Synthesis of alkyl and N-alkyl-substituted polyanilines: A study on their spectral properties and thermal stability

Polyaniline (PANI), N-methyl- and N-ethyl-PANI, 2- and 3-ethyl-PANI as well as 2,6-dimethyl- and 3,5-dimethyl-PANI have been synthesized using ammonium persulfate as catalyst. These polymers have been studied in the undoped and doped state by FT-IR and electronic spectroscopy in the range from the UV-VIS to the NIR portion of the spectrum. As doping agent camphorsulfonic acid was used. The chemical structures of the N-methyl- and N-ethyl-PANI have been found to contain quinoneimine units along the polymer chain. In the doped state the N-alkyl-PANIs show the polaronic band transition in the NIR part of the spectrum, at longer wavelength than doped unsubstituted PANI. A similar but less pronounced phenomenon is observed in the case of ethyl-substituted phenyl rings of PANI. Dimethyl-substitution at the phenyl ring of PANI hinders the formation of high molecular weight polymer. Only oligomers are formed.The thermal stability of unsubstituted PANI in the undoped state is very high and N-alkyl substitution and phenyl ring substitution lowers the thermal stability of PANI. Doped samples show a significantly worse thermal resistance in comparison to the corresponding undoped samples, this is due essentially to the volatility and the decomposition of the protonic acid used as dopant. Good general agreement has been found between the predicted thermal stability on the basis of increment groups calculations and the experimental results.The thermal decomposition of unsubstituted and undoped PANI has been followed by FT-IR spectroscopy.     

A study on the energy transfer and migration in the molecules of polymeric triplet sensitizers: (2) A study on delay fluorescence and polarization spectra

The triplet energy migration of polymers and copolymers of vinyl benzophenone (VBP) and vinyl naphthalene (VN) has been studied by measuring delayed fluorescence and polarization spectra in glassy dilute solution at 77 K. Strong delayed fluorescence of PVN proves the existence of triplet energy migration and T-T annihilation in the polymer chain. Efficient intersystem crossing of “BP” and efficient energy migration and transfer between chromophores along the polymer chain result in the absence of delayed fluorescence for copolymer P (VN-VBP) studied in this work. The order of benzophenone phosphorescence intensity: BP>Co (VBP-St)>PVBP indicates the T-T annihilation decreasing the phosphorescence of PVBP. Fluorescence and phosphorescence polarization data of polymers are smaller than that of their model compounds. It is evident that energy migration exists in the polymer chain.     

Intramolecular excimer formation in macromolecules—V. Head-to-head polystyrene,block copolymers of styrene and butadiene and regular condensation polymers of α-methylstyrene

Studies of the photophysical properties of head-to-head polystyrene, block copolymers poly(butadiene-b-styrene) and polystyrenes of various sequence length of styrene chromophore and regular copolymers of α-methylstyrene indicate that interactions between phenyl chromophores located distantly upon the macromolecule are not of major significance in determination of excimer formation in styrene polymers. It is concluded that intramolecular excimer formation in polystyrenes occurs primarily as a consequence of interactions between nearest neighbour chromophores in the polymer chain. The influence of polymer coil dimensions upon intramolecular excimer formation is demonstrated. The photophysical behaviour of poly(butadiene-b-styrene) block copolymers shows the importance of intramolecular energy migration in population of potential excimer sites.     

表面起伏光栅形成速率的影响规律 Ⅰ.偶氮生色团种类和官能度的影响

设计并合成了含有不同生色团以及不同官能度的环氧树脂基偶氮高分子 ,系统研究了偶氮生色团的种类和官能度对光栅形成速率的影响规律 .实验结果表明 ,偶氮苯对位是羧基的聚合物的光栅形成速率明显快于偶氮苯对位是硝基的聚合物 ,光栅形成速率随偶氮生色团官能度的增加而加快 .这两类聚合物都可以形成规整的可擦式表面起伏光栅     

Phosphorescence of carbonyl compounds produced by thermal and photo-oxidation of polybutadiene

Using phosphorescence analysis, the energy levels of the triplet states of some of the macrocarbonyl molecules formed in the photo-oxidation of commercial polybutadiene (48% trans, 42% cis and 10% vinyl) have been determined. The triplet energy levels of 26 additives were also determined so that predictions could be made regarding the probable efficiencies of these additives for quenching the excited states of the carbonyl species. These predictions have been substantiated by the observation of triplet-triplet quenching of a model α,β-unsaturated ketone in the solid state by one of the commercial u.v. stabilizers with a low-lying triplet energy level.     

