Exploring New Routes toward Carbonyl-substituted Perimidinespirohexadienone Photochromes as Potential Photochromic Photooxidants

Photoinduced charge transfer (PICT) is a useful means of generating organic ion radicals. Cation radicals generated by PICT have relevance in a variety of applications of materials science interest, including new approaches to volume holographic data storage and 3D microfabrication. However a limitation to the use of PICT-initiated cation radical reactions is the persistence of photooxidant in the material subsequent to completion of the desired reaction. For instance, in data storage, this prohibits the use of the writing laser to read out the data without a “fixing” step that may alter the material. We are therefore attempting to develop a reversible pro-photooxidant system to gate sensitivity to PICT, in essence only having a photooxidant present when it is desired. Organic photochromes have long been used to “gate” optical properties, specifically color (absorbance) – in essence Transitions® lenses “gate” the presence of sunglasses. The increase in conjugation that underlies the change in absorbance upon isomerization of a photochrome also has significant impact on electronic properties. This phenomenon has received much less attention. In keeping with our group\u27s ongoing development1 of the perimidinespirohexadienone (PSHD) family of photochromes as potential photochromic photooxidants , in which one isomer is a good photooxidant, while the other isomer is not, we have explored a variety of routes to PSHDs bearing carbonyl substituents, which calculations2 predict to our most potent photochromic photooxidant candidates yet. Mechanistic lessons learned from several failed synthetic routes will be described, along with our current approaches in which the carbonyls are to be installed after coupling to form an initial photochrome without carbonyl substituents. References: (1) Moerdyk, J.P.; Speelman, A.L.; Kuper, K.E.; Heiberger, B.R.; Ter Louw, R.P.; Zeller, D.J.; Radler, A.J.; Gillmore, J.G. Synthesis and photochemistry of two quinoline analogs of the perimidine-spirohexadienone family of photochromes. J. Photochem. Photobiol. A 2009, 205, 84-92. (2) Speelman, A.L.; Gillmore, J.G. Efficient Computational Methods for Accurately Predicting Reduction Potentials of Organic Molecules. J. Phys. Chem. A 2008, 112 (25), 5684-5690. This material is based upon work supported by the National Science Foundation under grants CHE-0952768 (CAREER), CHE-0629174 (URC), and DUE-0728574 (S-STEM)