摘要:

Unsymmetrica11y substituted diacety1enes (1–5) with a mesogenic core on one side were prepared. As a substituent on the other side was introduced para-substituted benzenesulfonyl group, which is a substituent of symmetrically substituted diacetylenes PTS and PCS. Both diacetylene monomers1and2. were found to polymerize by heating in solid state with a similar reactivity, which shows a sharp contrast to a large difference in reactivity between PTS and PCS. Hydroxymethyl derivative3polymerized in both crystal state and liquid crystal state. Characteristic reaction behavior of3in a nematic phase was elucidated. Other examples of reactive unsymmetrical monomers are presented.

ISSN:1058-725X    

DOI:10.1080/10587259208046877

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Optical spectra (ordinary absorption, photoluminescence, electro‐absorption, and two‐photon absorption spectra) have been investigated for thin films of polysilanes with a variety of backbone conformations such as trans planar, alternating trans-gauche, helical, and disordered forms. The results observed have revealed new features of one‐dimensional exciton states characteristic of each conformation of the polymer backbone.

ISSN:1058-725X    

DOI:10.1080/10587259208046878

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Third‐order hyperpolarizabilities (γ) of silicon compounds are calculated by theab initiocoupled-perturbed Hartree‐Fock (CPHF) method. The basis set dependencies of the γ‐values are first examined. The γ‐values calculated for Si compounds by CPHF (6–31G+PD) are compared with those of corresponding carbon compounds.

ISSN:1058-725X    

DOI:10.1080/10587259208046879

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The resonant optical nonlinearity in pseudoisocya‐nine J‐aggregate is investigated. Large degenerate four wave mixing signals and negative absorption changes at the wavelengths corresponding to J‐aggregate absorption band are observed. It is concluded that the origin of the large optical nonlinearity is mainly due to the absorption saturation of J‐band. The mechanism of the absorption saturation is discussed on the bases of exciton delocalization effect.

ISSN:1058-725X    

DOI:10.1080/10587259208046880

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Ultrafast optical response in polydiacetylenes and polythiophense was investigated by femtosecond time‐resolved absorption spectroscopy. Several nonlinear optical processes, i.e. hole burning, Raman gain, and induced‐frequency shift, were observed and the third‐order nonlinear susceptibilities were determined. The ultrafast relaxation dynamics following after the photoexcitation was investigated and the formation and relaxation of self‐trapped exciton was observed. A model of the relaxation processes of excitons in conjugated polymers is proposed. The short life of STE and difference between fluorescent and nonfluorescent polymers are explained.

ISSN:1058-725X    

DOI:10.1080/10587259208046881

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The surface symmetry of hemicyanine monolayer and merocyanine monolayer is studied by surface second‐harmonic generation. While the monolayer consisting of dye monomer has C∞v, symmetry with the rotation axis along the surface normal, the monolayer containing J‐aggregated merocyanine has C2vsymmetry whose rotation axis lies in the surface plane. This anisotropy in the surface plane is diminished by heating due to the dissociation of the J‐aggregates.

ISSN:1058-725X    

DOI:10.1080/10587259208046882

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An assessment has been made of the linear electro‐optic effect in single crystals of NMBA. Half‐wave voltages of 1.1–2.8 kV have been determined in the spectral range 488–632.8 nm. Such low values are appropriate in a material which shows well aligned molecular dipoles in the crystalline state and define its potential for use as a modulator material.

ISSN:1058-725X    

DOI:10.1080/10587259208046883

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

α-sexithienyl (T6) is a large rigid rod molecule with twelve conjugated double bonds. The electronic structure of T6has been investigates by one-photon and two-photon spectroscopy as well as by photoconductivity. From the single crystal polarized spectra at 4.2K we observe that the lowest allowed π-π transition (λmax= 478 nm) is polarized parallel to the long molecular axis and a second intense transition at 370 nm is polarized parallel to the short in plane axis. The two-photon excitation spectra in polycristalline thin films have been investigated at 4.2 K in the spectral range between 910 and 1180 nm of the fundamental laser radiation. The intense two-photon absorption band at 544.9 nm is assigned to the 2lAg exciton band origin. The lowest “gerade” exciton level lies therefore at 898 cm−1above the lowest one-photon allowed 11Buexciton level. The photophysics of T6is studied by photoconductivity and one-photon excitation spectroscopy. An efficient pathway for carrier generation open up at energies in the proximity of the 21Agexciton. We suggest that T6is a good model compound for polythiophene (PT) and therefore the energetics of PT should be very similar to T6.

ISSN:1058-725X    

DOI:10.1080/10587259208046884

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Controlled picosecond time‐domain interference of photochemically accumulated stimulated photon echoes excited by different laser pulses have been analyzed theoretically and observed experimentally in octhaethylporphin‐doped polystyrene at 2K. The methods of segmentwise storage and reconstruction of light signals in a selected time interval and performing operations af addition and subtraction have also been demonstrated. Potential applications of observed

ISSN:1058-725X    

DOI:10.1080/10587259208046885

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

All experimental data available on a low‐temperature optical dephasing for H,‐octaethylporphin guest molecules in an amorphous polystyrene host are discussed in relation to spectral diffusion processes. Some data published earlier have once more been thoroughly studied and some corrections introduced, also some new data are presented. A notable dependence of the holewidth on a burning wavelength within the inhomogeneously broadened 0–0 absorption band at T = 0.05 K has been observed. The spectral diffusion is found to be actual at T = 1.45 – 7 K and is not at T< 0.05 K and at T>8 K.

ISSN:1058-725X    

DOI:10.1080/10587259208046886

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor