Advances: Organic Metals and Conductive Polymers

"Here is a more curious case: white cats, if they have blue eyes, are almost always deaf.", Charles Darwin

Organic metals and conductive polymers span from quantum mechanics to human disease. For example, Darwin's deaf white kitty illustrates a macro quantum phenomenon. This is strong electron-phonon coupling in potent sound-absorbing organic semiconductors such as inner-ear melanin. Likewise, these materials promise exciting new technology such as organic light-emitting diode ( OLED ) displays, as well as literal "printed" circuits. Finally, the conducting polymer melanin figures in (e.g.) melanoma, deafness, and Parkinson's disease.

Revisionist History

In 1963, Australians BA Bolto, R McNeill and DE Weiss reported passive high conductivity in iodine-"doped" oxidized polypyrrole. A copy of their paper is posted Here. They achieved a conductivity of 1S/cm. These authors also described the effects of iodine doping on conductivity, the conductivity type (n or p), and electron spin resonance studies on polypyrrole. Likewise, these authors noted an Australia patent application (5246/61, June 5, 1961) for conducting polypyrrole. Typical for this field, this paper was too early and was "lost" for decades.

Meanwhile first we and then Shirakawa et al rediscovered the interesting electrical properties of the oxidized acetylene blacks. For an interesting example of convergent discovery, compare Shirawa et al's original paper to that of Bolto et al. In their defense, we did not know about this paper either until very recently, though we did suspect something like it might be out there. It just did not make senes that we should show high conductivity in an active device without somebody showing passive high conductivity first.

a. b. c.

a. Melanin, a Typical Polyacetylene (Nicolaus)
b. Melanin Bistable Switch-- First Organic Electronic Device ?.
c. Voltage-Current Relationship for Melanin Switch
, ( copyright AAAS, 1974 ) . Also note the negative differential resistance (NDR).

I.e., melanin is a synonym for polyacetylene and vice-versa. In retrospect, melanin researchers first defined much thought "new" in this area, e.g., polyacetylene photoconductivity. Further, many tissues involved in energy transduction and/or electrical activity contain melanin, e.g., the inner ear, brain, and eye. So likely nature first discovered the interesting electrical properties of polyacetylenes.

In this context, the bistable switch above is just the first of three decades of non-biological electronic devices which use some "Melanin" as an active element. It now goes to the Smithsonian chips collection labeled as "organic semiconductor, 1973", "Organic Semiconductor (I/O), 1973 a melanin (polyacetylenes) bistable switch.".

Thus, Melanin is the first organic semiconductor used in an active electronic device, i.e., one where an electric field modulates current flow. This was a bistable switch, the basic element of computers. Coincidentally, this means melanin is also the first organic material to show "metallic" high-conductivity. It was also the first organic semiconductor used in an energy storage ( " battery " ) application. The melanin switching curve also clearly shows negative differential resistance or *NDR", a fundamental property in molecular electronics. For full patents, go to US patent 4,366,216 and US patent 4,504,557.

Go Here for a slide-show on how this relates to treatment of melanoma.

Here are some links.

2000 Nobel Prize in chemistry -- " For the discovery and development of high conductivity polyacetylene derivatives."

Organic Active Devices: Transistors, Switches, etc.

Switching in Melanins A "lost" organic semiconductor device from 1974, --- the same basic active element as later devices, published in Science, then reviewed in Nature. In retrospect, names count-- the equivalent " Switching in Polyacetylenes " would have been a better title. Some pictures.

This gadget is now in the Smithsonian American Museum of History Collection

An important "lost" paper: BA Bolto, R McNeill and DE Weiss, Electronic Conduction in Polymers. III. Electronic Properties of Polypyrrole, Australian Journal of Chemistry 16(6) 1090 - 1103 (1963). PDF.

Resistance as low as 1 ohm-cm2 in oxidized iodine-"doped" polypyrrole. Likely, the first demonstration of high conductivity in the "melanins".

James Tour's Lab at Rice.Molecular switches, Nanotechnology stuff, etc..

Sir Nevill Mott on melanins ( and thus on "polyacetylenes" in general ) " So like and yet so unlike the chalcogenide switches ". Dr. Mott won the 1977 Nobel in physics for his work on disordered materials. Present models for conduction in organic semiconductors derive from his work.


Photoconductivity in melanins.


Many Organic Semiconductors are Natural Products

The Function of Melanin

Why electronic processes are important in disease

Britanny Spears Guide to Semiconductor Physics ( No kidding )

CalPoly Polymer Electronics Lab ( many good links_)

Intelligent Polymer Research Institute

Big Trouble at Bell Labs: Science Fraud involving Organic Semiconductors

Organic Semiconductors

Keywords: Organic semiconductor organic metals hopping melanin polyacetylene polypyrrole conductive polymers polyaniline conductive organic semiconductors organic polymers.