1.0]pentane derivative SB6 , that is, the AZ6 denitrogenation product was identified. Based on product analysis, low‐temperature spectroscopic observations, high‐level quantum‐mechanical computations, viscosity effect, and laser‐flash photolysis, the puckered singlet diradicaloid puc‐¹ DR6 was assigned to the new 450 nm absorption. The latter was detected experimentally at the same time as the planar singlet diradical pl‐¹ DR6 . Sterically demanding substituents as well as viscosity impediments were essential for the detection of the experimentally hitherto unknown puckered singlet cyclopentane‐1,3‐diyl diradicaloid puc‐¹ DR6 , that is, the third isomer in homolysis. The present findings should stimulate future work on the mechanistically fascinating stereoselectivity documented in the formation of bicyclo[2.1.0]pentanes during the 2,3‐diazabicyclo[2.2.1]heptane denitrogenation.     

Masked Rhodamine Dyes of Five Principal Colors Revealed by Photolysis of a 2‐Diazo‐1‐Indanone Caging Group: Synthesis,Photophysics, and Light Microscopy Applications

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as “hidden” markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2‐diazo‐1‐indanone group can be irreversibly photoactivated, either by irradiation with UV‐ or violet light (one‐photon process), or by exposure to intense red light (λ～750 nm; two‐photon mode). All dyes possess a very small 2‐diazoketone caging group incorporated into the 2‐diazo‐1‐indanone residue with a quaternary carbon atom (C‐3) and a spiro‐9H‐xanthene fragment. Initially they are non‐colored (pale yellow), non‐fluorescent, and absorb at λ=330–350 nm (molar extinction coefficient (ε)≈10⁴ M^?1 cm^?1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511–633 and 525–653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε= 3–8×10⁴ M^?1 cm^?1 and fluorescence quantum yields (?)=40–85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water‐soluble caged red‐emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino‐reactive N‐hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375–420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3–6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (?=20–38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10–40 % of the non‐fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a “dark” non‐emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super‐resolution optical microscopy is exemplified.     

Solid‐State Carbon Dots with Efficient Cyan Emission towards White Light‐Emitting Diodes

Efficient cyan‐emitting solid carbon dots (CDs) were synthesized via a one‐pot hydrothermal method. The obtained solid CDs show a broad absorption from 270–460 nm with a maximum around 400 nm, and emit intense cyan light around 500 nm with an internal photoluminescence quantum efficiency of 34.1 % under 400 nm excitation. The emission maximum of the solid CDs remains unchanged under 320–400 nm excitations. Compared with dilute aqueous of CDs (2.5 mg mL^?1), the emission of solid CDs shows an obvious red‐shift of 50 nm. The red‐shift is caused by resonant energy transfer due to larger spectral overlap and smaller interparticle distance, together with a new surface state caused by aggregation in solid CDs. A lamp with white LEDs was fabricated by dropping a mixture of solid CDs, CaAlSiN₃:Eu²⁺ and silicon resin on the top of a near‐ultraviolet LED chip. Under an operating current of 20 mA, the as‐fabricated white LED generates a high‐quality, warm white light with a color rendering index of 86.1, a color temperature of 4340 K, and a luminescence efficiency of 31.3 lm W^?1.     

Broadband Visible‐Light‐Harvesting trans‐Bis(alkylphosphine) Platinum(II)‐Alkynyl Complexes with Singlet Energy Transfer between BODIPY and Naphthalene Diimide Ligands

