The degenerate frontier orbitals of cumulenes with even number of double bonds (odd no. of carbon atoms) can be described as helical. Upon reduction of the molecular symmetry in these cumulenes, the orbitals split into quasi-degenerate pairs of P and M helices. a,w-disubstitution reduces the symmetry from D2d to C2 and makes the symmetry-adapted molecular orbitals explicitly helical. We present a strategy for breaking the quasi-degeneracy of the orbitals by using substituents. Due to the symmetry of the helical orbitals, coherent electron transport is predicted to be very low when the orbitals are quasi-degenerate as there will be destructive interference between the orbital pairs of opposite helicity. Through density functional theory and non-equilibrium Green’s functions calculations we predict a difference of almost two orders of magnitude in the transmission depending on the substituent pattern. These results outline a strategy for designing cumulene-based devices where the coherent transport is predominantly through helical orbitals of the same helicity.

Utilizing the helical frontier orbitals of cumulenes in molecular electronics

255th National Meeting (2018)

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