Absorption Spectra Of Poly Research Articles

A new method for the quantitative analysis of the ultra-violet/visible spectrum of poly(butadienyl-lithium) anions when complexed with 1,2-dipiperidinoethane

The ultra-violet/visible absorption spectrum of poly(butadienyl-lithium) anions in living anionic polymerization reactions changes significantly in the presence of the complexing agent 1,2-dipiperidinoethane (DIPIP). In the absence of complexing agent the poly(butadienyl-lithium) anion has an absorption maximum at 275 nm in cyclohexane, but on adding DIPIP two broad unresolved absorption maxima are observed in the range 250 to 400 nm, and the extinction coefficients for these peaks vary with the molar ratio of DIPIP to the living chain ends. A method has been developed for the determination of the concentration of the complexed living polyanions in cyclohexane by monitoring the absorbances at two different wavelengths (275 and 325 nm), which provides a useful means of obtaining a quantitative understanding of the living polymerization process in the presence of the complexing agent that was not possible before. The living-end concentrations obtained using the method proposed here have been found to be in good agreement with values obtained by measurement of the number-average molecular weights of the final products. Using this method, it has also been demonstrated that, in addition to forming a complex, DIPIP reacts slowly with the poly(butadienyl-lithium) anions.

A Novel Unsymmetrical Poly(1-N-Carbazolyl) Diacetylene for Non Linear Optics

ABSTRACTPhotoinduced absorption spectra of poly(1-N-carbazolyl-penta-1,3.diyne-5-acetoxy) show absorption peaks which depend on the sample preparation and on the temperature. The low temperature spectra show two well resolved absorptions centered at ∼0.5 and ∼1.2 eV respectively. In view of other experimental results on these systems, we have interpreted our data as evidence of charged bipolarons stabilized by interchain interactions.

Temperature Depenndence of the Doping Effect of Poly(3-alkylthiophene) and Polaronic State

The absorption spectrum of poly(3-alkylthiophene) such as poly(3-docosylthiophene) changes at the solid-liquid phase transition. This phenomenon can be interpreted in terms of the change of the effective conjugation length due to the existence of some twisted bonds between neighbouring thiophene rings on the polymer main chain in the liquid state. From measurements of the cyclic voltammogram in solid and liquid phases, the top of the valence band is confirmed to be located at a higher energy in the liquid state. Formation of polaronic states, even in the liquid state, has been clarified from the drastic change of absorption spectrum upon doping. A simple energy band scheme of poly(3-alkylthiophene) in the solid and liquid states is indicated.

Dynamical calculations on the photoisomerization of small polyenes in a nonadiabatic formalism

The dynamics of the cis–trans isomerization in 10° monopyramidalized ethylene, butadiene, and hexatriene has been studied in a nonadiabatic treatment including explicitly the twisting motion. The electronic energy curves, (transition) dipole moments, and nonadiabatic couplings have been obtained from ab initio CI calculations. An initially (Franck–Condon) excited wave function is constructed from the final vibrational eigenfunctions and energies. The appearance of the calculated prepared state is discussed in relation to the increasing line broadening vs decreasing chain length of the primary vibrational bands in the 1 1B+u absorption spectra of polyenes. It is found that this feature can be explained from the increasing tendency of shorter polyenes to be nonplanar in the excited state. The time evolution of the molecules is monitored by calculating the radiationless decay, the dipole moment, and the contributions of the electronic states to the total wave function. The role of the nonabsorbing 2 1A−g state is discussed. It is demonstrated that the dynamics of the cis–trans isomerization are directly correlated to the shape of the potential energy curve of the absorbing excited state. Ethylene is found to rotate once about the double bond in 0.075 ps and butadiene in 0.2 ps, whereas hexatriene is excited to an almost stationary wave function. Because of the limitations of the present model, the molecules do not show any substantial (‘‘sudden’’) polarization upon inclusion of the nonadiabatic coupling. For the same reason, the contribution of the electronic ground state to the total wave function is small.

