Polydiacetylene Films Research Articles

Influence of disorder on the field-modulated spectra of polydiacetylene films.

Electroabsorption and electroreflectance spectra of disordered, optically isotropic polydiacetylene films (4-BCMU) have been measured with field perpendicular to the incident light. The modulated spectra are polarized reflecting the local anisotropy of \ensuremath{\pi}-conjugated polymers. Based on results on single crystals, the data are interpreted as quadratic Stark effect of excitonic transitions with the same values for polarizability and dipole moments as in single crystals, accounting only for inhomogeneous broadening and random orientation of polymer segments. Line-shape analysis reveals a large additional contribution proportional to the second derivative of the absorption spectrum. This part, absent in single crystals, is interpreted as a linear Stark effect due to permanent dipole moments arising from disorder-induced asymmetry of polymer segments. Isotropic distribution of the disorder-related dipoles leads to a quadratic dependence of the signal on field strength, different from the quadratic Stark effect only by the spectral line shape.

Bulk Self-Assembled Films for Photonics

ABSTRACTRecently we have reported, significant second harmonic generation from spin coated and bulk films of a soluble polydiacetylene (PDA), namely poly{8-[[[butoxy carbonyl] methyl]urethanyl]-1-(5-pyrimidyl)-octa-l,3,-diyne}} (BPOD) without recourse to poling. Poly(BPOD) is an asymmetrically substituted PDA in which a polarizable heteroaromatic pyrimidyl group is attached as one of the side groups. In addition to reviewing the earlier results, we report a series of new soluble PDAs of the same class with further functionalization, elaborating on the already defined design principle.A second class of polymers with azo dye based NLO chromophores incorporated into the structure has been processed optically to fabricate holographic elements. Trans-cis-trans isomerization driven reorientation and macromolecular motion leads to the formation of surface relief gratings upon exposure to an interference pattern. Fabrication of optical elements based on these polymers will be elaborated.

Photodeposition of Thin Polydiacetylene Films from Solution That Exhibit Large Third-Order Optical Nonlinearities

One promising class of organic compounds for applications in the field of nonlinear optics (NLO) are polydiacetylenes, which are of interest because they are highly conjugated polymers capable of exhibiting very large optical nonlinearities with fast response times. During the course of crystal growth studies in anticipation of a space experiment, we discovered a novel, simple method for the formation of polydiacetylene thin films by photodeposition from monomer solutions onto quartz or glass substrates. Characterization of these PDAMNA films is not trivial; they are not soluble in common organic solvents, which makes the standard solution-based methods of polymer analysis useless.

RECENT DEVELOPMENT IN POLYDIACETYLENE SYNTHESIS: UNCONVENTIONAL POLYDIACETYLENES FOR NLO APPLICATIONS

Unconventional methods to obtain thin films of polydiacetylenes are described. These methods include preparation of films of polydiacetylene containing polymers, the preparation of polydiacetylene microcrystals dispersed in common polymers and the polymerization of diacetylenes in the molten state. It was shown that highly transparent thin films having χ(3) values of the order of 10−9 to 10−10 esu can be obtained from these materials simply by spin coat casting followed by irradiation or thermal polymerization of the diacetilenes in the polymers, or by irradiation at temperatures above the melting points, for the diacetylenes which undergo polymerization in the molten state. The important advantage of such methods is the simplicity of their processing into thin films. There is a good possibility of increasing the χ(3) values and improving the optical quality of the film by molecular designing and by further experimentation with the preparation conditions.

Steady-state photoconductivity in a novel solution-cast polydiacetylene film

Steady-state photoconductivity in solution-cast thin films of a polydiacetylene, ((8-butoxy carbonyl)methyl urethanyl)-1-(5-pyrimidyl)-octa-1,3-diyne (PDA-BPOD), has been investigated as a function of light intensity, applied electric field, incident wavelength and temperature. This newly synthesized polydiacetylene is characterized by a conjugating aromatic side group which is expected to play a role in the electronic properties of the system. The results are interpreted within the framework of one-dimensional Onsager theory of geminate recombination. The photoconductivity action spectrum shows a peak at 1.9 eV and direct band-to-band transition above 2.4 eV.

Ultrafast exciton dynamics in highly oriented polydiacetylene films

The nonlinear optical response in uniaxially oriented films of poly[1.6-di(N-carbazolyl)-2, 4-hexadiyne], epitaxially grown on a potassium acid phthalate single crystal, has been measured by femtosecond pump and probe. A fast initial relaxation and the formation of long-lived species at high excitation intensities have been observed. A high third-order nonlinear optical susceptibility of 2×10−7 esu has been estimated at 627 nm. The effects of sample orientation on the relaxation dynamics have also been investigated.

