REDUCTIVE PREPARATION OF CARBYNE WITH HIGH-YIELD - AN IN-SITU RAMAN-SCATTERING STUDY

Electrochemical reductive carbonization of poly(tetrafluoroethylene) w ith alkali metal (Li, Na, K) amalgams leads to a polymeric carbon with a partly carbynoid structure. Raman spectra measured in situ exhibite d a strong line at around 2000 cm(-1) which was interpreted as the C=C -C stretching mode of a linear carbon chain with alternating carbon-ca rbon triple and single bonds (polyyne). The intensity and position of this line evidence an unusually high triple bond carbon content in our materials, which leads to relatively large conjugation lengths in the polyyne chains. The triple bond line shifts to higher wavenumbers wit h increasing laser energy; this can be elucidated in terms of the conj ugation length model. A quantum chemical calculation for transition en ergies and matrix elements of oligoynes with different chain lengths i s presented. In addition, the frequency of the Sigma(g) mode as a func tion of chain length is calculated. The conjugation lengths found corr espond to 8-14 C atoms in the polyyne chain and increase with increasi ng atomic number of the alkali metal. The yield of polyyne and its sta bility against interchain cross-linking increase similarly. This suppo rts our previous conclusions about the polyyne stability which were fo rmulated on the basis of electronic conductivity and UV-vis spectra.