Detailed electronic, structural, photophysical, and redox studies of a series of meso-pentafluorophenyl-substituted hexaphyrins, namely amethyrin (1), rosarin (2), and rubyrin (3), are described. In prior work, it was found that the electronic states of the antiaromatic hexapyrrolic macrocycle, rosarin 2, could be modified by exposure to several Brønsted acids (e.g., HCl, HBr and HI) to produce either one- and two-electron reduced species, or both. In an effort to gain further insights into the reactivity of hexaphyrins possessing different π-conjugation pathways, the β-dodecamethyl-substituted amethyrin 1 was prepared and its electronic structure was analyzed along with that of the o-phenylene-bridged rubyrin 3 and rosarin 2 The [4n] and [4n+2] π-conjugated formulations of 2 and 3, respectively, were inferred from steady-state, fs-transient absorption and two photon absorption measurements. Similar photophysical analyses lead to the conclusion that 1 is best considered as nonaromatic or weakly antiaromatic. Magnetic circular dichroism (MCD) spectroscopic analyses of hexaphyrins 1 and 3, as well as comparisons to 2, and theoretical perimeter MO diagram analyses provided support for the electronic assignments. In contrast to what was found for 2, simple protonation of 1 and 3 by halohydric acids did not induce an evident, redox-based change in the electronic structure of the macrocycle.
Bibliographical noteFunding Information:
Support is acknowledged from the U.S. National Science Foundation (CHE-1402004 to J.L.S.), the Robert A. Welch Foundation (chair funds to J.L.S.), the Japan Society for the Promotion of Science (JSPS: No. 16K05700 and 17H05377 to M.I. and No. JP15H02172 and JP15H009 to N.K.), a bilateral program between JSPS and the National Research Foundation (NRF) of South Africa to N.K., the Global Research Laboratory (2013K1A1A202050183 to D.K.) and the Basic Science Research Program (2015R1A2A1A10052586 to C.H.L.) administered through the National Research Foundation of Korea (NRF) and funded by the Ministry of Science, ICT (Information and Communication Technologies) and Future Planning.
All Science Journal Classification (ASJC) codes
- Organic Chemistry