DFT approach on stability and conductance of nine different polyyne and cumulene molecules

Cumulene molecules are one of the main candidates for the use as molecular wires. Low bond length alternation (BLA) values are one of the main attractive property of cumulene molecules as it leads to high conductivity, whereas stability under normal conditions is the main problem. The study is aimed at achieving stable molecules with low BLA values by forcing cumulene structure in polyynes through substitution. Hence, we considered symmetric LCC molecules of n core carbon atoms (n = 4–12) with nine different terminal groups substitution such as hydrogen terminated polyynes (H[n]), phenyl terminated polyynes (Ph[n]), pyridine-capped polyynes Py[n], 3, 5-diphenyl pyridyl terminated polyynes (Py*[n]) their hydrogenated forms (H-Py[n] and H-Py*[n]), oxygen substituted phenyl terminated polyynes (O=Ph[n]) and 2, 4, 6-trimethylphenyl capped cumulenes (Mes[n]). The BLA values, transport barrier, excitation energy, reorganisation energy, energy gap and vertical and adiabatic ionisation energy were analysed to find the suitable molecule for molecular wires.