Synthesis of a new fully conjugated polydiacetylene i.e. poly(l,4-bis(3-quinolyl)-l,3-butadiyne) is described. Reflectance spectra of partially polymerised samples and the polymer are reported. The spectra show long wavelength absorption band at 750 nm. with the visible absorption edge above 800 nm. DC electrical conductivity measurements on pristine and Iodine doped Poly-DQ are reported. The results are discussed in terms of side group - backbone electronic interactions.

We describe the synthesis and study of the first organic polymer semiconductor superlattices designed as periodic block conjugated copolymers, (−AxBy−)m. The observed variation of electronic spectra and wavelength of the lowest energy absorption maxima with block length y are interpreted in terms of quantum confinement size effects predicted for semiconductor superlattices. The periodic block conjugated copolymers were synthesized by a two-step strategy that ensure strict control of sequence, block length and periodicity. It is suggested that organic semiconductor superlattices provide a rational and systematic approach to the molecular engineering of electronic, optical, nonlinear optical, and electro–optical properties in polymeric materials and hold promise for molecular electronics and molecular photonics.

We have measured extremely large second hyperpolarizabilities〈γxxxx〉 in solutions of two recently prepared organic polymer semiconductor superlattices. These block copolymers are of alternating aromatic and quinoidal moieties and structurally differ by a side group substituent. The values observed are 1.6 × 10−29 esu for the parent copolymer (PBTBQ) and 3.7 × 10−30 esu for its acetoxy derivative (PBTABQ). The corresponding values of χ(3) are estimated to be 2.7 × 10−7 esu and 4.5 × 108 esu. The measurements, made by picosecond degenerate four wave mixing at 532 nm, showed that the dynamics of the larger χ(3) valued copolymer were faster than the 30 ps resolution of the instrument while the derivative exhibited a slower response. The large magnitude and rapid response of the cubic optical nonlinearities in these novel materials suggest theiT potential for further development and photonic device applications.

The synthesis and second-order nonlinear optical (NLO) properties of a new family of optically nonlinear coumarin dye-containing polymers is reported. Polymerizable coumaromethacrylate (CMA) monomers having various alkyl spacers (C2 to C5) between the polymerizable group and the chromophore were prepared and copolymerized with methylmethacrylate (MMA) and other vinyl monomers. The CMA copolymers had high chromophoric content (up to 18 × 1020) and glass transitions as high as 132°C. Spin cast films were prepared on BK7 substrates and oriented by corona-onset poling at elevated temperatures (COPET). The poled CMA copolymer films were characterized for spectroscopic absorption and second harmonic properties. A comparison of the nonlinear optical properties of poled CMA-MMA copolymers to poled guest-host systems is made. Relative to guest/host systems, CMA-MMA copolymer films exhibit larger and much more stable second-order nonlinear optical properties.

New polymers incorporating a variety of electroactive moeities with defined π-electron conjugation lengths have been synthesized and characterized by degenerate four wave mixing (DFWM) techniques. The χ(3)/α values for these materials varied from 10−12 to 10−13 esu cm. This work has identified several promising structures with nonlinear optical activity including organometallic and purely organic materials. The preparation of composite materials has also permitted the measurement of χ(3)/α as a function of the electroactive unit concentration.

Nonlinear optical properties of two thiophene-based conjugated polymers (PTT and PDTB) were studied by the photoinduced absorption spectroscopy and the third harmonic generation spectroscopy. The results obtained with these two methods are used to estimate the value of χ(3) in these materials. Resonant χ(3) are (2.0 ± 0.2) × 10−11 e.s.u. and (1.0 ± 0.1) × 10−11 e.s.u. for PTT and PDTB, respectively. χ(3) is shown to be related to the width of the optical gap through a sixth-power law. In PTT a vibronic structure due to the C = C stretching mode appears in the χ(3) spectrum.

Perot Fabry interferometry under oblique incidence provides a powerful tool for the determination of the complex values of the independant components of the tensors χ2(−ω;ω,ο) and χ3(−ω;ω,ο,ο) of poled films. Deorientation of Disperse Red One chromophore in a poled film can be followed by the decrease with time of two order parameters. In the short term regime, the relaxation times of this process are spread over a broad spectrum. By comparing the chromophore dynamics in PMMA, PS and SAN at different temperatures, it appears that free volume and secondary transition concepts cannot fully explain the chromophore behavior. Chromophore dipole/Polymer dipole interactions are invoked in order to explain the slow deorientation rate in SAN.

