Luminescence from thermally oxidized model amides in relation to nylon 66 degradation

Fluorescence and phosphorescence are observed following the mild thermal oxidation of two model compounds for nylon 66. Both emissions are remarkably similar in structure and in wavelength location to the corresponding emissions normally observed from the commercial polymer. Although the fluorescence could not be characterized, the phosphorescence exhibits several features which are clearly consistent with that of a nπ* carbonyl emission. The role of carbonyl groups in the thermal and photochemical oxidation of nylon 66 is discussed.     

Effect of photochemical oxidation on polypropylene phosphorescence

Phosphorescence from polyolefins was studied from the aspects of excitation and emission wavelength and lifetime. Effects of photochemical oxidation on polypropylene phosphorescence are discussed in contrast to the effects of thermal oxidation.     

Mechanistic studies on the photo-oxidation of commercial poly(butadiene)

Products from both the thermal and photo-oxidation of poly-butadiene have been studied using various analytical techniques such as infra-red and ultra-violet spectroscopy, gas-liquid chromatography and phosphorescence emission and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photo-oxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α, β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.     

Analysis of the fluorescent and phosphorescent species in nylon-6,6 in relation to aldol condensation products of cyclopentanone

Fluorescence analysis of nylon-6,6 polymer indicates the presence of a number of chromophoric species. One of the main species has excitation maximum at 290 nm with a corresponding emission maximum at 326 nm and is extractable from the polymer by 2-propanol; another has an excitation maximum at 340 nm and corresponding emission maximum at 390 and 420 nm and is virtually non-extractable. The latter, as established by other workers, is associated with the presence of α-ketoimide structures formed by thermal oxidation of the molecular backbone of the polymer. The former, after isolation from cyclic nylon monomer using silica TLC, is shown to possess two excitation maxima at 228 and 284 nm and regenerates on exposure of the extracted polymer to pure oxygen and is attributed to a slow ambient oxidation process and not absorption of naphthalene from the “urban atmosphere”. This is confirmed by hydroperoxide analysis of the polymer before and after regeneration. Despite large scale extraction procedures (∼ 2 kg polymer), only trace amounts of the fluorescent species could be isolated after TLC analysis. However, using GC-mass spectrometry interfaced to a computer library (courtesy of ICI Organics Division plc, Manchester) the presence of cyclic enone dimer and dienone trimer of cyclopentanone amongst other products was confirmed in the 2-propanol extract. The phosphorescence emission from the polymer is shown to correspond to a complex mixture of these products and is little affected by 2-propanol extraction. Both the fluorescent and phosphorescent species in nylon-6,6 polymer are shown to originate from aldol condensation products of cyclopentanone. This is confirmed through a detailed luminescence/GC-mass spectrometry analysis of the products of the latter process. Feasible mechanisms, based on earlier nylon oxidation studies, are discussed.     

DNA cleavage by UVA irradiation of NADH with dioxygen via radical chain processes

Efficient DNA cleaving-activity is observed by UVA irradiation of an O(2)-saturated aqueous solution of NADH (beta-nicotinamide adenine dinucleotide, reduced form). No DNA cleavage has been observed without NADH under otherwise the same experimental conditions. In the presence of NADH, energy transfer from the triplet excited state of NADH ((3)NADH*) to O(2) occurs to produce singlet oxygen ((1)O(2)) that is detected by the phosphorescence emission at 1270 nm. No quenching of (1)O(2) by NADH was observed as indicated by no change in the intensity of phosphorescence emission of (1)O(2) at 1270 nm in the presence of various concentrations of NADH. In addition to the energy transfer, photoinduced electron transfer from (3)NADH* to O(2) occurs to produce NADH(*+) and O(2)(*-), both of which was observed by ESR. The quantum yield of the photochemical oxidation of NADH with O(2) increases linearly with increasing concentration of NADH but decreases with increasing the light intensity absorbed by NADH. Such unusual dependence of the quantum yield on concentration of NADH and the light intensity absorbed by NADH indicates that the photochemical oxidation of NADH with O(2) proceeds via radical chain processes. The O(2)(*-) produced in the photoinduced electron transfer is in the protonation equilibrium with HO(2)(*), which acts as a chain carrier for the radical chain oxidation of NADH with O(2) to produce NAD(+) and H(2)O(2), leading to the DNA cleavage.     

Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene)

The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established.     

The Emission in the Acetone Photochemical System

The emission in the acetone photochemical system has been measured as a function of irradiating time and pressure. The emission yield generally increases with increase in irradiating time at both 3130 and 2654A. The increase of emission yields is due to the sensitized phosphorescence of the product biacetyl. The higher emission yield and lower biacetyl quantum yields at 3130A than that at 2654A support for that most of the excited acetone molecules are in the triplet state at 3130A.     

Luminescence and Stability of 1,4,5-Triaryl-1,2,3-Triazoles

The fluorescence, phosphorescence, and photochemical properties of di- and triaryl-substituted-1,2,3-triazoles are reported in this work. The ease of synthesis of regioisomers of substituted triazoles enables a systematic study on the correlation between regiochemistry and excited state properties, which include the solvent dependence of fluorescence, energy gap between singlet and triplet emitters, and propensity to photon-triggered transformations. The triazoles that carry electron (e)-donor and e-acceptor aryl substituents show high fluorescence quantum yields in weakly polar solvents and exhibit solvent-dependent fluorescence. The luminescence properties of these compounds in glass matrices at 77 K are characterized. The thermal and photo-stability, two parameters that are crucial to their potential utilities in optical devices, of these compounds are determined. The position of the e-donor substituent has a significant impact on the fluorescence emission energy and solvent sensitivity, singlet-triplet energy gap, and photochemical reactivity and stability. The experimental observations on the structural correlation with the photophysical and photochemical properties are explained by quantum chemical calculations. This study provides a rationale on the placement of substituent on a donor-acceptor type fluorophore to maneuver a range of photo-related properties.     

New Optical Sensors for Oxygen Based on Phosphorescent Cationic Water-Soluble Pd(II), Pt(II), and Rh(III) Porphyrins

A new material is proposed for optical sensors for molecular oxygen; the material is obtained by the introduction of Pd(II), Pt(II), and Rh(II) complexes of cationic water-soluble porphyrins into an MF-4SK ion-exchange polymer membrane. The phosphorescence of immobilized metal porphyrins is efficiently quenched by molecular oxygen both in the gas phase and in aqueous solutions. The Stern–Volmer relationships for phosphorescence quenching are linear over the entire range of oxygen concentrations. The new material exhibits good response times and high photochemical stability.     

ON THE ROOM TEMPERATURE PHOSPHORESCENCE OF WOOL KERATIN

Abstract—A study has been made of the room-temperature phosphorescence behaviour of wool keratin and its major constituent proteins. The 290 nm induced phosphorescence of wool, previously thought to decay by second-order kinetics, is shown to consist of two separate components which decay exponentially with lifetimes of 0.18 × 0.03 and 1.45 × 0.25 s. Selective oxidation of the tryptophyl residues eliminates the long-lived phosphorescence, but has no effect on the short-lived component. The latter is variable in its intensity, and depends upon the history of the fibre. The origins of the different emissions are discussed, and the possible involvement of the phosphorescent species in the photochemical reactions leading to discoloration of the fibre are considered.     

Phosphorescence from epoxy resins: Evidence for an associated ground-state aggregate and triplet excimer

The phosphorescence properties of an epoxy resin film are examined and compared with the corresponding properties of the uncured resin in solution. At relatively high concentrations of resin the monomeric Bisphenol A emission at 405 nm is replaced by a longer wavelength emission at 460 nm, together with a corresponding shift in the excitation spectrum. The polymer phosphorescence is associated with the presence of an associated ground-state aggregate and triplet excimer.     

Designing systems for a multiple use of light signals.

