Spectroelectrochemical studies of poly-o-phenylenediamine Part 2. In situ UV—vis subtractive reflectance spectroscopy

In our previous paper, the phenazine-like structure of the poly-o-phenylenediamine (PoPD) and its three steady redox states have been revealed mainly by using in situ resonance Raman spectroscopy. It has also been shown that the semi-oxidized state of PoPD is the most stable state of PoPD, while the totally-oxidized state of PoPD is chemically unstable and can exist only at certain electrode potentials. In the present work, the more detailed reaction mechanism of a PoPD film in strong acid solution has been studied by using in situ UV—vis substractive reflectance spectroscopy. The semi-oxidized state and the totally-oxidized state of PoPD have electronic absorption bands around 300 nm, 430 nm, 500 nm and 300 nm, 450 nm, 530 nm, 735 nm respectively in the in situ steady state UV—vis subtractive reflectance spectra with respect to the reduced state of PoPD, which verifies once again that three redox states of PoPD exist in the redox process of PoPD. Moreover, the relative intensity between two oxidized states of PoPD at the maximum absorption wavelength (λ_max) reveals that only about one third of the semi-oxidized state of PoPD can be oxidized to the totally-oxidized state of PoPD. The in situ resonance Raman spectra and the cyclic voltammograms of PoPD display the same quantitative relationship. New absorption bands were observed in the in situ time-resolved UV—vis subtractive reflectance spectra with appropriate time resolutions, which illustrate the dynamic structure changes of PoPD in its redox process. These intermediate states of PoPD are more unstable than its three redox states.     

Indirect Photo-Induced Phosphorylation Via a C-Ester Caged Troika Acid

Abstract

Use of a photoremovable “caging” group allows the generation of reactive molecules under mild conditions. Photo-induced phosphorylations typically have involved attachment of the photosensitive group at phosphorus.[1] We now have investigated indirect photolytic activation of an unmodified phosphonic acid group using broad band UV (Hg lamp), 308 nm XeCl excimer laser or 355 nm YAC laser irradiation of the o-nitrobenzyl C-ester of “troika acid” [(E)-1²]. In alcohols or neutral buffer, irradiation of (E)-2 gave phosphorylation of the solvent plus phosphorocyanidate, the expected 2-isomer product.²All thrce UV sources gave -1:2 E:Z product distribution in MeOH. In the (E)-1 methyl C-ester, the oxime functionality absorbed strongly near 205 nm (E_max 5200), weakly at 308 nm and negligibly above 355 nm, and no photoisomerization was seen using the 355 nm source. Thus, oxime isomerization in (E)-2 at least using 355 nm irradiation. requires the o-nitrobenzyl group, and possibly involves an energy- or charge-wansfer effect. Phosphorylation of EtOH/t-BuOH mixtures by photolysis of (E)-2 showed little alkyl selectivity. consistent with photoinduced formation of an intermediate. plausibly (E)-1, which undergoes spontaneous dissociative fragmentation via a monomeric metaphosphate-like species.     

Photorelease of alcohols from 2-nitrobenzyl ethers proceeds via hemiacetals and may be further retarded by buffers intercepting the primary aci-nitro intermediates

The mechanism for the photoinduced release of glycolic acid from its 2-nitrobenzyl ether was reinvestigated. The pH-dependent rate constants of the thermal reactions initiated by irradiation are similar to those reported previously for 2-nitrobenzyl methyl ether. A hemiacetal intermediate that limits the release rate of glycolic acid at pH values 相似文献   

Synthesis of (±)-laudanoeine and a study of 1-benzyl-3-isoquinoione intermediates

A keto acid (2) has been converted to tetrahydropapaverine and (±)-laudanosine. Some intermediate 3-isochromanone ( 3 ) and 3-isoquinolone ( 4 and 5 ) derivatives have been investigated and structures assigned to these compounds from spectroscopic studies. The 3-isoquinolone tautomer with the o-quinonoid structure predominates over the 3-isoquinolinol form, but the analogous oxygen derivative has preferentially a stilbene structure ( 3 ) with an intact benzene system.     

