Sina Ijadi-Maghsoodi

Synthesis and study of a polysilole

Abstract The thermal polymerization of Ph 2 Si(C≡CH) 2 reported in 1968 by Luneva et al. has been reexamined and spectroscopic analysis reveals that it does not produce the claimed structure. Different synthetic procedures yeild either a deep red polymer of molecular weight (MW ∼ 55,100 or a violet polymer of MW ∼ 105,300. Structural models and spectral examination of both systems strongly suggest that they are a polysilole of the form: If this structure is correct, this is the first example of a polymetallole with the heteroatom devoid of lone-pair electrons. The red polymer remains insulating even after doping with AsF 5 or I 2 . The conductivity of the intially semiconducting violet polymer ( σ ∼ 10 −7 S/cm), however, increases by four orders of magnitude upon doping with I 2 . Photoabsorption, photoluminescence, and ESR measurements are also described and discussed. The results suggest that this polysilole is intrinsically an insulator.

Conductivity, optical absorption, photoluminescence, and X-band optically detected magnetic resonance of novel poly(2,5-dibutoxyparaphenyleneacetylene) (PDBOPA)

Abstract The optical properties of novel PDBOPA (average molecular weight ≈ 48 000) are described and discussed. Exposure to I2 vapor at ≈80 °C increases the conductivity to ≈5 × 10−3 S/cm, but the I2 rapidly evolves from the film at room temperature. The absorption onsets at 2.53 eV and peaks at 2.81 eV. The 2.71 eV-excited photoluminescence (PL) peaks at ≈2.0 eV in films and solutions. In all cases, it is very intense and largely structureless. This contrasts with the clear vibronic structure of the PL of poly(3-alkylthiophene) (P3AT) and poly(2,5-dialkoxyparaphenylenevinylene) (PDOPV) films and blends. As in P3AT and PDOPV, three PL-enhancing optically detected magnetic resonance (ODMR) features are observed: (i) a strong narrow (≈15 G wide) resonance at g = 2.0025, attributed to intrachain polaron recombination; (ii) a ≈1.0 kG wide triplet powder pattern around g ∼ 2, and (iii) the Δms = 2 transitions of these excitons at g≊4.07 . The results are discussed in relation to conformational defects resulting from the near cylindrical symmetry of the backbone acetylene units.

Theoretical structural characterization of polydiethynylsilane - a new nonlinear optical material

Abstract Recently, a novel π-conjugated polymer, polydiethynylsilane (PDES), with excellent nonlinear optical properties has been reported. The structures of several isomeric forms for PDES have been characterized theoretically. The results show that the four-membered ring structure is the most plausible and some dialkyl, ethynylsilane groups may insert in the backbone of PDES as sequential copolymers. These results were obtained using the molecular orbital method at the ab initio level (3–21 G ∗ modified) and molecular mechanics method with potentials derived from ab initio calculations. We have also calculated the second-order polarizability.

Optical probes of polydiethynylsilanes

Abstract We have applied a variety of optical probe techniques for studying the ground-state properties, photoexcitations, and optical nonlinearities of the novel class π-conjugated polymers incorporating Si (or Ge), the polydiethynylsilanes (PDES): [(HCue5fcC) 2 SiR 2 ] x , where R = alkyl, phenyl, etc. Our measurements imply that the PDES backbone structure consists of units of four-membered rings alternately connected to CH and SiR 2 units; thus it can be regarded as an almost degenerate ground state (AB) x with a band gap at 2 eV. The PDES are therefore the second class of conducting polymers that can support soliton excitations. Using the photomodulation spectroscopy technique, we have found in PDES photogeneration of charged solitons similar to that in trans -(CH) x , as predicted by theory. However, due to the short average conjugation length in PDES films, the soliton energy levels are split by end-effects confinement. We have also found at 2 eV χ (3) = 3 × 10 − 9 esu, which decays in a record time of 135 fs, followed by a slower decay component of 750 fs, without a long tail even at higher laser intensities.