Photophysical and Optical Limiting Properties of Axially Modified Phthalocyanines

As one of the most investigated organic compounds, phthalocyanines (Pcs) exhibit a stronger optical limiting response that can be used to protect human eyes, optical elements, and sensors from intense laser pulses, however, they tend to aggregate at high concentration. This aggregation usually adds relaxation pathways, shorten the excited state lifetime, and reduce the effective nonlinear absorption. A best strategy for reducing the intermolecular interactions between Pc molecules is to introduce more or less bulky axial substituents with which it would be expected to alter the electronic structure of the Pc compounds, to introduce a dipole moment perpendicular to the macrocycle, and to alter both intermolecular interactions as well as spatial relationships between neighboring molecules. As a result, a whole series of new highly soluble axially substituted MPc (M= In, Ga, Ti) compounds have been synthesized by us in recent years. Of interest is that their limiting response can be tailored over a very broad range due to the high architectural flexibility of the Pc structure. Future work will be focused on in-depth studies of the Pc–based solution and solid state systems to provide a detailed understanding of the factors affecting the optical limiting response.