A Study of Spectroscopy on TCAQ Microcrystal

UV-visible absorption spectra of 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) solution, crystal and evaporated film were, measured. The absorption spectrum of TCAQ solution in DMF had three bands at 287 nm(4.45), 310 nm(4.23) and 350 nm(4.38) respectively; that of evaporated films had one band at 370 nm and that of crystalline powder had four bands at 243 nm, 275 nm, 320 nm and 430 nm respectively. Surface photovoltage spectra of TCAQ microcrystal gave two bands at P₁ (320 nm) and P₂ (430 nm) respectively. The absorption bands were assigned and the energy levels of frontier orbitals were tentatively determined. In addition,the mechanism of hole, production and transportation in crystalline TCAQ was discussed.     

Synthesis and crystal structure of copper complex of 7,16-bis(2-hydroxy-5-methyl-3-nitrobenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane

A lariat crown ether compound 7,16-bis(2-hydroxy-5-methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane has been prepared via one-pot Mannich reaction. A copper(II) complex with the ligand 7,16-bis(2-hydroxy-5-methyl-3-nitrobenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane was unexpectedly synthesized and characterized by elemental analysis, IR and UV spectra. The crystal structure of the complex has been determined by X-ray diffraction. Both crystal structure analysis and spectroscopy study indicated that the side-arm phenols of lariat crown ether are nitrated while complexing with Cu(NO₃)₂. Structure shows that the copper(II) ion is coordinated to two nitrogen and four oxygen atoms, two from the crown ether and other two from the deprotonated phenolate groups. The coordination polyhedron is a distorted octahedron.     

Identification of some isomeric [C8H6O]+˙ ions generated from phenyl substituted cyclic ketones using collisional activation

[C₈H₆O]⁺˙ ions with o-quinonoid ketene, benzocyclobutenone, phenyl ketene and benzofuran structures have been generated from various precursors. Their collisionally induced decompositions in both field free regions of a double focusing mass spectrometer with so-called reversed geometry have been studied using mass analysed ion kinetic energy scans and B/E linked scans. In both cases the abovementioned [C₈H₆O]⁺˙ structures can be distinguished–except the benzocyclobutenone ion which gives very similar spectra to the o-quinonoid ion–on the basis of the intensity ratios [m/z 77]/[m/z 76] and [m/z 104]/[m/z 102]. The stable [C₈H₆O]⁺˙ ions generated from the molecular ions of 7 -phenylbicyclo[3.1.1]heptan-6-one appear to have the phenyl ketene structure, as was suspected from previous kinetic energy release measurements.     

Synthesis and spectroscopic studies of novel transition metal complexes with schiff base synthesized from 1,4-bis-(<Emphasis Type="Italic">o</Emphasis>-aminophenoxy)butane and salicyldehyde

The new Co(II), Cu(II), Ni(II) and Zn(II) complexes of potentially N₂O₂ Schiff base ligand [N,N’-bis(salicyldehydene)-1,4-bis-(o-aminophenoxy)butane] (H₂L) prepared from 1,4-bis-(o-aminophenoxy)butane and salicyldehyde in DMF. Microanalytical data, elemental analysis, magnetic measurements, ^lH NMR, ¹³C NMR, UV-visible and IR spectra as well as conductance measurements were used to confirm the structures. In all complexes, H₂L behaves as a tetradentate. The article is published in the original.     