The photochemical and photophysical behavior of two dendrimers consisting of a benzophenone core and branches that contain dimethoxybenzene units has been investigated. Such dendrimers can undergo a variety of photochemical and photophysical processes, namely: 1) quenching of the fluorescence and phosphorescence of the dimethoxybenzene units by energy transfer to the benzophenone core (antenna effect), 2) direct and sensitized phosphorescence (and delayed fluorescence) of the benzophenone core, 3) hydrogen abstraction by the triplet excited state of the benzophenone core from solvent molecules, 4) intramolecular hydrogen abstraction by the triplet excited state of the benzophenone core from the dendrimer branches, 5) quenching of the phosphorescence and hydrogen abstraction reaction of the benzophenone core by energy transfer to terbium ions and dioxygen; 6) conversion of the UV light absorbed by the dendrimer branches into visible (Tb3+) or near infrared (O2) emission via the sequence of processes 1) and 5). The results obtained emphasize the great potential of suitably designed dendrimers for a multiple use of light signals.     

Problems in the Study of Electro-Lum inescence Devices Based on Phosphorescent Dyes

本文从光物理和光化学的角度出发对磷光电致发光器件中的一些基本过程和问题, 如发光层材料的选择和激发, 主体化合物分子间的能量迁移, 主客体分子间的能量转移以及磷光的发射等进行了扼要的讨论, 并指出了在设计和制备这类新型的发光器件中应注意的一些问题。     

Synthesis and properties of a new photostable polymer: Perylene-3,4,9,10-tetracarboxylic acid-bis-(N,N′-dodecylpolyimide)

The synthesis of perylene-3,4,9,10-tetracarboxylic acid-bis(N,N′-dodecyl-polyimide) (poly PTDI) and polyamic acid has been achieved from perylene dianhydride and dodecylamine. It was found that this new polyimide has very high thermal photostability. Poly PTDI decomposes at 475°C and shows weak fluorescence compared with the monomer PTDI possibly due to aggregration in the polymer. Its solubility in some of the common organic solvents, acetonitrile, dimethyl formamide, etc., makes spectroscopic and photochemical studies and applications possible in the liquid phase. The emission characteristics are similar to mono PTDI. Poly PTDI, a luminescent electron acceptor polymer, is a new reliable probe for a photosensitizer at energy transfer and election transfer photochemical reactions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2137–2142, 1997     

Temperature dependence of tryptophan phosphorescence in proteins

The phosphorescence yield and decay kinetics of tryptophan (Trp) in apoazurin from Pseudomonas aeruginosa, subtilisin Carlsberg, Staphylococcal nuclease and liver alcohol dehydrogenase were determined as a function of temperature from 150 K (glassy matrix) to 300 K (fluid solution). The constancy of the lifetime-normalized phosphorescence yield with apoazurin and with Trp-314 in alcohol dehydrogenase establishes that the intersystem crossing quantum yield is practically unaffected across the temperature range. Consequently, any decrease in phosphorescence intensity not accounted for by lifetime-shortening is a signal either of the selective quenching of specific Trp residues in the same macromolecule or that the protein sample is heterogeneous in its emission properties. From an analysis of the thermal profile it is concluded that subtilisin Carlsberg and S. nuclease, as opposed to apoazurin, are not phosphorescent at ambient temperature, their residual emission probably arising from protein impurities. Criteria for distinguishing conformer emission from a contribution by protein impurities are discussed.     

An oxyluminescence investigation of the auto-oxidation of nylon 66

The kinetics of the thermal oxidation of stabilised and unstabilised nylon 66 fibres and films have been studied by photon counting oxyluminescence methods from 50°C to 150°C. The activation energies for initiation (E₁), propagation (E₃) and termination (E₅) over this temperature range are: E₁ = 16 kcal mol^?1, E₃ = 17·5 kcal mol^?1 and E₅ ≈ 12 kcal mol^?1. The extent of orientation of the polymer does not change the nature of the oxyluminescence curve or E₃ and E₅ above 110°C.Significant losses of critical mechanical properties of the fibres occur in the induction period at 100°C and non-stationary kinetics are described to enable this region to be studied by oxyluminescence. The oxidation rate in the induction period and the limiting rate region in air is one-third the rate in oxygen at atmospheric pressure. Non-stationary methods show that alkyl radical reactions are competitive with alkyl peroxy radical formation in air over the temperature range 100°C to 140°C. This affects the course of the oxidation reaction and the stabiliser efficiency and explains the observation of unsaturated oxidation products by phosphorescence spectroscopy.     

