Diaminoacenaphthylene, a Key But Elusive Intermediate toward Carbonyl-Substituted Perimidinespirohexadienone Photochromes
Dr. 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 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 perimidinespirehexadienone (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. Based on computationally predicted reduction potentials, carbonyl-substituted PSHDs are promising synthetic targets for increasing the difference in reduction potential between SW and LW and for making LW a far more potent photooxidant. Previous experimental results show that it is not possible to add carbonyls to the photochrome’s naphthalene “bottom” before coupling. Thus, it will be necessary to prepare an acenaphthylene-bottomed PSHD. This requires the synthesis of diaminoacenaphthylene. This seemingly simple molecule has proved very difficult to make. After ruling out the most straightforward syntheses and the use of protecting groups, we now detail our current synthetic routes toward this challenging intermediate.
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