Multimode Photoswitches Incorporating Dihydroazulene

The dihydroazulene/vinylheptafulvene (DHA/VHF) system is a photo-/thermo-switch couple that has found interest for MOST applications. Structure–property relationships have been established for tuning optical and isomerization properties of this pair as well as the energy difference between the two isomers. To expand the intrinsic features and increase the amount of information that can be stored within a single molecule, DHA units have been incorporated into multimode photoswitches, constituted either by two or more DHAs (homomer-type multiphotoswitch) or by DHAs connected to other photochromes, such as azobenzene, dithienylethene, norbornadiene, spiropyran and tetraethynylethene (heteromer-type multiphotoswitch). When connected by the right spacer, the properties of these complex frameworks may be different from just the sum of the properties of the individual units, which may lead to better light-harvesting behavior, energy storage capacities, and control of storage times. This chapter reviews work on multimode photoswitches incorporating at least one DHA photochromic unit and describes the property control in relation to the multiphotoswitch architecture.