Nakamura and Irie showed that the enthalpy difference between open and closed isomers in the ground state can be used as a simple computational criterion for determining the thermal stability of the closed form. Concretely, small DH, computed as DH = H(closed) -H(open), implies high stability of the closed isomer and vice versa. The thermal stability of the closed-ring isomer has been related to aromatic stabilization energy. Open chromophores with aromatic rings at the backbone are expected to present rather unstable closed forms due to the energy penalty required to break aromaticity. This is