Linear Carbon Chains: Length Effect and Role of π-conjugated Thiophene End-Groups

In this paper, we investigate the structural and optoelectronic properties of a series of linear carbon chains (LCCs) containing 4, 8 and 12 carbon atoms, and capped by hydrogen, thiophene (1T), and bithiophene (2T) molecules as a template for sp-sp2 hybrid systems. Using DFT calculations, we present the optimized geometries of the differents free LCCs. A relative symmetry with respect to the centers of all structures is found, confirming the polyynic structure of the different LCCs. Then, we expose the correlation between the bond length alternation and the HOMO-LUMO gap of the considered LCCs. The effects of the LCCs lengths, as well as the role of end-groups in tunability of carbon chain properties are brought out. These results seem to indicate the possibility to influence the structural and optoelectronic properties of the LCCs by choosing proper π-conjugated thiophene based endgroups.