46386-GB7
Design, Synthesis, and Photochromism Studies of Photo-Switchable Bispiropyran Polymers
The goal of this project was to develop the synthetic method and to understand fundamental properties of photo-switchable “smart” polymer systems that possess potential for site recognition of specific biomolecules and sensors of organic/inorganic compounds. Incorporation of unique shaped photochromic dye into polymers will enable construction of various self-assembly structures for new class of photo-responsive materials.
Spiropyrans are a class of photochromic compounds whose molecular structures are alterable upon exposure to UV/ visible light or changes in temperature. The typical reaction of spiropyran is the conversion between the non-polar Sp form with the polar MC forms. We are particularly interested in remarkable changes in polarity and structure (specifically, planarity) between Sp and MC forms. To effectively utilize these properties, we design a functional polymer having unique spiropyran “dimer” compound at the terminal. The polar face of the MC form dimer strongly attracts ionic species which can be released through visible light due to the transformation into the non-polar Sp form. The aggregates of the bispiropyran-polymer are more attractive since MC to Sp transformation destroys the planarity of the molecules, which will disallow the self-assembly structure of polymers. In this project, two models of bispiro compound-polymer conjugates are designed and synthesized. The self-assembly structures by phase separation of polymers and ionic interaction of bispiro MC forms will be studied using variety of techniques such as NMR, IR, AFM, TEM, and UV-vis. The fundamental photochromism study will disclose potential functions of novel bispiro polymer systems as “smart molecular machine”.
We have devoted to synthesize two different photochromic dimers, (1) 3,5-bis(1-(8-methoxy-1',3',3'-trimethylspiro[chromene-2,2'-indoline]-6-yl)-1H-1,2,3-triazol-4-yl)phenylmethanol (BIPSD) and (2) 3,5-bis(1,3,3-trimethylspiro[indoline-2,2’-phenanthrooxazine]-5-yl)ethynylbenzylalcohol (SPOD).
(1) BIPSD-polymer: Since the synthesis method of the first spiropyran dimer, BIPSD has been established and published previously in our group, we focused on the scale-up synthesis and polymer conjugation on this compound. Biodegradable amphiphilic triblock copolymer, poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide), PLLA-PEG-PLLA, was first synthesized, and the endgroups of the polymer was activated with p-nitrophenylchloroformate. The activated PLLA-PEG-PLLA was then reacted with BIPSD to yield BIPSD-PLLA-PEG-PLLA-BIPSD.
(2) SPO synthesis: The new spirooxazine dimer has been successfully prepared by multi-step synthesis route. The reactions include; Fisher Indol Formation from p-iodophenylhydrazine and 2-butanone, Sonogashira Coupling of iodoindole and 3,5-diethynylbenzylalcohol, and finally spiro-coupling reaction of the methylated indole dimer and 9-nitroso-10-phenanthrol. The Sonogashira reaction was a key to the entire synthesis scheme, and we optimized the reaction conditions and purification method. Silica gel column chromatography was generally used to purify the intermediates and the final product. Currently, this SPO is produced in large scale.
(3) Photochromism studies: Preliminary tests of photo reaction for BIPSD and its polymer systems have been performed using medium pressure mercury lamp and UV-vis spectroscopy. Visible light and heat treatments have also been examined and optimized for MC to Sp form conversion. To understand and improve the photochemistry of spiro-dimers for their effective use in binding/release of guest molecules or ions, our current efforts are focused on studying kinetics of thermal closure of spiropyran dimer in different solvents. The effect of polar and non-polar solvents and sample concentration has been investigated by monitoring UV-vis spectroscopy.
Plan for 09/2008-08/2009: In the second year of this project, we will focus on; 1) the preparation of polymer-spiro conjugates and their self-assembly structures, 2) analysis of assembled structures and their photoswitch effect, and 3) kinetic and binding studies upon UV/vis irradiation or temperature change. Two publications are currently planned for submission in 2008; “photochromism study on BIPSD-polymer conjugates” and “synthesis and characterization of novel spirooxazine dimer”. These results will be presented at; ACS Regional Meeting in Nashville, SERMACS, Nov 12-15 (1 oral and 2 posters); International Symposium on Stimuli-Responsive Materials at USM, ISSRM, Oct 28-30 (2 posters); and ACS National Meeting in Salt Lake City, Mar 2009 (not yet submitted).
Impact on PI and students: A graduate student, Davita Watkins has been supported by this PRF grant for her summer stipend. She completed her first graduate year with satisfactory academic grade and learning advanced organic synthesis skills through the research. Davita made a significant progress on this project. Two undergraduates are also involved in this project. They have worked during summer with university scholarships. A postdoctoral associate, Satish Kumar has just joined in our group supported by our department. He has extensive experience on photochromics synthesis and photochemistry. We expect the acceleration of this PRF project in the second year.
For the PI’s career development, this PRF support is significant. Since she has moved from Boise State University to the University of Memphis in 2007, to continue and achieve her research progress during laboratory start-up couldn’t have been smoothly done without the PRF fund. The potential seeds we are making by this grant will definitely become a big source for the large grants and publications.
