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 with relevance to a variety of materials applications. Photochromes with long wavelength isomers (LW) capable of acting as photooxidants but with short wavelength isomers (SW) less capable of doing so are sought. This necessitates photochromes that revert only thermally and that have excited state reduction potentials that are more positive for LW than for SW. (As the difference in excitation energies is in the opposite direction, this requires a very large difference in ground state reduction potentials!)The parent perimidinespirohexadienone (PSHD) photochrome meets these basic requirements, but with a very modest difference in excited state reduction potential between SW and LW, thus with 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.

Differential photochromic v. electrochromic ring opening of quinazolinespirohexadienones

248th National Meeting (2014)

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