At 0 and 180 , the ⇡-orbitals have a rectilinear shape as the two ⇡-orbital systems in the molecule are separated due to the D 2h -symmetry and the MO results from contributions from only one of the ⇡-systems. Starting from 0 , as the dihedral angle between the endgroups increases the HOMO-LUMO gap narrows and at 90 the HOMO and LUMO become degenerate and cross. With increasing dihedral angle, we again see an increase in the helicality of the HOMO that saturates close to 90 and then decreases again with a further increase towards 180 . There is a notable difference from the diphenyl-diyne. The helicality increases quickly with twist, reaching a MAD < 10 already at a 20 dihedral angle then slowly decreases to a minimum MAD of 4. Thus the HOMO becomes an almost perfect helix much like the odd-carbon cumulene.