Doped glassy polymers have been examined as potential materials for nonlinear optical (NLO) device applications[l-Il1]. In these systems, dopants with excellent nonlinear optical capabilities are dispersed in glassy polymer matrices with good physical properties to make versatile and efficient NLO materials[1-4]. The optical technique of second harmonic generation (SHG), conversion of light of frequency to to light of frequency 2o, is performed as a function of time to examine the temporal stability of NLO dopant orientation in the polymer matrix[I-4]. Through the use of poling, the NLO dopants are aligned into the noncentrosymmetric orientation required for SHG to occur[1-4,7]. Polymeric NLO materials have a number of advantages over the current commercial inorganic crystals, including ease of fabrication and processability, low laser damage, low cost, and excellent chemical and physical resistance[8-10]. Due to the relaxation behavior characterizing glassy polymers even at temperatures well below the glass transition temperature Tg, the dopants can disorient as a function of time following poling[1-4,12,13]. This results in a loss of optical performance with time. The purpose of this work is to examine the basic polymer physics that govern the temporal stability of the dopant orientation and disorientation and related optical behavior as a function of the local microenvironment surrounding the NLO dopants. Systems studied include bisphenol-A-polycarbonate (PC), polystyrene (PS) and poly(methyl methacrylate) (PMMA) doped with well characterized NLO dyes such as 4-dimethylamino-4′- nitrostilbene (DANS) and 4-amino-4′-nitroazobenzene (or disperse orange 3, D03).

The enhancement of the third order nonlinear susceptibility χ(3)) of an homologous series of polycondensed thiophene based polymers was observed about photoinduced polaronic bands by a novel “pump-probe” degenerate four wave mixing echnique. Enhancement of the degenerate four wave mixing signal for more than an order of magnitude was achieved with response time of less than 25 ps. The intrachain polarons contribution is proposed as the possible mechanism responsible for the observed enhancement.

Poly(2,5-thienylene vinylene), PTV, can be conveniently prepared via a precursor route to give coherent films suitable for optical measurements. Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 eV and 1.0 eV that are associated with bipolarons that live for times of order a few ms at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. Pump and probe measurements of the induced bleaching at 2 eV show a very fast rise and initial fall time, which are within the 100 fsec resolution of the measurement.

A bilayer of a surfactive polydiacetylene (15–8 PDA) has been deposited by Langmuir-Blodgett technique on a smooth Silicon substrate using a commercial Lauda film balance [1] . The morphology of the deposited film has been studied by cross-polarized optical microscopy, and laser light scattering microscopy. Usual crystalline domains with size ranging from 5 to 50 μm can be seen between cross polarizers. Nonuniformities and voids in the film are observed by imaging the scattered light from a visible laser beam incident at grazing angle onto the film.

Raman scattering study on these bilayers have been carried out to investigate their vibronic structure. Information about vibronic levels from PDA has been used to define the extent of disorder and crystalline phase of the bilayer.

Electronic excitation energies and transition dipoles measured for symmetrically substituted linear polyenes (R-(CH=CH)N-R) with chain lengths n ranging from 2 to 8 are well fit by the functional form A+B/N. Extrapolation to the long chain limit correlates the band gap transition of polyacetylene with the polyene 11Ag to 11Bu transition. The amount by which the highly correlated polyene 21Ag state is lower than the 11Bu state increases with increasing chain length, extrapolating to roughly half of the 11Bu excitation energy. The 11Ag to 11Bu transition dipole magnitude per chain repeat unit attains a maximum value of 3.0 Debye at an effective conjugation length 5 double bonds.

Careful studies on linear polyenes provides insight into the electronic structure of polyacetylene.