A heteroleptic bis(tributylphosphine) platinum(II)‐alkynyl complex ( Pt‐1 ) showing broadband visible‐light absorption was prepared. Two different visible‐light‐absorbing ligands, that is, ethynylated boron‐dipyrromethene (BODIPY) and a functionalized naphthalene diimide (NDI) were used in the molecule. Two reference complexes, Pt‐2 and Pt‐3 , which contain only the NDI or BODIPY ligand, respectively, were also prepared. The coordinated BODIPY ligand shows absorption at 503 nm and fluorescence at 516 nm, whereas the coordinated NDI ligand absorbs at 594 nm; the spectral overlap between the two ligands ensures intramolecular resonance energy transfer in Pt‐1 , with BODIPY as the singlet energy donor and NDI as the energy acceptor. The complex shows strong absorption in the region 450 nm–640 nm, with molar absorption coefficient up to 88 000 M ^?1 cm^?1. Long‐lived triplet excited states lifetimes were observed for Pt‐1 – Pt‐3 (36.9 μs, 28.3 μs, and 818.6 μs, respectively). Singlet and triplet energy transfer processes were studied by the fluorescence/phosphorescence excitation spectra, steady‐state and time‐resolved UV/Vis absorption and luminescence spectra, as well as nanosecond time‐resolved transient difference absorption spectra. A triplet‐state equilibrium was observed for Pt‐1 . The complexes were used as triplet photosensitizers for triplet–triplet annihilation upconversion, with upconversion quantum yields up to 18.4 % being observed for Pt‐1 .     

Synthesis,Structure, Properties,and Application of a Carbazole‐Based Diaza[7]helicene in a Deep‐Blue‐Emitting OLED

A carbazole‐based diaza[7]helicene, 2,12‐dihexyl‐2,12‐diaza[7]helicene ( 1 ), was synthesized by a photochemical synthesis and its use as a deep‐blue dopant emitter in an organic light‐emitting diode (OLED) was examined. Compound 1 exhibited good solubility and excellent thermal stability with a high decomposition temperature (T_d=372.1 °C) and a high glass‐transition temperature (T_g, up to 203.0 °C). Single‐crystal structural analysis of the crystalline clathrate ( 1 )₂ ? cyclohexane along with a theoretical investigation revealed a non‐planar‐fused structure of compound 1 , which prevented the close‐packing of molecules in the solid state and kept the molecule in a good amorphous state, which allowed the optimization of the properties of the OLED. A device with a structure of ITO/NPB (50 nm)/CBP:5 % 1 (30 nm)/BCP (20 nm)/Mg:Ag (100 nm)/Ag (50 nm) showed saturated blue light with Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.10); the maximum luminance efficiency and brightness were 0.22 cd A^?1 (0.09 Lm W^?1) and 2365 cd m^?2, respectively. This new class of helicenes, based on carbazole frameworks, not only opens new possibilities for utilizing helicene derivatives in deep‐blue‐emitting OLEDs but may also have potential applications in many other fields, such as molecular recognition and organic nonlinear optical materials.     

Derivative and Derivative Ratio Spectrophotometric Analysis of Antihypertensive Ternary Mixture of Amiloride Hydrochloride,Hydrochlorothiazide and Timolol Maleate

Two simple, rapid and reliable spectrophotometric methods are described for the resolution of the three‐component mixture of amiloride hydrochloride (AMD), hydrochlorothiazide (HCT) and timolol maleate (TIM). The first method involves the use of derivative spectrophotometry with the zero‐crossing technique where AMD was easily determined using its ⁰D and ¹D(Δλ = 6) amplitudes at 365 and 385 nm, respectively, while HCT and TIM were determined by measuring the ³D(Δλ = 6) amplitude at 265 nm and the ¹D(Δλ = 8) amplitude at 315.4 nm, respectively. The second method involves the application of the ratio‐spectra zero‐crossing first and second derivative spectrophotometry where two points have been used for the quantification of each compound. For the determination of AMD, HCT was used as divisor and the ¹DD (Δλ = 4) and ²DD (Δλ = 6) values at 299.4 and 311 nm, respectively, were plotted against AMD concentration; while — by using TIM as divisor — the ²DD (Δλ = 6) amplitudes at 264.2 and 290 nm were found to be proportional to HCT concentration. TIM was assayed in the mixture using its ¹DD (Δλ = 6) amplitudes at 289.8 nm (Divisor was AMD) and 314.8 nm (Divisor was HCT). Synthetic mixtures of different proportions and laboratory‐made tablets were assayed by the proposed methods and the results revealed good accuracy and repeatability of the developed methods.     

