Graduate student Marco Messina (advised by Maynard & Spokoyny) & postdoc Jon Axtell (Spokoyny group) led the team whose research was featured.
The paper titled “Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants” was published in the May 17, 2016, issue of the Journal of the American Chemical Society (JACS). It was highlighted in the June 17, 2016 issue of Science Magazine.
Typically, chemists utilize either metal-based complexes or organic dyes to harness energy from visible light thereby enabling chemical transformations in either small molecules or in the formation of polymers. Until this work, the use of boron-rich clusters to promote chemical transformations using visible-light had not been realized. Research by Messina, Axtell and co-workers depicts the discovery that air-stable perfunctionalized icosahedral dodecaborate clusters of the type B12(OCH2Ar)12 (Ar = Ph or C6F5) can act as a new class of metal-free photo-initiators in the polymerization of a wide array of styrene monomers bearing electron-withdrawing and electron-donating substituents.
Research team leaders graduate student Marco Messina and postdoc Dr. Jon Axtell.
The UCLA team was able to show the first example of metal-free, visible light induced initiation and subsequent cationic polymerization of the unactivated olefin isobutylene—a monomer typically polymerized using environmentally harsh conditions such as strong acids or metals. The boron-rich clusters utilized in this work are stable in ambient conditions and can be readily functionalized with a variety of functional groups – thereby tuning their redox potentials.
Photophysical studies conducted in a collaboration with a Caltech group at the Beckman Institute showed an excited-state reduction potential of 2.98 V (vs. SCE) for the B12(OCH2C6F5)12 cluster—the strongest reported visible light induced excited-state reduction potential of a molecular system to date. In collaboration with Yiqun Wang (Alexandrova group), the team also investigated electron excitation pathways within the boron-rich cluster via time dependent density functional theory (TD-DFT) studies. Ongoing work is now focused on elucidating the mechanism for polymerization, investigating methods to control the polymerizations, and investigating the photo-physical properties of other B12-based cluster derivatives.
Other UCLA team members were undergraduate summer researcher Yiqun Wang (Alexandrova group), undergraduate researcher Paul Chong (Spokoyny group), graduate students Alex Wixtrom & Kent Kirlikovali (Spokoyny group), Dr. Brianna M. Upton (Kasko group, UCLA Bioengineering) and UCLA’s Molecular Instrumentation Center (MIC) X-Ray Diffraction Staff Scientist Dr. Saeed Khan. Team members from Caltech’s Beckman Institute include Bryan Hunter, Dr. Oliver Shafaat, Dr. Jay Winkler, and Prof. Harry Gray.
Photo by Penny Jennings/UCLA Department of Chemistry and Biochemistry