PHOTOELECTRICAL PROPERTIES OF INDANDIONE CHROMOPHORE IN SOLID STATE
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).
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.
Optically Induced Surface Relief Gratings in Polymer Films Doped With Sulphonyl Group Containing Azobenzene
In holography, more attractive have become azobenzene compounds doped in a polymer matrix (host-guest polymer film) or chemically attached to the polymer. Azobenzene molecules exhibit reversible photoisomerization between trans- and cis-isomers which can form a surface relief grating in the films. The authors investigate the holographic recording and formation of surface relief gratings in a host-guest polymer film with two original azobenzene compounds. Holographic recording with 325 nm laser light was performed in host-guest polymer films with the host being polymethylmetacrylate (PMMA) and the guest - 15 wt% azobenzene molecules (A-45 or A-48). In both cases an increase in the diffraction efficiency at the beginning of the process could be related to the trans-cis-photoisomerization, while the second increase - to the formation of surface relief gratings. The systems with A-45 molecules reach a diffraction efficiency of 0.7%, and with A-48 molecules - of 0.24%. Also, the depth of surface relief gratings is greater in the films with A-45 (35 to 45 nm) than in those with A-48 (4 to 6 nm) molecules.
Chromophore Poling in Thin Films of Organic Glasses. 2. Two-Electrode Corona Discharge Setup
In Part 1 of the article we provided description of the corona discharge physics and overview of the methods used for corona poling in thin organic films. Subsequent sections describe comparatively simple technical methods for poling the organic nonlinear optical polymers using a two-electrode (point-to-plate or wire-to-plate) technique. The polarization build-up was studied by the DC positive corona method for poling the nonlinear optical (NLO) polymers. The experimental setup provides the corona discharge current from 0.5 μA up to 3 μA by applying 3 kV - 12 kV voltage to the corona electrode and makes possible selection among the types of corona electrodes (needle, multi-needle, wire, etc.). The results of experimental testing of the poling setup show that at fixed optimal operational parameters of poling - the sample orientation temperature and the discharge current - the corona charging of polymeric materials can successfully be performed applying the two-electrode technique. To study the dynamics of both poling and charge transport processes the three-electrode charging system - a corona triode - should be applied.
Novel Amorphous Red Electroluminescence Material Based on Pyranylidene Indene-1,3-Dione Derivative
The organic light emitting diode (OLED) is a promising device for future technologies, like flat panel displays and novel light sources. So far the OLED structures have mostly been made by thermal evaporation in vacuum. An alternative approach is to use small molecules which form solid state with glassy structure from solutions. Such compounds can be used in the ink-jet printing technologies and result in reducing the OLED prices.
In this paper, we present an original red fluorescent organic compound 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-methyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK1), with the maximum of the photoluminescence spectrum for solid state at 657 nm. The structure of the electroluminescent device was ITO/PEDOT: PSS (40 nm)/ZWK1 (120 nm)/LiF (1 nm)/Al (100 nm). The electroluminescence spectra correspond to the CIE coordinates x = 0.65 and y = 0.34 with the maximum at 667 nm. The power and luminance efficiency at the luminance of 100 cd/m2 is 0.43 lm/W and 1.97 cd/A, respectively.