Calculation of frequencies and intensities in the IR absorption spectrum of poly(tetrafluoroethylene)

Calculation of frequencies and intensities in the IR absorption spectrum of poly(tetrafluoroethylene)

Preparation and electrical properties of poly(3‐thienylacetylene)

Abstract3‐Thienylacetylene (1) was prepared by reaction of 3‐(2,2‐dichloro‐1‐fluorovinyl)thiophene with butyllithium in a 1 : 2 mole ratio, and subsequent hydrolysis. Polymerization of 1 with WCl6 and tetraphenyltin gave poly(1), poly[1‐(3‐thienyl)vinylene], which contained a small amount of benzene‐insoluble product. On heating poly(1) no weight loss was observed up to 240°C. At 500°C the weight loss was 18%. In differential scanning calorimetry, an exothermic peak appeared at 245°C. A pressed pellet, doped with iodine, exhibits conductivity of about 10−3 S/cm. The absorption spectrum of poly(1) shows a shoulder at 225 nm, a maximum absorption at 360 nm and tailing up to about 660 nm. In a solution of poly(1) and I2, a new absorption appeared in the near‐infrared region, but failed to develop enough to suggest high conductivity of poly(1) doped with iodine. The electrochemical doping of poly(1) and electrochemical polymerization of 1 gave no conducting products.

Absorption Spectra of Poly(L-vinylpyrene) in the Excited and Ionic States

Absorption Spectra of Poly(L-vinylpyrene) in the Excited and Ionic States

Laser photochemistry of polymers

Absorption spectra of poly(N-vinyl-carbazole) and related polymers in the excited singlet, triplet, cationic, and anionic states were measured by nanosecond and picosecond laser photolysis methods and compared with those of model bichromophoric compounds. Absorption spectral shape of the excited singlet and cationic states is a function of polymer structure and sensitive to relative geometrical structure of two carbazolyl groups. The excited singlet species in poly(N-vinylcarbazole) are the sandwich excimer, the excited dimer with the partial overlap structure between two chromophores, and the so-called second excimer. The formation process of the sandwich excimer consists of an instantaneous rise and a slow one with a time-constant of a few hundred ps. The absorption spectrum of poly(N-vinylcarbazole) cation can be reproduced by a superposition of absorption bands of the sandwich dimer cation, the dimer cation with the partial overlap, and the dimer cation with the open form. On the other hand, absorption spectra of the triplet and anionic polymers are similar to those of the corresponding monomer model compound, showing a very weak interchromophoric interaction. All these results indicate that electronic excitation and charge in these polymers are not delocalized over several chromophores but trapped in some monomer and dimer sites. Dynamic behavior such as conformational change, intersystem crossing, photochemical formation yield of ion radicals, and their decay kinetics was also studied in detail.

Circular dichroism of collagen, gelatin, and poly(proline) II in the vacuum ultraviolet.

AbstractCircular dichroism spectra for acid‐soluble calfskin collagen, gelatin, and poly(proline) II in solution have been extended into the vacuum ultraviolet region. The extended spectrum of gelatin reveals that the circular dichroism of this unordered polymer is more closely related to the spectrum of charged polypeptides than might be evident from near ultraviolet work. A short‐wavelength band is found at about 172 nm, which corresponds in position, magnitude, and sign to a band recorded earlier for poly(L‐glutamic acid) at pH 8.0. This band is observed in a helical structure for the first time in the vacuum ultraviolet circular dichroism and absorption spectra of poly(proline) II. Both circular dichroism and absorption spectra point to the assignement of this band as the nσ*. Neither the nσ* nor the expected positive lobe of the ππ* helix band is observed in the extended circular dichroism spectrum of collagen. We postulate that these two bands cancel here in analogy to the case of α‐helical poly(L‐glutamic acid).

