Dendron decorated chromophores for optical power limiting applications
Abstract: The need for protection of eyes and electro-optic sensors from powerful lasers has increased the need for new and better optical power limiting (OPL) materials that can protect against laser light. In this study the synthesis and characterization of dendron-coated OPL chromophores (porphyrins, thiophenes, and platinum(II) acetylides) are discussed. The work has been divided into two different main parts.In the first part it was investigated if dendrons could be attached to these chromophore molecules. The dendrons were attached using the versatile chemistry of the acetonide protected anhydride of 2,2-bis(methylol)propionic acid (bis-MPA). The resulting dendrimers were characterized with NMR, SEC and MALDI-TOF to verify that well-defined molecules were obtained.Well-defined virtually monodisperse dendron-coated chromophores up to the fourth generation were synthesized for the three different chromophores. For the porphyrins the fifth generation were also synthesized but molecular weight measurements showed that they were not perfect.In the second part the performance of the dendron-coated materials for protection against lasers was analyzed. Other spectroscopic studies such as absorption, emission, and lifetime measurements were also performed to understand the influence of the dendritic coating on the properties of the materials.The dendritic coating had little effect on the free-base porphyrins and the thiophenes and there were no differences in the OPL for different generations. The zinc-cored porphyrins showed significantly better OPL properties but their linear transmissions were low. The zinc porphyrins absorption and emission spectra were affected by the dendron coating and the OPL properties were deteriorated with increasing generation. The effects were most prominent for the largest dendrimers and it is believed that they change the conformation and vibrational substructure of the porphyrin. The platinum(II) acetylides were also influenced by the dendron coating. They showed improved OPL properties with increasing generation. This improvement is attributed to the longer lifetimes of the excited states for the larger dendrons, which increases the excited state absorption.Initial solid-state materials in a poly(methyl methacrylate) (PMMA) were made showing that the OPL effects are retained in the solid state but that the linear transmission and damage threshold are reduced.
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