Rapid Access to Polychlorodiacetylene Single Crystals through H‑Bond Templating and Computations on Helical PDA Oligomers

Until
now, only two structures of polyhalogenodiacetylene (PXDA)
have been reported in the literature: polydiiododiacetylene (PDIDA)
and polydibromodiacetylene (PDBDA). Herein we report the first example
of the synthesis and topochemical polymerization of chlorodiacetylene
(ClDA) to afford the single crystal X-ray diffraction (SCXRD) structure
determination of polychlorodiacetylene (PClDA). A unique H-bonded
network was exploited to achieve polymerization. The latter is parallel
and close to the conjugated backbone, which constitutes the first
clear single crystal example of this kind of system. Comparative DFT
computational studies between the torsional potential on a model oligoClDA
with the parent nonhalogenated compound were also performed. Finally,
the capacity of the H-bonded network to induce helicity in the PDA
chains was evaluated using semiempirical tight-binding calculations.
The present work should contribute to the understanding of the exceptional
optoelectronic properties of PDA associated with the presence of delocalized
p-electrons in their backbone, with multiple possible sensing applications
and electronic device conception, among many other possibilities.