Physical studies on synthetic DANs containing 5-methylcytosine

In synthetic DNAs in which cytosine or 5-methylcytosine is base-paired with guanine or hypoxanthine, the physical properties depend both on base composition and base sequence. The absorption spectra of poly(dI) · poly(m 5dC) and poly(dI-m 5dC) · poly(dI-m 5dC) closely resemble the spectra of an equimolar mixture of nucleotides; the maxima near 250 nm corresponds to dIMP absorption and the shoulder at 278 nm corresponds to 5-methyldeoxyCMP absorption. In contrast, when dIMP is replaced by dGMP, the maxima remain near 250 nm, but there is no shoulder; the pyrimidine absorption appears to be blue-shifted by approx. 28 nm. The fluorescence of 5-methyldeoxyCMP is unperturbed when incorporated into randomcoil poly(m 5dC) and is blue-shifted by approx. 8 nm when incorporated into poly(dI-m 5dC) · poly(dI-m 5dC). Incorporation of 5-methyldeoxyCMP into poly(dG-m 5dC) · poly(dG-m 5dC) reduces the fluorescence yield several-fold and blue-shifts the emission by approx. 50 nm. Methylation of pyrimidines raises the melting temperature of both poly(dR-dY) · poly(dR-dY) and Poly(dR) · poly(dY) and reverses the order of melting: methylation (and also bromination) gives the homopolymer pair a higher melting temperature than the alternating copolymer. Methylation also invariably reduces the buoyant density of the synthetic DNAs in neutral and alkaline CsCl, but the decrement is not constant. Methylation of poly(dI-dC) also recudes its buoyant density in neutral and alkaline Cs 2SO 4. Methylation of poly(dG-dC) increases its buoyant density in neutral Cs 2SO 4 and reduces it in alkaline Cs 2SO 4.

The synthesis of the alternating copolymer poly(r(A-s4U)) by RNA polymerase of Escherichia coli.

The transcription of poly [d(A‐T)] by RNA polymerase from Escherichia coli in the presence of ATP and 4‐thiouridine triphosphate (s4UTP) lead to the synthesis of poly[r(A‐s4U)]. The investigation of the polymerisation kinetics furnished the kinetic parameter Km (ATP‐s4UTP) = 0.33 mM and Vmax (ATP‐s4UTP) = 204 nmoles AMP × mg enzyme−1× min−1.The structure of poly[r(A‐s4U)] was proved by nearest neighbour analysis and calculation of the AMP/s4UMP ratio from the absorption spectrum of poly[r(A‐s4U)]. As shown by sedimentation velocity analysis poly[r(A‐s4U)] exhibited a mean s20, w value of 12 S. Enzymatic hydrolysis and thermal denaturation of poly[r(A‐s4U)] revealed the existence of a large hyperchromicity in the absorption spectrum. The absorption‐temperature profile of poly [r(A‐s4U)] measured at 0.08 M Na+ showe a sharp cooperative transition with a Tm of 52°C.

Absorption spectrum of gamma-irradiated poly(methylmethacrylate) within the range 245 to 450mμ

The absorption spectrum of poly(methylmethacrylate) irradiated with γ-rays at room and liquid nitrogen temperatures has been studied within the range 245 to 450 mμ. The materials used varied considerably in nature and concentration of initiator and chain-transfer agent additives. Most of the samples irradiated at liquid nitrogen temperature showed peak absorption wavelengths very close to those noted after room-temperature irradiation; a minority group showed shorter peak wavelengths, which shifted to the room-temperature values when subsequently warmed to room temperature. A marked dependence of spectral behaviour on both initiator and chain-transfer agent content was noted, indicating that most of the absorbing species originate in the additives; on the other hand, an absorption peak around 252 mμ was found in several samples independent of their additive content, and also independent of the temperature of irradiation. As a strong absorption peaking close to this wavelength was observed in radiation polymerized poly(methylmethacrylate), it is postulated that the species giving rise to this particular absorption is formed on methylmethacrylate monomer residue in the polymer. Evidence is presented to show that the absorbing species are not radicals. It is possible that they are ionic in nature, probably cations. It is postulated that the absorbing species formed on the monomer residue is a carbanion C̈HCHCH which, with appropriate electron pairing, would not give rise to an e.s.r. signal. Of the materials polymerized with the help of additives, those containing fairly large concentrations of mercaptan compounds as chain-transfer agents showed a slowly decaying absorption peaking around 252 mμ at liquid nitrogen temperature and 255 mμ at room temperature; the species giving rise to this absorption is to be distinguished from that formed on monomer residue. Materials containing benzoyl peroxide initiator showed peak absorption values around 280 and 290 mμ, independent of temperature.

The Free-Electron Model, "Overtone" Bands, and Vibrational Structure in Absorption Spectra of Polyenes and Polyenynes.

The Free-Electron Model, "Overtone" Bands, and Vibrational Structure in Absorption Spectra of Polyenes and Polyenynes.

Empirical Relationships of the Minor Bands in the Absorption Spectra of Polyenes.

Empirical Relationships of the Minor Bands in the Absorption Spectra of Polyenes.