title: Reversible photoredox switching of porphyrin-bridged bis-2,6-di-tert-butylphenols.
abstract: 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-vis 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.
authors.affiliation: WPI Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Ishihara
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Hill
authors.forename: Atsuomi
authors.initials: A
authors.lastname: Shundo
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Richards
authors.forename: Jan
authors.initials: J
authors.lastname: Labuta
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Akira
authors.initials: A
authors.lastname: Sato
authors.forename: Mark R J
authors.initials: MR
authors.lastname: Elsegood
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ariga
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D055668:Photochemical Processes; D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010636:Phenols; D011166:Porphyrins; C035407:2,6-di-tert-butylphenol