Differential Photochromic v. Electrochromic Ring Opening of Quinazolinespirehexadi enenones
Drs. William Polik and Jason Gillmore
We are working to develop a new class of photooxidants based on organic photochromes that would add an additional level of gating to the process of photoinduced charge transfer (PICT) initiation of cation radical reactions. Photochromes with long wavelength isomers (LW) capable of acting as photooxidants but with short wavelength isomers (SW) less capable of doing so are sought. The parent perimidinespirehexadienone (PSHD) photochrome meet the basic requirements for such a system, but with a very modest difference in excited state reduction potential between SW and LW, thus minimal capacity for gating, and very modest photooxidizing power. Quinazolinespirohexadienones (QSHDs), PSHD analogs in which the naphthalene bottom has been replaced with a quinoline, are modestly more electron deficient and potentially more potent photooxidants. Our group has previously published QSHD synthesis and photochemistry, including the proof of direction of photochromic ring opening into the LW isomer. We have subsequently discovered that QSHD opens in the opposite direction upon one electron reduction to form a different electrochromic LW isomer. Computations of bond lengths, bond orders, and molecular orbitals help us rationalize these results.
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