1 |
rediscovered the interesting electrical properties of the oxidized acetylene blacks. For an interesting example of convergent discovery, compare s***rawa 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 sense that we should show high conductivity in an active organic semiconductor device without somebody showing pa***ive high conductivity first. a. b. c. a. Melanin, a Typical Polyacetylene (Nicolaus) b. Melanin Bistable Switch-- First Organic Electronic Device ?. c. Voltage-Current Relations***p for Melanin Switch, ( copyright AAAS, 1974 ) . Also note the negative differential resistance (NDR). R. Nicolaus: "The most simple melanin can be considered the acetylene-black from which it is possible to derive all the others..... Subst**ution does not qualitatively influence the physical properties like conductivity, colour, EPR, which remain unaltered." from The Nature of Animal Blacks ( "acetylene-black" = polyacetylene) 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 is now part of the Smithsonian Chips collection, labeled as "organic semiconductor, 1973", (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, see 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 t**le. 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, one of the first demonstrations of high conductivity in an organic semiconductor. More from 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. Photovoltaics Conjugated polymers as photovoltaics |
image |