A series of symmetric derivatives of
4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran
(DCM laser dye) has been synthesized, and the nonlinear optical
properties and thermal decomposition temperatures
of each of the chromophores has been measured. The symmetric
chromophores all have larger hyperpolarizabilities
than one would expect based on their absorption maxima.
Estimations of their oscillator strengths based upon
UV/vis spectra are all well above 1.0. It is proposed that these
compounds possess two excited electronic states close
to each other in energy, both contributing to the hyperpolarizability
in an additive fashion. Electro-optical absorption
spectroscopy data and semiempirical calculations on a model compound
support this hypothesis. The implications
of these results with regard to the tradeoff between nonlinearity and
transparency are discussed. The large dipole
moments and high decomposition temperatures of these chromophores make
them attractive candidates for use in
electro-optic polymers.
A series of conjugated donor−acceptor trienes in which
the central double bond is
incorporated into an unsaturated isophorone, verbenone, or chromone
ring has been
synthesized. In each case, the donor group consists of an amine
and an aromatic or
heterocyclic ring system, and the acceptor is the dicyanomethylidene
group. The nonlinear
optical properties of each of the compounds has been measured and
correlated with its
structure. The dipole moments and molecular hyperpolarizabilities
of these compounds,
like those of other conjugated polyenes, are large enough to be used as
the active components
of electrooptic polymers. Unlike other donor−acceptor polyenes,
however, these compounds
exhibit the thermal stability required for such
applications.
The selection process leading to the development of a guest±host electro-optic material based on an amorphous polycarbonate (APC) is described. The optical loss at 1300 nm of this material system is under 2 dB/cm, which is the confidence limit of the slab measurement used. A Mach±Zehnder modulator fabricated using the push±pull poling technique has a low switching voltage (V p ) of 1.2 V.
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