POLYIMIDE/INORGANIC INTERPENETRATING POLYMER NETWORKS FOR STABLE SECOND-ORDER NONLINEAR OPTICS

Thermally stable NLO interpenetrating polymer networks (IPNs) based on an organosoluble polyimides functionalized with methacryloyl groups (PIB), and an alkoxysilane dye (ASD) have been developed. IPNs were formed through the free radical polymerization of methacryloyl group containing PIB, and sol-gel process of ASD. Optically clear samples exhibit large second-order optical nonlinearity (d₃₃ = 6.9-39.6 pm/V at 1064 nm) after poling and curing at 180°C for 2 hours. The temporal stability of the PIB/ASD IPN samples was much better than the inter-chain crosslinking polyimide/inorganic samples. The high rigidity of the polymer backbone and the interpenetrating structure of the polymer networks prevent the randomization of the aligned NLO chromophores     

Co-photolysis of poly(styrene) and poly(vinylacetophenone)—I. Vacuum photolysis

Films made from blends of poly(styrene) (PS) and poly(vinylacetophenone) (PVAP) (up to 12% mol PVAP) were exposed under high vacuum to long wave u.v. radiation (λ > 300nm). Spectral changes (phosphorescence, NMR and i.r. indicated that PVAP was photolysed: the nature of gaseous products (in order of abundance, methane, carbon monoxide, ethane and acetaldehyde) confirmed that PVAP was undergoing a Norrish Type I decomposition. There was also evidence of photoreduction, OH absorptions appearing in the i.r. The blended films undergo cross-linking but the insoluble material formed after about 10hr contains little carbonyl. The effects of PVPA concentration and molecular weight on the rate of product formation were also investigated. Experiments with poly(α-D-styrene) confirmed that methyl radicals were abstracting H atoms at the α-position in PS. The implications of such reactions in the initiation of photo-oxidation by polymeric ketonic species are discussed.     

Dendronized tricyanopyrroline‐based chromophores in nonlinear optical active host polymer

We synthesized new nonlinear optical (NLO) chromophores containing a 3,5‐bis(3,5‐bisbenzyloxy‐benzyloxy)‐benzoate dendron. Tricyanopyrroline (TCP)‐based chromophores were designed and prepared by virtue of its strong electron withdrawing property. A soluble polyimide containing 6‐({4‐[2‐(1‐allyl‐4‐cyano‐5‐dicyanomethylene‐2‐oxo‐2,5‐dihydro‐1H‐pyrrol‐3‐yl)‐vinyl]‐phenyl}‐butyl‐amino)‐hexanoyl group in the side chain was also prepared as an NLO active host polymer. A benzoate dendron was tethered at two different binding positions of the chromophore to yield two different guest molecules. Thin‐film composites of these dendronized chromophores dissolved in the NLO active polyimide host were employed to fabricate the electro‐optic (EO) samples. The EO properties of new NLO polyimides containing dendronized chromophores were compared with those of the sample with nondendronized plain chromophores. The effect of a bulky dendron on the EO properties was investigated using an in situ reflection technique. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5064–5076, 2008     

Time-dependent Phosphorescence Color of Carbon Dots in Binary Salt Matrices through Activations by Structural Confinement and Defects for Dynamic Information Encryption

The emergence of time-dependent phosphorescence color (TDPC) materials has taken information encryption to high-security levels. However, due to the only path of exciton transfer, it is almost impossible to obtain TDPC for chromophores with a single emission center. Theoretically, in inorganic-organic composites, the exciton transfer of organic chromophores depends on the inorganic structure. Here, we assign two structural effects to inorganic NaCl by metal (Mg²⁺ or Ca²⁺ or Ba²⁺) doping, which triggers the TDPC performance of carbon dots (CDs) with a single emission center. The resulting material is used for multi-level dynamic phosphorescence color 3D coding to achieve information encryption. The structural confinement activates the green phosphorescence of CDs; while the structural defect activates tunneling-related yellow phosphorescence. Such simply doped inorganic matrices can be synthesized using the periodic table of metal cations, endowing chromophores with tremendous control over TDPC properties. This demonstration extends the design view of dynamic luminescent materials.     

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.     

Phosphorescence sensitization via heavy-atom effects in d10 complexes

Heavy atom-induced phosphorescence of organic chromophores that originates from spin?Corbit coupling (SOC) is always accompanied by fluorescence quenching concomitant with a reduction of the triplet excited state lifetime. However, such changes are typically manifest by fluorescence quenching at room temperature and phosphorescence sensitization at cryogenic temperatures. Herein we overview our efforts over the past decade in which both internal and external heavy-atom effects (HAEs) can trigger room temperature phosphorescence (RTP) with dramatic shortening of the phosphorescence radiative lifetime by several orders of magnitude. Such spectral properties render new classes of phosphorescent materials for potential use in organic light-emitting diodes (OLEDs). The molecular systems described in this paper are organic fluorophores that are ??-complexed or ??-bonded to a multinuclear d¹⁰ transition metal center, the presence of which leads to phosphorescence sensitization because of the significant SOC in such materials.     