Photopolymerization of cyclohexene oxide by use of o-nitrobenzyl triphenylsilyl ether/aluminum compound catalyst. Dependence of catalyst activity on the structure of the silyl ether

o-Nitrobenzyl triphenylsilyl ehther/aluminum compound has been previously shown by the authors to act as catalyst in the photopolymerization of epoxides. The dependence of the structure of the silyl ether on the catalyst activity was examined. There were two steps in the photopolymerization. The first step (“Step 1”) is photodecomposition of the silyl ether to silanol. The second step (“Step 2”) is the initiation of polymerization by silanol and the aluminum compound. The introduction of an electron withdrawing group, Cl, CF₃, on the benzene ring bonded to Si made the quantum yield of Step 1 low, however, the rate of Step 2 was increased. The low quantum yield of Step 1 was explained in terms of the rate of electron transfer that is controlled by the relative electron density between the CH₂ and NO₂ in the o-nitrobenzyl group. The acceleration of Step 2 was explained in terms of an increase in silanol acidity that was promoted by the introduction of an electron withdrawing group. The overall rate of the photopolymerizatiol depends to a greater degree on the rate of Step 2 than on that of Step 1.     

A Coordination-Induced 1,4→1,2-Quinonediimine Isomerization

Hitherto unused in coordination compounds , the para-quinonoid azophenine (p-ap) has now been applied for the synthesis of [Cu(PPh₃)₂(o-ap)](BF₄) ( 1 ), in which the ligand exists as its ortho-quinonoid tautomer. Additional stabilization of this metal–π donor/ligand–π acceptor arrangement occurs through chelate-like hydrogen bonding between the NH functionalities, which are both now ortho-positioned, and the BF₄⁻ counterion.     

激光诱导的亚硝酸与二苯醚的反应机理

355 nm光照下利用瞬态吸收光谱技术进行了有氧、无氧条件下二苯醚与亚硝酸体系的反应机理研究, 考察了其中瞬态物种的衰减行为, 并对其光解产物进行了GC-MS分析. 研究表明, HNO₂在355 nm紫外光的照射下产生的OH自由基和二苯醚反应生成C₁₂H₁₀O-OH 加合物, N₂条件下C₁₂H₁₀O-OH衰减的速率常数为(1.86±0.14)×10⁵ s^－1, 在有氧条件下, C₁₂H₁₀O-OH可转化为C₁₂H₁₀O-OHO₂, 衰减的速率常数为(6.6±0.4)×10⁶ s^－1. N₂条件下最终产物为苯酚、2-羟基二苯醚、4-羟基二苯醚、4-硝基二苯醚.     

Dimerization of dioxovanadium(v) ions in the presence of cyclohexenyl hydroperoxide

The structure and properties of the intermediate that is formed in the reaction of VO(DMSO)₅(ClO₄)₂ with cyclohexenyl hydroperoxide and characterized by the band at λ_max=402 nm in the electronic absorption spectra of its solution were considered using quantum-chemical concepts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1443–1446, August, 1997.     

Mechanistic studies of the photorearrangement of o-nitrobenzyl esters

α-Methyl-o-nitrobenzyl isobutyrate and copolymers containing α-methyl-o-nitrobenzyl acrylate were irradiated in dilute solution with 20 ns flashes of 347 nm light or with 60 ps flashes of 355 nm light. The formation of the absorption spectrum of a nitronic acid with τ = 5 ns was observed in each case. A transient absorption spectrum similar to that of the nitronic acid was formed with τ ⩽ 0.5 ns. This spectrum is assumed to belong either to the triplet biradical formed upon intramolecular triplet state hydrogen abstraction or to nitronic acid formed very rapidly by intramolecular singlet state hydrogen abstraction, the latter mechanism being operative in parallel with the triplet mechanism.In 60vol.%EtOH-40vol.%H₂O the nitronate anion was formed by dissociation of the nitronic acid with τ = 3 μs as indicated by a build-up of a new absorption band with λ_max = 420 nm and by an increase in electrical conductivity. The conversion into the end products (nitroso compound and carboxylic acid) occurred at a much faster rate from the nitronic acid than from the nitronate anion: τ = 80 μs (CH₂Cl₂), τ = 360 μs (60vol.%EtOH-40.vol.%H₂O, 10⁻⁴ M H₂SO₄) and τ = 10 ms (60vol.%EtOH-40vol.%H₂O, no H₂SO₄). Conversion of the nitronate anion into another transient was inferred from the partial decrease in the electrical conductivity (τ ≈ 15 μs).Irradiation of the copolymers gave the same results as for the low molecular weight model compound, indicating that there is no polymer effect with respect to the kinetics or the mechanism of the photorearrangement. This conclusion was substantiated by the quantum yields for acid formation (0.24 – 0.25) measured with both the model compound and the copolymers.     

