ELECTROCHEMICAL PREPARATION OF HYDROGEN FREE CARBYNE-LIKE MATERIALS

Natural carbyne-like structures (linear end-capped polyynes) occur in space and in certain biological objects. The synthetically demonstrate d species contain up to 30-300 carbon atoms; even longer chains should be accessible by electrochemical defluorination of PTFE. Cathodic car bonization of perfluorinated hydrocarbons with alkali metal (M = Li, N a, K) amalgams gives a solid composite of n-doped elemental carbon and the equivalent amount of MF. Raman spectra of C-MF show an unusually strong band at 2000-2100 cm(-1) which was assigned to the C = C stretc hing mode of polyyne (''carbyne''). The optimum synthesis of carbyne-l ike materials represents the electrochemical reduction of stretch-orie nted PTFE films with K or Na amalgams. Electrochemical polyyne is part ly stabilized against interchain crosslinking towards graphene by inte rspersed MF. A polyyne-to-graphene conversion occurs by aging in a lon g time scale (years). It can be monitored by well-defined changes of e lectronic and optical properties of C-MF. The electrochemical amalgam carbonization of highly-oriented (friction-deposited) PTFE films is su perior to the carbonization with alkali metal vapor. The product showe d larger conjugation length than that from ordinary unoriented precurs or. (C) 1998 Elsevier Science Ltd. All rights reserved.