Phosphorescence of thermally oxidised poly(butadiene) and model enones: temperature dependence

The temperature dependence of phosphorescence of model enone compounds in poly (methyl methacrylate) matrix and glassy methylcyclohexane/isopentane solution and of enones formed from thermal oxidation of poly (butadiene) has been studied over the temperature range 77–220°K. The single discontinuity in the plot for the model enone-glassy solvent is due to the freezing of a (solvent perturbed) barrier to rotation in the enone, and an analogous transition is also observed in the model enone poly (methyl methacrylate) samples and in thermally oxidised poly (butadiene). In the polymer matrices, a second transition corresponding to the γ-transition in poly (methyl methacrylate) and the glass transition temperature T_g in poly (butadiene) are also revealed in the Arrhenius plots. The results demonstrate that care must be taken in ascribing such discontinuities solely to polymer properties since intrinsic properties of the luminescence probe itself may exhibit similar features.     

X-ray scattering study of molecular order in a liquid crystal-side group polysiloxane

The molecular structure of a polysiloxane with phenyl benzoate mesogenic side groups was investigated in an x-ray scattering study in the partially crystalline, smectic and nematic phase, and in the melt. In the crystalline phase polymer molecules have the form of straight ribbons with a double-comb-conformation. A bilayer structure is built up by regular stacking. Layers are the dominating structure element not only in the crystalline and smectic phase, but also in the nematic phase, and even in the isotropic melt. Layers are planar in the smectic phase and curved in the nematic phase, with an asymmetric distribution of the normal vectors about the director. In the isotropic melt there is evidence for the occurrence of clusters with layer-like short-range order.     

Thermally stable triaryl amino chromophores with high molecular hyperpolarizabilities

The synthesis of a series of high temperature triaryl amino chromophores with unprecedented hyperpolarizability values for potential EO applications is described. 4-(N,N-di-p-anisylamino)phenyl donors are for the first time bridged to powerful acceptors such as tricyanovinyldihydrofuran via vinyl thiophene linkages. The chromophores are readily soluble in common organic solvents, exhibit useful absorptions and high thermal decomposition temperatures (highest T_d=358 °C). Molecular hyperpolarizabilities (β) of the chromophores were measured by Hyper Rayleigh Scattering (HRS) at 1604 nm, which gave β values from 1000 to 20,000 × 10⁻³⁰ esu. The electrochemical behavior of the chromophores were studied by cyclic voltametry, and agree well with the intrinsic nonlinearities observed. These chromophores are of particular interest due to their large optical nonlinearities, transparency in the near IR, high thermal decomposition temperatures, and their potential to be incorporated into polymeric materials.     

Luminescence studies in polymers—X: Triplet energy migration in copolymers styrene-vinylbenzophenone. Decay-time and its relation to phosphorescence emission and excitation spectra

The decay of the phosphorescence of copolymers styrene-vinylbenzophenone excited with u.v. light of 365 nm either in glassy solution or as films at 77°K has been analysed. In glassy solution, the decay is exponential for a wide range of copolymer composition (τ = 5·10^?3 sec). The decay of films reveals the presence of a second type of trap with a longer life-time (τ = 2·10^?2 sec). The importance of these traps increases with the vinylbenzophenone content. The efficiency of triplet energy migration also increases with vinylbenzophenone content as a result of exchange interactions between benzophenone groups. The results are in agreement with Voltz's theory at moderate vinylbenzophenone content (<50 mole %).     

Thermal and photo-degradation of unstabilized ABS

Thermal- and photo-stabilities of unstabilized acrylonitrile-butadiene-styrene terpolymer, ABS, have been investigated by i.r. spectroscopy. Degradation of ABS samples is initiated by attack on the polybutadiene (PB) component; oxidation products containing hydroxyl and carbonyl groups are produced. The effect of prior thermal processing is to introduce into the polymer hydroperoxides arising from oxidative destruction of PB-unsaturation; these hydroperoxides act as catalysts during subsequent u.v. irradiation. The insolubility of degraded samples of ABS is associated with the formation of cross-linked structures and occurs mainly in the PB segment. It is concluded that the degradation characteristics of ABS are essentially those of the polybutadiene component.     

