Ricerc@Sapienza

tThe control of the transmission of the energy transported by optical waves is of extreme importance forthe realization of those advanced technologies which require high speed of operation and fast switching.Such a task can be approached through the design and preparation of materials that possess modulableoptical properties. In the present review the aspect of material science behind the realization of the effectof optical limiting, OL (or optical power limiting, OPL), will be considered focusing on those materialsbased on conjugated metallo-macrocycles like porphyrins, phthalocyanines and derivatives. The choiceof these molecular materials for OL purposes is motivated by the fact that the optical properties of suchannulated systems can be finely modulated in a controlled fashion by changing the chemical structure ofthe complex. These changes involve the variation of the central metal, the extent of electronic conjugationof the ring, the nature and the number of peripheral ligands, and the eventual introduction of axial ligandscoordinated by a central metals with a valence higher than +2. An attempt will be made to establishrelationships between the structure of the macrocyclic complex and the relative OL properties takinginto account the most recent developments in the field. During this analysis we will also discuss theaspect of optically passivity, i.e. the characteristic of the OL materials of undergoing fast changes ofoptical properties according to an internal mechanism of self-activation.