Testing Quinazolinespirohexadienone Photochromes As Gatable Photoinduced Charge Transfer Initiators
Dr. Jason Gillmore
The quinazolinespirohexadienone (QSHD) photochromes have the potential to gate photoinduced charge transfer (PICT). The long wavelength isomer, LW, is a modest photooxidant while the short wavelength isomer, SW, is not able to act as a photooxidant. SW isomerizes to LW by absorbing UV light. LW is capable of initiating PICT from a donor molecule after excitation by visible light. The cation radical of the donor molecule can then be used in a cation radical chain process. It is important that the fade from LW to SW occurs by a purely thermal mechanism so that the LW photochemical channel is available for PICT. Photochrome reversion from LW to SW has been studied for the parent photochrome, perimidinespirohexadienone (PSHD), and QHSD in the dark and with irradiation at 578 nm. After accounting for temperature differences between the solutions, it appears that PSHD LW reversion is a purely thermal process. QSHD photochrome LW reversion shows very modest acceleration by 578 nm light, but this may not be statistically significant. While the QSHD LW is not a particularly potent photooxidant, it should be sufficient to oxidize N,3-(bis-trans-1-propenyl)carbazole. This readily oxidizable monomer is distinctive because upon one electron oxidation it undergoes a genuine cation radical polymerization. Syntheses of this monomer and close analogs are underway with the ultimate goal of testing QSHD’s ability to gate the PICT-initiated cation radical polymerization of these monomers.
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