Electronic Characterization of Reaction Intermediates: The Fluorenylium,Phenalenylium, and Benz[f]indenylium Cations and Their Radicals

Three vibrationally resolved absorption systems commencing at 538, 518, and 392 nm were detected in a 6 K neon matrix after mass‐selected deposition of C₁₃H₉⁺ ions (m/z=165) produced from fluorene in a hot‐cathode discharge ion source. The benz[f]indenylium (BfI⁺: 538 nm), fluorenylium (FL9⁺: 518 nm), and phenalenylium (PHL⁺: 392 nm) cations are the absorbing molecules. Two electronic systems corresponding to neutral species are apparent at 490 and 546 nm after irradiation of the matrix with λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 ¹B₂←X̃ ¹A₁ absorption of FL9⁺, and the 490 nm band is the 2 ²A₂←X̃ ²B₁ origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 ¹A₁←X̃ ¹A₁ and 1 ²A₂←X̃ ²A₂ transitions of BfI⁺ and BfI. The 392 nm band is the 1 ¹E′←X̃ ¹A₁′ transition of PHL⁺. The electronic spectra of C₁₃H₉⁺/C₁₃H₉ were assigned on the basis of the vertical excitation energies calculated with SAC‐CI and MS‐CASPT2 methods.     

Electronic Characterization of Reaction Intermediates: The Fluorenylium,Phenalenylium, and Benz[f]indenylium Cations and Their Radicals

Three vibrationally resolved absorption systems commencing at 538, 518, and 392 nm were detected in a 6 K neon matrix after mass‐selected deposition of C₁₃H₉⁺ ions (m/z=165) produced from fluorene in a hot‐cathode discharge ion source. The benz[f]indenylium (BfI⁺: 538 nm), fluorenylium (FL9⁺: 518 nm), and phenalenylium (PHL⁺: 392 nm) cations are the absorbing molecules. Two electronic systems corresponding to neutral species are apparent at 490 and 546 nm after irradiation of the matrix with λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 ¹B₂←X? ¹A₁ absorption of FL9⁺, and the 490 nm band is the 2 ²A₂←X? ²B₁ origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 ¹A₁←X? ¹A₁ and 1 ²A₂←X? ²A₂ transitions of BfI⁺ and BfI. The 392 nm band is the 1 ¹E′←X? ¹A₁′ transition of PHL⁺. The electronic spectra of C₁₃H₉⁺/C₁₃H₉ were assigned on the basis of the vertical excitation energies calculated with SAC‐CI and MS‐CASPT2 methods.     

The Dewar Isomer of 1,2‐Dihydro‐1,2‐azaborinines: Isolation,Fragmentation, and Energy Storage

The photochemistry of 1,2‐dihydro‐1,2‐azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and an iminoborane derivative. The thermal electrocyclic ring‐opening reaction of the Dewar valence isomer back to the 1,2‐dihydro‐1‐tert‐butyldimethylsilyl‐2‐mesityl‐1,2‐azaborinine has an activation barrier of (27.0±1.2) kcal mol⁻¹. In the presence of the Wilkinson catalyst, the ring opening occurs rapidly and exothermically (ΔH=(−48±1) kcal mol⁻¹) at room temperature.     

A Red‐Emissive Sextuple Hydrogen‐Bonding Self‐Assembly Molecular Duplex Bearing Perylene Diimide Fluorophores for Warm‐White Organic Light‐Emitting Diode Application

A novel sextuple hydrogen‐bonding (HB) self‐assembly molecular duplex bearing red‐emitting perylene diimide (PDI) fluorophores, namely PDIHB , was synthesized, and its molecular structure was confirmed by ¹H NMR, ¹³C NMR, TOF‐MS and 2D NMR. Compared with the small molecular reference compound PDI , PDIHB shows one time enhanced fluorescence efficiency in solid state (4.1% vs. 2.1%). More importantly, the presence of bulky HB oligoamide strands in PDIHB could trigger effective spatial separation between guest and host fluorophores in thin solid film state, hence inefficient energy transfer occurs between the blue‐emitting host 2TPhNIHB and red guest PDIHB in the 2 wt% guest/host blending film. As a result, a solution‐processed organic light‐emitting diode (OLED) with quite simple device structure of ITO/PEDOT:PSS (40 nm)/PVK (40 nm)/ PDIHB (2 wt%): 2TPhNIHB (50 nm)/LiF (0.8 nm)/Al (100 nm) could emit bias‐independent warm‐white electroluminescence with stable Commission Internationale de L'Eclairage coordinates of (0.42, 0.33), and the maximum brightness and current efficiency of this device are 260 cd·m^?2 and 0.49 cd·A^?1, respectively. All these results indicated that HB self‐assembly supramolecular fluorophores could act as prospective materials for white OLED application.     

