Multistate Photoswitches: Macrocyclic Dihydroazulene/Azobenzene Conjugates

Abstract

Molecules comprised of three covalently linked bi-stable switches can exist in states described by a combination of binary numbers, one for each individual switch: ⟨000⟩, ⟨001⟩, etc. Here we have linked three photo-/thermoswitches together in a rigid macrocyclic structure, one azobenzene (bit no 1) and two dihydroazulenes (DHAs; bits no 2 and 3) and demonstrate how electronic interactions and unfavorable strain in some states can be used to control the speed by which a certain state is reached. More specifically, upon irradiation of state ⟨000⟩, the AZB isomerizes from trans to cis and the two DHAs to vinylheptafulvenes (VHFs), generating ⟨111⟩. The thermal VHF-to-DHA back-reactions from this state also occur stepwise and can be accelerated by photo-induced AZB cis-to-trans conversion, proceeding via ⟨011⟩ to ultimately furnish ⟨000⟩. Overall, the accessibility to a specific state of one bit was found to depend on the states of its neighboring bits.

Keywords: azo compounds; electrocyclic reactions; isomerization; macrocycles; photochromism.