The femtosecond bleaching dynamics of polydiacetylene. Transient room-temperature spectral hole-burning features

The femtosecond exciton bleaching dynamics in a thin film of polycrystalline polydiacetylene is studied using 2 eV resonant pumping under saturation conditions. A transient hole is burnt in the inhomogeneous spectrum, 20 meV below the pump energy at room temperature. Within the 100 fs excitation step, the hole is associated with two symmetric phonon replica 35 meV apart. These replica are assigned to a low-energy Raman mode strongly coupled to the exciton and characterized by large Franck—Condon factors. The differential decay of the two side holes reveals an exciton relaxation rate which is twice as fast as the ground state recovery rate of 1.1 × 10 12 s −1.

Direct Colorimetric Detection of a Receptor-Ligand Interaction by a Polymerized Bilayer Assembly

Detection of receptor-ligand interactions is generally accomplished by indirect assays such as enzyme-linked immunosorbent assay. A direct colorimetric detection method based on a polydiacetylene bilayer assembled on glass microscope slides has been developed. The bilayer is composed of a self-assembled monolayer of octadecylsilane and a Langmuir-Blodgett monolayer of polydiacetylene. The polydiacetylene layer is functionalized with an analog of sialic acid, the receptor-specific ligand for the influenza virus hemagglutinin. The sialic acid ligand serves as a molecular recognition element and the conjugated polymer backbone signals binding at the surface by a chromatic transition. The color transition is readily visible to the naked eye as a blue to red color change and can be quantified by visible absorption spectroscopy. Direct colorimetric detection by polydiacetylene films offers new possibilities for diagnostic applications and screening for new drug candidates or binding ligands.

Preparation of highly oriented poly-diacetylene films with ion beam irradiation

Preparation of highly oriented poly-diacetylene films with ion beam irradiation

Yields of triplet exciton pairs in polydiacetylene films

Triplet-triplet-induced absorption has been measured in pump-probe experiments on polydiacetylene DCH films. The excitation spectrum of the induced absorption has been obtained for pump photon energies in the range 1.95–3.40 eV. Above 2.15 eV the induced absorption depends linearly on the pump intensity. Below this energy a quadratic law is valid showing that triplet excitons are produced in a two-step process for the lower photon energies.

Resonant Raman-scattering spectroscopy of polydiacetylene films at high pressure.

We studied the electronic energies and phonon frequencies of polydiacetylene 4-BCMU thin films at high pressures up to 50 kbar using Raman scattering under preresonant and resonant conditions. Pressure-induced changes in the resonant Raman scattering (RRS) include (1) hardening of the most strongly coupled phonon frequencies, (2) dispersion of the RRS frequencies with the laser excitation ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}}$, which shift to lower energies in analogy with the red shift of the absorption band at high pressures, and (3) softening and narrowing of the phonon distribution. These observations are consistent with an increase in the average conjugation length with pressure. Amplitude-mode-model analysis of the RRS data shows that the bare phonon frequencies increase with pressure, but otherwise the one-dimensional Peierls-type relation between the phonons and the electronic gap changes very little with pressure.

Surface patterns on single-crystal films under uniaxial stress: Experimental evidence for the Grinfeld instability.

We study the stress relaxation in single-crystal films of polymerized polydiacetylene, in epitaxy with their monomer substrate. Polymerization induces a uniaxial stress. Two types of surface patterns are observed and studied by atomic force microscopy: films thicker than 175 nm exhibit quasiperiodic cracks perpendicular to the polymer chains; thinner ones exhibit regular wrinkles with the same orientation. The wrinkle surface deformation is stress relaxing and plastic. We show that all experimental results, in particular, the order of magnitude of the pattern spacings, are compatible with the following interpretation: as polymerization proceeds, the uniaxial stress generates a Grinfeld instability (Dok. Akad. Nauk SSSR 290, 1358 (1986) [Sov. Phys. Dokl. 31, 831 (1986)]) fed by surface diffusion. The crack pattern is a secondary instability, initiated at the sites of stress concentration provided by the wrinkles.

Polydiacetylene monolayers functionalized with amino acids

Monomolecular polydiacetylene films have been constructed from a series of lipid monomers functionalized with amino acids. A wide range of surfaces including plastics, glass, and metals can be conveniently coated with peptides using these films. The techniques of X-ray photoelectron spectroscopy, fluorescence microscopy, and contact angle measurements were used to characterize the films. These studies indicate that the amino acid head groups are localized at the film-ambient interface and suggest that the films are structurally ordered both laterally and vertically. Thus, polydiacetylene films may provide promising model systems for investigating the fundamental properties of interfaces. 17 refs., 3 figs.