Photoreduction of Azaoxoisoaporphines by Amines: Laser Flash and Steady‐State Photolysis and Pulse Radiolysis Studies

Photoreduction of 7H‐benzo[e]perimidin‐7‐one (3‐AOIA, A1) and its 2‐methyl derivative (2‐Me‐3‐AOIA, A2) by non‐H‐donating amines (1,4‐diazabicyclo[2.2.2]octane [DABCO]; 2,2,6,6‐tetramethylpiperidine [TMP]), and a hydrogen‐donating amine (triethylamine [TEA]), has been studied in deaerated neat acetonitrile solutions using laser flash photolysis (LFP) and steady‐state photolysis. The triplet excited states of A1 and A2 were characterized by a strong absorption band with λ_max = 440 nm and lifetimes of 20 and 27 μs respectively. In the presence of tertiary amines, both triplet excited states were quenched with rate constants close to the diffusional limit (k_q ranged between 10⁹ and 10¹⁰ M^?1 s^?1). The transient absorption spectra observed after quenching with DABCO and TMP were characterized by maxima located at 460 nm and broad shoulders in the range of 500–600 nm. These transient species are attributed to solvent‐separated radical ion pairs and/or to isolated radical anions. In the presence of TEA, these transients undergo proton transfer, leading to the neutral hydrogenated radicals, protonated over the N1‐ and O‐atoms. Transient absorption spectra of these transients were characterized by maxima located at 400 and 520 nm and 430 nm respectively. Additional support for these spectral assignments was provided by pulse radiolysis (PR) experiments in acetonitrile and 2‐propanol solutions.     

The Synthesis,X‐ray Structure Analysis,and Photophysical Characterization of 4‐[(E)‐2‐(4‐Carboxyphenyl)diazenyl]‐morpholine

4‐[(E)‐2‐(4‐Carboxyphenyl)diazenyl]‐morpholine ( 1 ) was prepared in 33% yield from a coupling reaction between morpholine and the diazonium ion formed from 4‐aminobenzoic acid. X‐ray structural analysis of 1 yielded two important insights into its structure: the geometry of the N―N double bond and the partial delocalization across the linear triazene moiety. The absorption spectra of 1 in dilute acetonitrile and 2‐methyltetrahydrofuran solutions both featured an intense (ε ≈ 20,000 M^?1cm^?1) band centered at 320–324 nm that was assigned as a mixture of π → π* and n → π* transitions. Emission was observed at 383 and 379 nm from dilute acetonitrile and 2‐methyltetrahydrofuran solutions of 1 , respectively, with the latter being red‐shifted to 439 nm at 77 K. Emission lifetime data for compound 1 provided evidence that the emission was a mixture of two excited state transitions.     

Ultrathin pH‐Sensitive Nanoporous Membranes for Superfast Size‐Selective Separation

Stimuli‐responsive nanoporous membranes have attracted increasing interest in various fields due to their abrupt changes of permeation/separation in response to the external environment. Here we report ultrathin pH‐sensitive nanoporous membranes that are easily fabricated by the self‐assembly of poly(acrylic acid) (PAA) in a metal hydroxide nanostrand solution. PAA‐adsorbed nanostrands (2.5–5.0 nm) and PAA‐Cu^II nanogels (2.0–2.5 nm) grow competitively during self‐assembly. The PAA‐adsorbed nanostrands are deposited on a porous support to fabricate ultrathin PAA membranes. The membranes display ultrafast water permeation and good rejection as well as significant pH‐sensitivity. The 28 nm‐thick membrane has a water flux decrease from 3740 to 1350 L m^?1 h^?1 bar^?1 (pH 2.0 to 7.0) with a sharp decrease at pH 5.0. This newly developed pH‐sensitive nanoporous membranes may find a wide range of applications such as controlled release and size‐ and charge‐selective separation.