Reversible Photoredox Switching of Porphyrin-Bridged Bis-2,6-di-tert-butylphenols

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• 作者：Shinsuke Ishihara ; Jonathan P. Hill ; Atsuomi Shundo ; Gary J. Richards ; Jan Labuta ; Kei Ohkubo ; Shunichi Fukuzumi ; Akira Sato ; Mark R. J. Elsegood ; Simon J. Teat ; Katsuhiko Ariga
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：October 12, 2011
• 年：2011
• 卷：133
• 期：40
• 页码：16119-16126
• 全文大小：1037K
• 年卷期：v.133,no.40(October 12, 2011)
• ISSN：1520-5126

文摘

Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV鈥搗is spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions. Conversely, photoreduction occurs in the presence of a sacrificial electron donor. Transient absorption spectroscopy and electron spin resonance spectroscopy were applied to investigate the processes in photochemical reaction, and radical intermediates were characterized. That is, photooxidation initially results in a phenol-substituent-centered radical, while the reduction process occurs via a delocalized radical state involving both the macrocycle and 5,15-substituents. Forward and reverse photochemical processes are governed by different chemical mechanisms, giving the important benefit that conversion reactions are completely isolated, leading to better separation of the end states. Furthermore, energy diagrams based on electrochemical analyses (cyclic voltammetry) were used to account for the processes occurring during the photochemical reactions. Our molecular design indicates a simple and versatile method for producing photoredox macrocyclic compounds, which should lead to a new class of advanced functional materials suitable for application in molecular devices and machines.