Synthetic Metals 146 (2004) 43–46 Electrical properties of polyunsaturated natural products: field effect mobility of carotenoid polyenes  Robert R. Burch ∗ , Yu-Hua Dong, Curtis Fincher, Marc Goldfinger, Pierre E. Rouviere E.I. duPont de Nemours and Co., Central Research and Development, P.O. Box 80328, Wilmington, DE 19880-0328, USA Received 9 January 2004; received in revised form 20 April 2004; accepted 7 June 2004 Available online 7 August 2004 Abstract Carotenoids are polyacetylene-like natural products with substituents that enhance stability, solubility, and processing. Measurements on a set of five carotenoids show bixin and -carotene to be active as field effect semiconductors, with p-type mobilities in the range of 10 -6 to 10 -7 cm 2 /V s. The structural characteristics responsible for distinguishing between active and inactive compounds are not apparent at this time. However, biosynthetic means of making carotenoids may make available a large number of carotenoids, both natural and unnatural, suggesting that carotenoids could be a rich source of different field effect semiconductors. © 2004 Elsevier B.V. All rights reserved. Keywords: Carotenoids; Polyacetylenes; Field effect mobility; Organic semiconductors 1. Introduction Carotenoids are polyenes produced by certain bacteria and plants from the isoprenoid pathway [1]. Natural functions of carotenoids include pigmentation, light harvesting in photo- synthetic processes, and oxidative stabilization [1]. A typi- cal carotenoid structure is that of lycopene, which is shown below. Its chemical similarity to electrically conductive or semiconductive organic molecules, such as polyacetylene, is clear. The similarity in structure suggests that the carotenoids could themselves be electro-active, like polyacetylene. How- ever, the carotenoids are soluble, discrete compounds, in con- trast to the intractable, unstable polyacetylenes.  DuPont Contribution Number 8502. ∗ Corresponding author. E-mail address: robert.r.burch@usa.dupont.com (R.R. Burch). The importance of detailed control of structure to per- formance as a field effect semiconductor is known, such as with regio-regular polythiophenes [2]. Soluble, film-forming polyunsaturated organic molecules that can be inexpensively printed on plastic substrates may enable important new appli- cations such as plastic electronics [3]. In these applications, the polyunsaturated organic molecules function as the semi- conductor in field effect transistors. The key figure of merit is the mobility (μ) which is a measure of how fast the charge carrier can migrate through the bulk of the material and limits both how much current can flow through the transistor and at what frequencies the transistor can operate. The charge carriers can be either holes (positive, p-type) or electrons (negative, n-type), as described elsewhere [3]. There are a large number of ways to tune carotenoid structure, including: chain length, length of the polyene run [4], end-group composition, and substituent group, as well as preparation of asymmetric polyenes [5]. These are difficult transformations to achieve using traditional chem- ical modification of the polyene backbone [4]. We therefore reasoned that, if carotenoids can be used in field effect devices, then biosynthesis could enable testing of a large 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.06.014