The conversion of the complex salt of TCNQ and triethylamine; TEA(TCNQ)2 into the zwitterionic NLO chromophore DEMI can be achieved in a polymeric guest host system. Synthesis of the chromophore in a thin polymer film can be monitored by observation of the SHG in an in-situ poling experiment. We discuss the characterization of the conversion process, which could potentially lead to the "writing" of very small areas of nonlinearly active material into otherwise inactive polymer films. We have found that the transformation from organic salt to NLO (Non linear Optical) chromophore occurs at approximately 160°C, the transformation is accompanied by a dramatic change in colour from green to blue and by an accompanying decrease in conductivity. The resultant blue spectrum is identical to that obtained by doping DEMI into PMMA. All characteristic TCNQ- peaks in the UV/Vis absorption spectrum are completely diminished, and the reaction appears to be almost 100% efficient. In-situ corona poling experiments, while heating a thin film of TEA(TCNQ)2 in PMMA above its glass transition temperature reveal no SHG from an input wavelength of 1.9 microns until the conversion temperature is achieved. At this point when DEMI has been "synthesised" in the sample the SHG can be observed and its relative intensity measured relative to that of a quartz plate. We also discuss the attempted synthesis in situ of a related zwitterionic NLO chromophore Me-P3CNQ.
Highly dipolar non-linear optical chromophores with absorption typically in the range of 350-500 nm have been synthesized by the reactions of amines with tetracyanoquinodimethane (TCNQ). These materials show interesting fluorescence properties with the emission strongly dependent on the host environment. One of the advantages of these materials is the large figure of merit ((mu) (beta) ), which is calculated to be -765 x 10-48esu, allowing large non-linear optical coefficients to be obtained. Guest-host polymer films of these materials have been corona poled using a constant current corona triode. These materials are highly dipolar which leads to the formation of aggregates within the doped polymer films. Studies of the second order non-linearities using second harmonic generation (SHG have revealed the presence of such aggregation. The magnitude of the SHG that can be obtained form such systems is therefore severely limited by this aggregation. This phenomenon was then confirmed with optical spectroscopy and electric field induced second harmonic generation (EFISH) studies.
The dipole moments ((mu) ) of a series of zwitterionic nonlinear optical chromophores doped into poly(methyl methacrylate) have been determined. Values of between 34 D and 38 D have been measured through the fitting of a uncurtailed Langevin function to the incidence angle dependence of the p-p second harmonic intensity generated from corona poled films. It is shown that accurate values of dipole moment can only be determined when the poling fields are lower than approximately 100 MVm-1 above which existing electric field poling models appear to be inadequate. The reasons for this are as yet unknown, possible mechanisms of the effect are presented.
We report the synthesis and evaluation of new highly polar molecules whose combined non- linear and linear optical properties are of interest for frequency doubling. The generic scheme for the syntheses rests on enamine substitutions of tetracyano-p-quinodimethane (TCNQ). In the case detailed, a novel reaction product is reported from the unexpected reaction of triethylamine and TCNQ. In polar solvents such as DMF, the molecule has a charge separated ground state and a measured bipole moment of 45 D. Also in polar solvents, the value for the resonant (beta) coefficient is measured to be -190 X 10-30 esu. Coupled with acceptable transparency at 460 nm ((epsilon) equals 86 M-1 cm-1) this molecule points to a new approach in the design of such materials.
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