Design and synthesis of dendrimers for studying two-photon absorption characteristics
Sims, Michael Keith
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While entering a technologically advanced world, where inventions of weapons occur rapidly, there is a constant need for research leading up to and preventing these weapons from being harmful. The use of lasers as an eye-damaging agent is one such weapon that requires the construction of good optical limiting materials that combat the harmful effects of these lasers. Optical power limiting materials should have the capability to respond quickly as well as span a large frequency range. Over the last two years, research has been conducted on the synthesis and absorption characteristics of new dendrimers incorporating from 3-6 chromophores that are capable of optical limiting of laser pulses in the visible region (400-600 nm) of the spectrum. These chromophores have been coupled to two new core molecules based on thiophosphoryl and cyclophosphazene derivatives by Wittig methodology yielding G-0 dendrimers with high chromophore density.The chromophores incorporated in these dendrimers are capable of providing laser protection by two-photon and reverse saturable absorption from highly absorbing excited states. The excited state absorption can be modeled by SbCl5 oxidative doping, forming stable bipolaronic dications in solution. Convergent approach to dendrimer synthesis was utilized in the preparation of the compounds constructed. In order to obtain absorption characteristics for these compounds, an initial doping with SbCl5 was mandatory. The formation of a bipolaron dication in solution resulted in large absorbances between 400 nm and 800 nm. Studies of optical limiting capabilities by way of two-photon absorption are currently underway, based on the generation of similar photogenerated bipolaronic states.