Synthesis, characterization and photophysical studies of poly(aryl ether) monodendrons and pyrene-labeled poly(aryl ether) monodendrons.

摘要

Poly(aryl ether) dendrimers are one of many types of dendrimers currently being synthesized and studied. Poly(aryl ether) monodendrons are good models for studying the microscopic structure and dynamics of dendritic compounds. Photophysical studies can be performed by attaching a chromophore to the monodendron, or they can be studied by themselves. The data collected from these studies can be used to evaluate the theoretical models proposed for dendrimer structure. The results also help determine certain physical properties of these molecules, such as size, solvation, and permeability as a function of dendrimer size (generation) and solvent.;The intent of this project was to synthesize a series of poly(aryl ether) monodendrons, characterize them, attach a photophysical probe and study their photophysical properties. These studies will attempt to test the applicability of various theoretical models to these materials. The monodendrons were synthesized using methyl-3,5-dihydroxybenzoate (1) as the monomer in a modification of Frechet's synthesis based on 3,5-dihydroxybenzyl alcohol (Hawker, C. J.; Frechet, J. M. J. J. Am. Chem. Soc. 1990, 112, 7638-7647.). The monodendrons were then labeled with a pyrene moiety at the core. The pyrene was attached to the monodendrons by coupling the bromide terminated poly(aryl ether) monodendrons with 1-hydroxypyrene.;The compounds were then characterized by ;The pyrene labeled monodendrons photophysical properties were also studied. The spectra and lifetimes of these compounds differed from those of pyrene. The spectra were simpler and the lifetimes significantly shorter, and both were found to be insensitive to solvent. To study the ability of the monodendron to protect the pyrene focus, an oxygen quenching study was performed. A model determining the surface area that should be shielded was evaluated and the diffusion of oxygen calculated. The monodendrons were observed to shield the pyrene focus, reducing the ability of oxygen to quench it.;These studies lead one to believe that the monodendrons can back-fold and that they can effectively encapsulate a moiety at the focus. The lower generations have a more open structure than the higher generations. As the size increases, the permeability decreases. This results in a model that describes dendrimers as not completely extended nor fully back-folded, which agrees with the newer treatment of dendrimers in solution.