Poly(cyanoacetylene): a conjugated polymer with a rich phase diagram

Density-functional calculations on a single, isolated, infinite, periodic c hain of poly(cyanoacetylene) have been performed. Thereby more different st ructures have been considered, partly differing in bond-length-alternation patterns and partly differing in whether the system has a polyacetylene-lik e or a polyacene-like structure. It is found that all structures with a bon d-length alternation are stable, that the systems are semiconductors, and t hat the polyacene-like structures are the stablest ones. Finally, the conse quences of these findings for excitation and transport processes are discus sed, and an interesting charge separation for the polyacene-like structures is found. (C) 2001 Elsevier Science B.V. All rights reserved.