Dendritic materials for optical applications: A. Synthesis and study of non-aggregating octasubstituted dendritic phthalocyanines for optical limiting applications B. Synthesis and study of two-photon dendritic dyes for biomedical imaging applications

Abstract

This dissertation investigates the synthesis and analysis of new dendritic compounds for their utility as nonlinear optical materials. Two-photon absorbing dendritic dyes and octasubstituted dendritic phthalocyanines utilize the dendrons along the periphery in order to shield the central, "active" core from the external environment. An attempt to obtain phthalocyanine materials for use as optical limiters entailed the attachment of dendritic substituents through a hydroquinone spacer to phthalonitriles which were then cyclized to give the target phthalocyanines. Investigation of the aggregation properties of these compounds showed that as the generation of the dendritic substituent increased, the amount of aggregation decreased. This was seen both in thin films as well as in solution. However, as the dielectric constant of the solvent increased, aggregation of individual phthalocyanines in solution also increased. Substitution on the periphery of the dendron also had a role in how the phthalocyanine behaved in solution. The presence of t-butyl groups in the meta positions along the periphery of the dendrimer further decreased the amount of aggregation that occurred in solution. The addition of zinc to the core of the phthalocyanine led to further prevention of aggregation, again in both thin films and in solution. Fluorescence studies on these compounds had indicated the presence of an energy transfer mechanism between the dendron periphery and the phthalocyanine core. The dendritic zinc phthalocyanines also displayed small KSV values which suggest that the approach of quenching molecules to the core of the phthalocyanine is greatly hindered in solution by the dendritic periphery. In the development of a material for biomedical imaging, a strong effect was exhibited by the change in polarity of the solvent on the two-photon absorption (TPA) of bis-styrylbenzene (BSB) dyes which resulted in a loss of the fluorescence quantum yield (phif) as the polarity increased. Covalent attachment of different generations of a 4-carboxy terminated dendron to the dye resulted in a smaller decrease in the phif based upon the generation of the attached dendron. A study of the solvent effect on the dicyano-substituted BSB dendritic TPA dye indicated the presence of a possible hydrogen bonding interaction between the dendron and the dye at low pH. This interaction resulted in a strong decrease in the phif of the dye, a loss that was partially remedied by raising the pH to 12.