Polyyne-metal complexes for use in molecular wire applications: A DFT insight

Abstract Metal complexes of the form C5H5N -[C N]-X-[C C]n- C5H5N, where X = Ag, Au, Co, Cu and n = 1,2,3 are studied by Density Functional Theory (DFT) methods to analyze their structural and conducting properties. Relative singlet and triplet energies, Bond length alternation (BLA), transport barrier, molecular orbitals, absorption spectrum, charge transfer with metal surface, charge modified geometry and reorganization energies of these metal complexes are analyzed. It is found that BLA values did not vary significantly in pyridine terminated metal complexes compared to pyridine terminated polyynes, however significant increase in HOMO (highest occupied molecular orbital) energies were noted, which also resulted in lower transport barriers. HOMO-LUMO (lowest unoccupied molecular orbital) energy gaps are also reduced notably to 2.52–3.11 eV which is much lesser than previously reported polyyne chains. Larger reduction in BLA was observed for positively charged polyyne-metal complexes compared to negatively charged ones.