Quasi-epitaxial growth of diacetylene films by vacuum deposition

The quasi-epitaxial growth of vacuum-deposited films of diacetylenes on various substrates, including uniaxially aligned polymer surfaces formed with rubbing treatment or Langmuir–Blodgett technique, is reported. The oriented polydiacetylene (PDA) films are readily obtained from these monomer films using photopolymerization. Highly oriented PDA films with excellent optical qualities have been obtained on rubbed polyethylene terephthalate surfaces. The typical dichroic ratio of these oriented PDA films is more than 100:1. This ratio is high enough to permit the application of these films to optical waveguide devices. The method for obtaining these highly oriented PDA films is described in detail. In addition, the structure, the morphology, and the optical anisotropy of these PDA films is examined by x-ray and electron diffraction, electron microscopy, and other optical means.

Fast photoconduction in Langmuir-Blodgett multilayers of polydiacetylenes

The motion of charge carriers in Langmuir-Blodgett (LB) multilayers of polymerized 10,12-penta-cosa-diynoic acid (12-8 PDA) has been observed. The carriers, created between surface electrodes by light pulses of 25 ps duration from a frequency doubled Nd-YAG laser, move in a quasi 2-dimensional manner in the plane of the polydiacetylene (PDA) film under the influence of an externally applied electric field. The electric field dependence of the measured charge, Q, is found to be linear and is consistent with 1-D Onsager theory of carrier generation. The variation of Q on light intensity, I, is dependent on the gap width d, varying as Q = I m with m ≅ 0.7 for large d and m ≅ 1 for small d; this behaviour is believed to be the result of using surface measuring electrodes. Carriers transit distances are 80 μm or more, and are not, on a time scale of 10 ns, stopped at domain grain boundaries. A lower limit of the carrier drift velocity is estimated to be v ⩾ 8 × 10 3 m s which is substantially higher than that found in single crystal PDA toluene sulphonate (PDATS).

All-Optical Switches and All-Optical Bistability by Nonlinear Optical Materials

ABSTRACTAll-optical switches and all-optical bistabili ties are realized by waveguide structures with vacuum evaporated polydiacetylene(PDA) films. The basic structure of the all-optical switches are prepared in the form of layered waveguide directional coupler with vacuum evaporated PDA top layer. Clearly switchings are observed at 1064nm of pulsed Nd:YAG laser. Furthermore ultra-high speed switching with Ti;Safire 135fs laser are recognized.Operations of all-optical bistabilities are carried out by nonlinear coupling at grating structures in waveguides with PDA top layers. Hysterisis curves of bistability are affected by coupling parameters of gratings and parameters of waveguides.

Analysis of excitonic resonant effect in the third-order nonlinear optical susceptibility of polydiacetylene films

The third-order nonlinear optical properties have been investigated on the oriented blue- and red-form films of alkyl-urethane-substituted polydiacetylenes, by means of third harmonic generation (THG) and electro-absorption (EA) measurements. The spectra of |x (3) (−3ω;ω,ω,ω| and Im x (3)(−ω;0,0,ω) have been evaluated from the respective measurements. The results are discussed in terms of a three level model for quasi-one-dimensional excitons on the polymer backbone chains.

Effects of polymerization yield on photochromic properties of polydiacetylene films

Photo-chromic properties have been investigated on polydiacetylene (PDA-12,8) films, at various yields of polymerization. The curves of photo-chromic conversion vs. light irradiation dose become steeper as the polymerization yield becomes higher. All the curves show a threshold, below which the photo-chromic conversion cannot take place. From these results, we suggest that the photo-chromic conversion process in PDA-12,8 films is a cooperative phenomenon, in which an interchain interaction is playing an essential role.

Studies of resonant Raman scattering in polydiacetylene films

The disorder in polydiacetylene films cast from solution is studied by Raman scattering under preresonance and resonance conditions in both Stokes and anti-Stokes configurations. The disorder-induced inhomogeneities in the excited energy level and the strongly coupled vibrations cause strong dispersion of the CC and CC stretching frequencies with the laser excitation photon energy. We show, however, that the complete inhomogenously boardened phonon distribution is revealed when the excitation is not in resonance. In addition to the excitation resonance, resonances associated with the Stokes and anti-Stokes emission beams strongly affect the measured Raman profiles.

Cast polydiacetylene films from diacetylenic glutamate lipids

Cast polydiacetylene films from diacetylenic glutamate lipids