Ion exchange in (BO) 2.4 I 3 microcrystals: A method for obtaining colorless, transparent, metallically conductive polymer films

I obtained colorless, transparent, metallically conductive polymer films by anion exchange in the microcrystals of (BO) 2.4 I 3 [BO = bis(ethylenedioxytetrathiafulvalene)], forming the conductive network in surface‐conducting reticulate‐doped polycarbonate (PC) films. Strongly absorbing I 3 − anions were replaced by I − or Br − anions, showing weaker absorption in visible light. Interestingly, this transformation proceeded without deterioration of the continuity of the network, and even the shape of the microcrystals was preserved. Particularly, the salt (BO) 2.4 I 3 could be transformed to (BO) 2 Br(H 2 O) 3 or to (BO) 2 I(H 2 O) x . I achieved this by immersing strongly colored PC/(BO) 2.4 I 3 films in the KBr solution or by contact with a Cu plate in KI solution. Depending on the conditions of the ion‐exchange reaction, colorless films showing metallic conductivity down to helium temperatures or showing semiconducting behavior below 100 K were obtained. Electrical properties of some systems are very sensitive to the partial pressure of water. The (BO) 2 Br(H 2 O) 3 and (BO) 2 I(H 2 O) x microcrystals could reversibly change their water content, as shown by comparative X‐ray diffraction and electrical studies performed under reduced pressure or dry atmosphere and under ambient conditions. The controlled anion exchange presented in this article can be considered as a new effective way of modifying the polycrystalline networks of (BO) 2.4 I 3 and other similar salts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1465–1472, 2002