Aggregation effects in non-linear absorption of CuPc–SiO2 sono-xerogels

It is known that aggregation effects in metallophthalocyanine/SiO2 composites play an important role in the optical properties of these materials. With the aim to avoid phthalocyanine dimer and oligomer formation induced in aqueous solution, alternative processing methods for trapping the organic in the matrices have been tested. The combination of ultrasonic energy used to promote the reactions and the methanol used as solvent, makes it possible to obtain monolithic xerogels under extremely acid conditions, preserving their homogeneity and transparency. Textural parameters and pore size distribution of the composites and the optical absorption features have been evaluated. Finally, the effects of molecular self-association degree on the non-linear absorption of the samples have been analyzed. All the samples studied exhibit reverse saturable absorption behavior but the figure of merit is strongly determined by the aggregation state of the active phase in the composite.