Amine terminated polyynes as candidates for molecular wire applications: A DFT study

Abstract

The structural and conducting properties of four amine terminated polyynes CAN[n],PHN[n],NCH3[n] and NH2[n], with n = 2,4,6,8 are studied at density functional theory (DFT) level, and compared with two non-amine terminated cases(BT[n] and PY[n]) whose high single molecule conductance was reported experimentally. Helical molecular orbitals delocalized over the whole molecule are observed for amine terminated polyynes which will improve the conductance. The amine terminated polyynes possess high HOMO energy, hence lesser transport barrier, along with reduced bond length alternation (BLA) values. The reduction in BLA of amine terminated polyynes is also confirmed by the shift of the collective CC stretching frequency to lower values. A significant reduction in BLA is noted followed by a transfer of negative charge to the molecule as shown by the BLA of the anions. Also electron reorganization energies are much reduced for CAN [2], CAN [4] and PHN [2] terminated polyynes. In this way the conducting properties of the polyynes are enhanced for amine terminated polyynes.