Light-Emitting Polymers and Electroactive Materials

Typical responses for second-order effects are values in the range of 0.2-20 X 10 esu. Williams (60) remarked that uniquely useful applications for organic and polymeric materials will require a of esu or greater. In addition, a variety of additional application-dependent properties and attributes must be present. These include uniform birefringence, minimized scattering losses, transparency, stability, and processibiUty. The relaxation time of the poled structures must be increased significantly. 

Another recent discovery of the interaction of polymers with electricity involves polymers that emit fight. Electroluminescence, EL, the generation of fight by electrical excitation, is a phenomenon that has been seen in a wide range of semiconductors. It was first reported for anthracene singe crystals in the 1960s. The basic phenomenon requires the injection of electrons from one electrode and holes (i.e., the withdrawal of electrons) from the other, followed by the capture of the now oppositely charged carriers by recombination. This capture produces a radiative decay of the excited electron-hole state produced by this recombination process (76). 

The EL spectrum of another new polymer is shown in Rgure 14.21 (79). Its fluorescence quantum efficiency was measured to be 63%, with peaks at 445 and 473 nm. 

Recently, new polymers have emerged that respond to electrical stimulation with a significant shape or size change. This section will briefly describe several such effects. 

Typically, PVDF is produced in the form of thin films of approximately 1 x 10 mm thickness. A thin layer of nickel, copper, or aluminum is deposited on both surfaces of the film to provide electrical conductivity when an electrical field is applied, or to allow measurements of the charge induced by mechanical deformations (81). 

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