Extending the π-conjugation of the peripheral diaryl units or at the backbone in order to lower the HOMO-LUMO energy gap of the open form is a known molecular design strategy to shift the excitation wavelength to the visible region. To model the impact of extending the π-conjugation on the photochemical properties of DTE chromophores, we consider the conjugation extension at the pendant side groups and at the backbone respectively using TfPh-CP-TfPh (Figure ) and T-Ph-T (Figure ) as models. To further explore the effect of the substituting units, we use a variable range of interaction energies (b parameter in the Hückel model) between pz orbitals of the additional atomic centers (X-labelled atoms in the two models). Diminishing the |b| value can be used as a simple way to simulate the decrease in the HOMO-LUMO gap of the conjugated substituents, as occurs with increasing conjugation length. Hückel model orbital energies predict the Ph substitution at the backbone (T-Ph-T) to induce a larger activation energy (larger HOMO-LUMO gap) than by increasing the conjugation in the side groups in TfPh-CP-TfPh. In both cases, there is a simultaneous destabilization of the HOMO and stabilization of the LUMO as |b| decreases (effective conjugation increases), resulting in a decrease in the HOMO-LUMO energy gap. Both models exhibit the same FMO symmetries as in hexatriene, that is, C2 antisymmetric HOMO and symmetric LUMO (Figure ). Notably, these symmetries are well preserved along the entire interaction range (-1 £ b £ 0), suggesting that the symmetry conditions derived from the WH rules for the conrotatory photoreaction remain unchanged. On the other hand, extension of the π-conjugation in the backbone or the side groups tends to localize the lowest excitation away from the six pro-cyclic carbon atoms, which is expected to eventually hinder the photoreactivity of the open form. In other words, we argue that overextending p-conjugation at the diaryl and/or backbone positions is expected to be detrimental to the quantum yield for photoreaction of the open chromophore.