A relaxation study of poled nonlinear optical polymers by infrared reflection-absorption spectroscopy

The relaxation of poled nonlinear optical (NLO) chromophores in polymer films was characterized by infrared (i.r.) reflection-absorption spectroscopy. Both a guest-host system and a photocrosslinkable polymer system were investigated. Polymethylmethacrylate doped with either 2-methyl-4-nitroaniline or 4(4′-nitrophenylazo)aniline was studied. The photocrosslinkable polymer system, polyvinylcinnamate doped with 3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenyl azo]nitrobenzene was also investigated. Doped NLO active molecules were aligned using the corona poling technique. i.r. spectra as a function of time were used to monitor the relaxation behavior of the oriented dyes after poling. Relaxation of NLO molecules was followed at various characteristic vibrational frequencies. The relaxation behavior of both systems were found to be consistent with those studied by the second harmonic generation technique.     

PHOTOREVERSION VON VIER GRUPPEN UV-INDUZIERTER MUTATIONEN ZUR GIFTRESISTENZ IM NICHTPHOTOREAKTIVIERBAREN E. COLI

Abstract— In the non-photoreaclivable bacterial strain E. coli B/phr^-/MC2 the photoreversion of four groups of u.v.-induced mutations were investigated. They lead to resistance to Chloramphenicol (2 mg/l; "C"), Penicillin (13 or 16 mg/l; "P13" and "P16") or Streptomycin (3 mg/l; "S"). The u.v.-dose curve is concave for the C-mutations (two to three hits), about linear for P13 and S, and they reach peaks and decrease at high u.v.-doses. Though no photoreactivation of killing (PR) is present there is photoreversion of all four types of mutations (PRM). At u.v.-doses below the peaks in average about 43 per cent mutations are photoreversible. At high u.v.-doses the curves with light-post treatment (L) cross the darkcurves (D). In the photoreactivable strain B/r (by the spontaneous mutation MC2 to Mitomycin-resistance strain B/phr^- was made about as u.v.-resistant as B/r is) the photoreversion of the mutation groups C, P13 and P16 (S was not investigated here) was much higher, in average about 77 per cent at low doses. It is assumed that the difference in PRM of about 34 per cent between both strains is due to a PRM-mechanism present in B/r but not in B/phr^-/MC2; this mechanism may be the photoreactivating enzyme that opens thymine-dimers. The PRM in B/phr-/MC2 must then be due to a second mechanism which is probably not the dimer opening enzyme. It may be the same mechanism as in the case of mutations of phage kappa which are induced by u.v. and reversed partially by light, both extra cellularly. The premutations giving this second type of PRM may perhaps be cytosine-hydrate in the DNA. Tn average about 23 per cent mutations of B/r are photostable. Since this ratio decreases with low u.v.-doses in the C-mutations and increases in P13 and in P16 probably two types of photostable premutations seem to exist.     

Poly[(2,2′,5′,2″-tetramethoxy-p-terphenyl-5,5″-ylene)propylene]: Synthesis and physical properties of a novel amorphous regularly segmented conjugated polymer

A new regularly segmented conjugated polymer with methoxy-substituted p-terphenylene units tethered by their meta positions along the polymer main chain was synthesised using the Suzuki cross-coupling reaction. The small size of the connector and lack of long lateral chains lead to a high density of rigid electrooptically active moieties in the structure. However, this molecular architecture produces a very soluble and amorphous polymer with relatively high T_g. The optical properties of samples with different degrees of polymerisation were investigated using UV-visible absorption, steady state and time-resolved photoluminescence emission spectroscopies. Their absorption and emission properties are rather insensible to Mn after reaching a modest DP, to the aggregation state, either solution or neat film, and to annealing. The contorted polymer chain forms a very stable morphology and substantially hinders interactions between chromophores, thus diminishing the formation of aggregated species that are commonly observed in other electrooptically active polymers.     

以N为耦合中心多枝分子的双光子上转换荧光

采用非线性透过率法研究了以N为耦合中心的多枝化合物N-[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2-]苯基}-1-乙烯基}苯基}-N,N-二苯胺(BPODPA), N,N-双[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2-]苯基}-1-乙烯基}苯基}-N-苯胺(BBPOPA)和N,N,N-三[4-{2-(3,5-二-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2]苯基}-1-乙烯基}苯基}胺(TBPOA)的双光子吸收性质, 测定了化合物的单光子荧光光谱和双光子上转换荧光光谱, 研究了多枝化对三苯胺分子双光子吸收和双光子激发荧光性质的影响.在800 nm波长的激光激发下,化合物BPODPA、BBPOPA和TBPOA在二氯甲烷溶液中发出很强的蓝绿色双光子上转换荧光, 荧光峰分别位于502、515 和518 nm. 这些多枝结构化合物的双光子吸收截面较大, 双光子吸收增强来源于多枝分子中扩展的π共轭体系和重复单元的协同效应.