Theoretical calculations on nonlinear susceptibilities of organic crystals are made. Under the oriented gas model approximation, nonlinear susceptibility of a crystal can be calculated both from the molecular hyperpo1arizability and crystal structure data. Molecular hyperpolarizabilities are calculated by an ab initio molecular orbital (MO) method and the energy minimum crystal structures are obtained by an empirical atom-atom pairwise potential method. Finally the effect of intermolecul ar interactions on molecular hyperpolarizabilities, which is neglected in the above approximation, is investigated quantitatively by using a “super molecule” method of ab initio MO calculations.

For several cross-conjugated molecules, molecular excited states and third-order nonlinear susceptibilities γ are calculated by semi-empirical molecular orbital method. The calculated γ are compared with each other and the reason for the differences are discussed in terms of the orbital shapes which contribute mainly to γ. The reason that long polyene chains have large γ, is ascribed to the large transition moment which is explained by the signs of the LCAO coefficients. On the other hand, it is found that the cross-conjugated molecules in which two similar-length chain cross at the center is not good for large third-order susceptibility.

Quantum lattice fluctuations of conjugated polymers in the form of virtual soliton-antisoliton pairs have important effects on the nonlinear optical properties. Quantitative calculations of nonlinear susceptibilities based on the solitonic molecular model are presented.

This paper will present quantum calculations on the L-arginine part of the nonlinear crystal L-arginine phosphate. The emphasis here will be on understanding the NLO properties in terms of the excited states of the system and accompanying charge movements in these excited states. Both the carboxylate and the guanidyl ends of the molecule contribute to the values of β. The guanidyl seems to be the bigger contributor, but the contribution varies with the particular tensor component. The properties of the crystal will not be discussed here.

The electronic structure of organic and inorganic polymeric systems are well described in terms of their molecular symmetry, even with the large bond polarity shown by such systems as polyphosphazenes. We have performed calculations using the semi-empirical CNDO/1 method to determine the valence electronic structure for a series of model phosphonitrilic and organic compounds. The optical transition energies for phosphonitrilic compounds are greater than their organic counterparts as a result of in-plane π’ bonding interactions. The extent of these interactions is modulated by the electronegativity of the substituent groups on the phosphorus atoms. We report values for the vertical ionization energy and electronic absorption wavelengths, and use molecular orbital contour analysis to show the effects of ligand electronegativity on the π’ network.

The dielectric function of inhomogeneous materials is composed of linear and nonlinear responses which are sensitive to the film microstructure as well as the intrinsic properties of the materials. We have developed a method to self-consistently determine the linear and non-linear contributions to the dielectric function of films with random microstructure. This method is based upon a numerical solution of the general electrostatic equations and is applicable to arbitrary shapes and orientations of model defects. This method provides near exact solutions to the linear response of the dielectric function. We have shown that the nonlinear part of the dielectric function is extremely sensitive to the void shape and void fraction.

The structures of the mixed LB monolayers, composed of two different kinds of π-conjugated system, poly(3-hexylthiophene) (PHT) and pentacosa-10, 12-diynoic acid (DA), have been investigated mainly by a second harmonic generation (SHG) Maker fringe method. The mixed LB films partly contain a double-layered structure consisting of PHT and DA. The second harmonic radiation has been produced from slightly twisted PHT in the double layer. Both UV-polymerization of DA and successive heat-treatments enhanced the SHG intensities. The enhancement of the SHG intensities has been elucidated by the enlargement of the PHT twisting and the interaction between PHT and a newly formed π-conjugated system.

Hydrazone, 1,1-dimethylhydrazone, methylhydrazone, phenylhydrazone and p-nitrophenyl hydrazone derivatives of substituted aromatic aldehydes were prepared and screened for second harmonic generation using the Kurtz powder technique. One compound, 4-nitro-3-methoxybenzaldehyde hydrazone exhibited a second harmonic signal up to 32 times that of ammonium dihydrogen phosphate (ADP) and 4-nitrobenzaldehyde hydrazone exhibited a second harmonic signal five times higher than previously reported, up to 40 times that of ADP. 3-methyl-4-nitrobenzaldehyde hydrazone, 4-nitrobenzaldehyde phenylhydrazone, 1-naphthaldehyde phenylhydrazone, 1-pyrenecarboxaldehyde phenylhydrazone exhibited second harmonic signals 25, 2.5, 5 and 20 times that of an ADP standard.