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Gillmore Research Group – Organic Photochemistry

Photochromic Photooxidants:
a new application of old photocromes,
toward gating photoinduced charge transfer

There is an opportunity to join a thriving organic photochemistry research group at Hope College, with a primary focus on incorporating undergraduate students into all aspects of the research endeavor. In the process these student collaborators gain familiarity with organic synthesis, photochemistry, electrochemistry, ion radical intermediates, polymers, and materials research. Together, we develop gateable photosensitizers for photoinduced charge transfer (PICT) based on a family of photochromic compounds.

Photochromic organic molecules are compounds that undergo a reversible photochemical rearrangement from a short wavelength (SW) form to a long wavelength (LW) form, with reversion occurring thermally, photochemically, or both. The vast majority of organic photochromes have been investigated for applications in ophthalmic lenses (e.g., Transitions® lenses), novelty items, or data storage applications all related to their color change. Studies of the spectral changes, molar absorptivity, reversibility, and fatigue resistance predominate. Exploration of other dynamic properties of photochromic compounds has been far more limited. Extremely little is known regarding the redox properties of these compounds. Very few ground state redox potentials have been measured, and it appears that not a single excited state reduction or oxidation potential has been explicitly reported. In many cases, the structural changes that underlie the photochromic transformation are profound and likely to significantly alter the redox properties of the molecules in question.

In the Gillmore Research Group at Hope College, photochromes from the perimidinespirocyclohexadienone family are being prepared and studied as potential "photochromic photooxidants." Students are synthesizing known and novel compounds in this family of compounds. Students also do all the characterization of structure, photophysical properties, and ground and excited state electrochemical properties, using NMR, UV-Vis, Cyclic Voltammetry, and other techniques. Newly acquired instrumentation in the group and in the department will allow us to better explore unique structures and differential photochromic vs. electrochromic rearrangement.

A variety of structures within the same broad family of photochromes are being and will continue to be synthesized by multiple students in an attempt to tune these properties in a rational manner. Eventually it is hoped that a library or ladder of potential photochromic photooxidants can be developed. These photochromic photooxidants will ultimately allow sensitivity towards chemical initiation by PICT to be switched on and off. There are several followup cation radical processes of great interest to materials science (polymerization, 3D microlithography, holographic data storage, waveguides) that it would be interesting or advantageous to gate. As gateable photooxidants are developed they will also eventually be tested in these real applications, or in model reactions thereof.

The Gillmore group also has begun to develop computational methods to allow accurate and efficient prediction of redox properties to guide us to the most promising next generation of synthetic targets.

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