Molecular DTE scaffolds with a phosphole ring at the backbone have been more recently explored by Yam et al. (14-27). Thieno[3,2-b]phosphole oxides (14-19) are photoswitchable using visible light, (i.e., UV radiation is not needed). The conjugated rings fused to a phosphole induce a reduction of the HOMO-LUMO gap without affecting the electron distribution substantially (Figure ). The FMOs are, once again, in agreement with our simple orbital rules, as in compounds 20-27 (Figures and).