Photo-stabilising action of metal chelates in polypropylene—Part I: Excited state quenching versus UV antioxidant action under polychromatic irradiation

The photo-stabilising action of three metal chelates—nickel (II) 2,2′ thiobis (4-tert-octylphenylato) n-butylamine and the nickel and calcium derivatives of bis (ethyl-3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate, in polypropylene—is examined using normal and second order derivative ultraviolet, infra-red and phosphorescence spectroscopic techniques and hydroperoxide analysis. Whilst all three stabilisers quenched the phosphorescence emission of a powerful photo-sensitiser, benzophenone, there was no protective action during photo-sensitised oxidation of the polymer. In the case of anthraquinone, there was no quenching and no protection. Processing history plays a dominant rôle in controlling the photo-stabilising performance of the chelates. Each stabiliser operates differently, being dependent on its relative stability during processing and photo-oxidation and on the formation and destruction of polymeric and antioxidant hydroperoxides during processing. Metal chelates operate by inhibiting polymer hydroperoxide formation during processing and acting as ultraviolet stable chain terminators or by giving products during the early stages of photo-oxidation which are themselves effective stabilisers.     

Amorphous Ionic Polymers with Color‐Tunable Ultralong Organic Phosphorescence

Amorphous purely organic phosphorescence materials with long‐lived and color‐tunable emission are rare. Herein, we report a concise chemical ionization strategy to endow conventional poly(4‐vinylpyridine) (PVP) derivatives with ultralong organic phosphorescence (UOP) under ambient conditions. After the ionization of 1,4‐butanesultone, the resulting PVP‐S phosphor showed a UOP lifetime of 578.36 ms, which is 525 times longer than that of PVP polymer itself. Remarkably, multicolor UOP emission ranging from blue to red was observed with variation of the excitation wavelength, which has rarely been reported for organic luminescent materials. This finding not only provides a guideline for developing amorphous polymers with UOP properties, but also extends the scope of room‐temperature phosphorescence (RTP) materials for practical applications in photoelectric fields.     

A platinum acetylide polymer with sterically demanding substituents: effect of aggregation on the triplet excited state

The effect of interchain interaction on the triplet excited state is explored in two Pt-acetylide polymers of the type [-trans-Pt(PBu(3))(2)-C triple bond C-Ar-C triple bond C-](n), where Ar is either 1,4-phenylene or is based on the pentiptycene unit (polymers 2 and 3, respectively). To explore the effect of interchain interaction in Pt-acetylide materials, the optical properties of parent polymer 2 are compared with those of polymer 3 in which interchain interaction is precluded by the sterically bulky pentiptycene moiety. Insight into the effect of the pentiptycene unit on packing in the solid state comes from the X-ray structure of monomer 1b, Ph-C triple bond C-[trans-Pt(PBu(3))(2)]-C triple bond C-Ar-C triple bond C-[trans-Pt(PBu(3))(2)]-C triple bond C-Ph. Spectroscopic studies indicate that weak phosphorescence emission from an interchain aggregate is observed from parent polymer 2, both in solution and in the solid state. By contrast, the photophysics of 3 is dominated by the intrachain triplet exciton. Interestingly, the phosphorescence emission of polymer 3 in the solid state is nearly superimposable with that of a single crystal of monomer 1b, suggesting that the solid polymer experiences an environment that is similar to that of the monomer in the crystal.     

无色孔雀绿光氧化反应的途径

前一篇文章已说明,无色孔雀绿(LMG)经光氧化生成孔雀绿(MG⁺)染料是一个复杂的光化学过程。萘加入反应溶液猝灭了LMG的激发态,但却使反应速率升高。对这一实验结果我们曾推断为:可能是由于萘与LMG之间发生了电子转移作用。本文将对这一推断作进一步实验论证,并将说明在没有电子受体参加时,LMG的光氧化主要通过其激发三线态途径进行。已得到的实验结果证明,我们的上述推断是正确的,现予以报道。