Overall, our results show that simple inspection of the FMOs (HOMO and LUMO), that is spatial localization and the bonding or antibonding character, is an excellent approach to predict the photoswitching activity of DTEs and can be used to design new compounds with the desired capabilities. These simple guidelines are based on the WH rules, but go beyond them, since they deduce the applicability of the WH rules in a more general family of chromophores: substituted molecules based on the DTE scaffold. Moreover, the few examples that defy the rules can be rationalized due to the breakdown of the one-electron approach, that is, the characterization of the excited state (only) in terms of the HOMO and LUMO. In those cases, we provide a more complete and still simple (many-electron) approach based on the calculation of electronic states (instead of molecular orbitals), which is able to overcome these limitations. Moreover, we have rationalized the thermal stability of DTE derivatives in the closed form. The computed open/closed ground state energy differences provide a guide to the relative stability of the closed form with respect to the open structure, which can be related to the aromaticity of the latter. Although our study has focused, for the most part, on the characterization of the photocyclization capabilities of DTE derivatives, the rules derived from our investigations are general enough to apply to other DAEs.