Resolved single vibronic level fluorescence after two-photon excitation of benzene vapor: a direct confirmation of the inducing mode

Flourescence spectra have been observed from 1 and 5 torr of benzene after 504.2 nm excitation of the strongest two-photon band (linear polarization, ω₁ = ω₂) in the forbidden 260 nm ¹B_2u ← ¹A_1g absorption. The flourescence structure at 0.2 nm resolution is consistent with that expected from the fundamental ν′₁₄ in the excited state. This confirms directly the previous assignments of the dominant two-photon absorption progression as 1ⁿ_o14^L_o as well as the identity of the principal inducing mode, ν′₁₄ (b_2u). Vibrational relaxation from the level 14¹ appears similar to that observed from the one-photon levels.     

Investigation of the structure of 1,2-dihydro-3-(2-hydroxyphenyl)-4-nitropyrazol-5(3H)-one by spectroscopic and quantum-chemical methods

The structure of the previously synthesized 1,2-dihydro-3-(2-hydroxyphenyl)-4-nitropyrazol-5(3H)-one (I) was studied by ¹H and ¹³C NMR, IR, and electronic spectra. It was established that the NMR spectra of compound (I) do not contain signals for the H atom at position 4 and the C atoms of the carbonyl groups; in the crystalline state and in solutions the IR spectra do not contain v_c=o bands, while the electronic spectra do not contain absorption in the region of 250 nm. On the basis of the foregoing it is concluded that compound (I) exists in the OH form. The distribution of -electron density in the molecule of (I) and the nature of the bands in its electronic absorption spectrum were studied by quantum-chemical methods in the PPP approximation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1510–1516, November, 1990.     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

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.     

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     

Electrochemical synthesis of Co,Ni, and Zn complexes with 2-Pyrrole-[N-(o-hydroxyphenyl)methylimines]: The crystal structure of 2,2′-Bipyridine bis{2-[(2-pyrrole)methylimino]5-methylphenolato}nickel(II)

The electrochemical oxidation of anodic cobalt, nickel, and zinc in acetonitrile containing both 2-pyrrole-[N-(o-hydroxyphenyl)methylimines] (H₂L) and a bidentate ligand (1, 10-phenanthroline(phen) or 2,2′-bipyridine(bipy)) yielded compounds of general formula M(HL)₂ · phen and M(HL)₂ · bipy (M = Co, Ni, Zn). The crystal structure of 2,2′-bipyridine bis{2-[(2-pyrrole)methylimino]5-methylphenolato}nickel(II) was determined by X-ray diffraction. This compound crystallizes in the orthorhombic space group Pccn with a = 19.430(2), b = 28.488(2), c = 17.567(1) Å. The nickel atom has a distorted octahedral geometry, and the pyrrole nitrogen is not coordinated. The IR, ¹H-NMR and UV-visible spectra of the complexes are discussed and related to the structure.     

Matrix effects on the fast atom bombardment mass spectra of palladium complexes

In an attempt to identify and characterize the intermediates involved in multi-step palladium catalyzed coupling reactions, under fast atom bombardment (FAB) conditions, the selection of a matrix to enhance ion formation without degrading the palladium complex is critical. In general, it is observed that the analysis of tetrakis(triphenylphosphine)palladiurn(0) using glycerol, m-nitrobenzyl alcohol or o-nitrophenyl octyl ether as the FAB matrix compound produces several ions which correspond to complexes of the type Pd_xL_yO_z⁺ (L = PPh₃; x = 1-4; y = 1-4; z = 0-2), in addition to clusters containing one or more matrix molecules. FAB mass spectra generated using triethanolamine- or tetramethylene sulfone (sulfolane) are observed to contain ions related to the palladium(0) complex with little or no interference from ions related to the oxidation or reduction processes.