and the difference in activity between E/Z 1 (25-fold), it must be noted that in the case of the cyclic azobenzene derivatives, the ligand can be switched reversibly under the experimental conditions (by alternative irradiation with blue and green visible light) whilst the stilbene derivatives both photofragment under UV-light (λ = 405 nm) leading to an irreversible process. Thus the azobenzene scaffold represents a significant improvement over the first generation scaffold.