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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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