We previously reported two diarylethene compounds with quinoline and quinolinium backbones (39-40). The quinoline compound 39 shows the desired symmetric LUMO configuration and is photoreactive (Figure ). Finally, we explore a recently reported photoswitch in which excimeric emission in the open form is blocked upon photocyclization since the closed form does not favor the excimer structure. In Figure the FMOs involved in the bright S1 state are plotted. Interestingly, despite a contribution from the π-stacked pyrene units, the excited state is dominated by the suitable LUMO orbital that leads to photocyclization. Therefore, our rules are also able to predict the photoswitching activity of this compound.