The effect of chemical substitutions On the energetical landscape of an optical molecular switch (Phys. Client Chem. Phys. 2008, 10, 1243) was studied with the aid of ab initio electronic structure methods. Series of different chemical moieties were substituted into the molecular frame of 7-hydroxyquinoline as well as into the "molecular crane" at position 8 of the frame It was shown that the pi-electron-donating/withdawing properties of substituents substantially modify the energetical landscape of the system in the ground as well as in the lowest excited pi pi* and n pi* singlet states