Photoconductive and Photonic Polymers

Some polymeric materials become electrically conductive when illuminated with light. For instance, poly(TV-vinylcarbazole) is an insulator in the dark, but when exposed to UV radiation it becomes conductive. The addition of electron acceptors and sensitizing dyes allows the photoconductive response to be extended into the visible and NIR regions. In general, such photoconductivity depends on the materials ability to create free-charge carriers, electron holes, through absorption of light, and to move these carriers when a current is applied. 

Related to this are materials whose response to applied light varies according to the intensity of the applied light. This is nonlinear behavior. In general, polymers with whole-chain delocalization or large-area delocalization in which electrons are optically excited may exhibit such nonlinear optical behavior. 

Since the discovery of doped polyacetylene, a range of polymeric semiconductor devices has been studied, including normal transistors, field-effect transistors (FETs) photodiodes, and light-emitting diodes (LEDs). Like conductive polymers, these materials obtain their properties from their electronic nature, specifically the presence of conjugated -bonding systems. 

In electrochemical light-emitting cells, the semiconductive polymer can be surrounded asymmetrically with a hole-injecting material on one side and a low work function electron injecting metal (such as magnesium, calcium, or aluminum) on the other side. The emission of light may occur when a charge carrier recombines in the polymer as electrons from one side and holes from the other meet. 

Poly(/ -phenylene vinylene) (PPV) was the first reported (1990) polymer to exhibit electroluminescence.26 PPV is employed as a semiconductor layer. The layer was sandwiched between a hole-injecting electrode and electron-injecting metal on the other. PPV has an energy gap of about 2.5 eV and thus produces a yellow-green luminescence when the holes and electron recombine. Today, many other materials are available that give a variety of colors. 

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Osaheni and Jenekhe reported a synthesis of conjugated rigid-rod polymers and their NMR data. The conjugated rigid-rod polymers have interesting photoconductive, light-emitting and third-order nonlinear optical properties that have some potential for applications in optoelectronics and photonics. 

Typical functions of substituted poly acetylenes are based on their (i) high gas permeability and (ii) electronic and photonic properties. The former originates from the rigid main chain and bulky substituents. Though electrical insulators, substituted polyacetylenes are more or less conjugated polymers, and this feature has been utilized to develop their electronic and photonic functions such as photoconductivity, electrochromism, optical nonlinearity and ferromagnetism. 

Conjugated polymer superlattices and porphyrin arrays connected with molecular wires are superstructured materials, which exhibit unique optical and photonic functions. The former shows a shift in photoluminescence to higher energy which is interpreted as a quantum size effect. The latter class of materials exhibits photoconductivity by a hole carrier mechanism and photoinformation storage by a localized excitation mechanism. The syntheses of these two classes of materials are described. 

PhotMefractive (PR) polymers are multifunctional field-responsive materials that combine photoconducting and electro-optic propoties. hi this charter, we will review the basics of photorefiactivity in polymers and liquid crystals and describe recent advances that have led to highly efficient materials. These advances in material development enable a variety of photonic aiqilications including optical correlators for security verification. 

Optically active bi-functionals co-polymers poly[(S)-(-)-MCPP-co-(S)-MAP-C], poly[(5)-(-)-MCPP-co-(5)-MAP-iV] and poly[(5)-(+)-MCPS-co-(S)-(+)-MOSI] were synthesized and their stmctural characterization were made. The application of this synthesized polymers are found in chiroptical switches, photoconductive as well as photorefractive and photonic materials for NLO and optical storage. 

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