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  • Author: E. Fonavs x
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The optically induced switching of electrical properties of indandione type molecules, which consist of acceptor and donor groups, are investigated. Both calculation and experimental results show a reversible highly dipolar photoinduced intramolecular electron transfer in 2-(4'-N, N-dimethylaminobenzyliden)indan-1,3-dione molecule (DMABI). Kelvin's probe technique is applied to investigate the surface potential of a host-guest polymer film with four different DMABI derivatives. The derivatives have been chosen to compare the influence of the geometry, concentration and dipole moment of a molecule in the ground and excited states on the response time and amplitude of photoinduced surface potential. It is shown that the time of fast response (up to several seconds) to irradiation is independent of the concentration of molecules in a polymer film. Dependence of the amplitudes of photoinduced changes in the surface potential on the molecules concentration is observed for DMABI and its three derivatives. The optimal concentration of guest molecules in the polymer matrix is in the range 10-25 wt% (depending on the molecule).

Chromofore Poling in Thin Films of Organic Glasses. 1. Overview of Corona Discharge Application

The introductory article in a series of works on the chromofore poling in thin films of organic glasses presents an overview of corona discharge applications, with a brief excursion into physics of the phenomenon. The authors consider this technique as related to the nonlinear optical (NLO) polymers. Its key points are as follows.

In the ambient air such discharge is strongly affected by variable humidity and, consequently, uncertain concentration of the predominant charge carrier ((H2O)nH+). To realize a repeatable poling process the composition of discharge atmosphere should be controlled (e.g. for pure nitrogen gas). In the case of discharge in N2 the highly reactive ozone production could be avoided. To obtain second-order nonlinear activity of polymeric materials, a simple point/plane (two-electrode) technique of corona charging is successfully applied, which however does not provide information about the sample surface charge buildup and the efficiency of poling process. To study the dynamics of both the poling and the charge transport processes a three-electrode charging system - the corona triode - should be used.

Photoisomerization Processes of Azobenzene Compounds in Thin Poymer Films

One of the most important properties of the molecular switches is turning of a molecule by external action, e.g. by irradiation with light of definite wavelength. The molecules of promise for the molecular switches are those with azobenzene moiety. When azobenzene is irradiated with light of definite wavelength, it is possible to observe the process of trans/cis isomerisation. In this work, the influence of photoisomerisation processes on the changes in the surface potential of a novel azobenzene compound is investigated.

We have studied the surface potential of a PMMA polymer film with polar azobenzene derivative of different concentrations. To orient azobenzene molecules in the film the corona poling method was used, and for studying the surface potential variations - the Kelvin probe method. The photoreaction time constant of the fast response (several seconds) was found to be almost independent of the molecular concentration in the polymer film and of the absorbed light intensity in the bulk of a sample. In contrast, the amplitude of photoinduced changes in the surface potential depends both on the concentration of azobenzene molecules and on the absorbed light intensity in bulk of the host-guest polymer film.