Axial torsion of allene reduces its symmetry to D 2 and splits the helical MO pairs as the helix either unwinds and become more bonding (lower eigenvalue), or overwinds and becomes more antibonding (higher eigenvalue). Consequently, the two helical components of the transition do not contribute equally when the dihedral angle is changed from 90 o , and the transitions become optically active. This is demonstrated in Figure , where the end-group orientation of allene is changed, and the energies of the two B 1 excited states change accordingly. As the opposing helical components are emphasized in each transition, the rotatory strength increases systematically with differing sign for both transitions. The 2B 1 state becomes more active as it is the one that is electric dipole allowed at 90 o . Torsion of allene is realized in a series of cyclically alkylsubstituted allenes, where the alkyl linker constrains the structure. These have been synthesized and studied for their helical MOs in other contexts. The series of cycloallenes have a perturbed structure where both the allenic bond angle and dihedral angle are distorted. The frontier MOs and electronic transitions of allene are retained in the cycloallenes at the same torsion angle (ESI Figure ). As the helical MOs are split energetically they do not contribute equally to the electronic transitions, and consequently the cycloallenes have improved chiroptical response at more acute torsion angles (Fig. ). This exemplifies how the energetic tuning of the helical frontier MOs of allene can be used to optimize its optical activity.