title: Aromaticity-Controlled Energy Storage Capacity of the Dihydroazulene-Vinylheptafulvene Photochromic System.
abstract: Photochemical conversion of molecules into high-energy isomers that, after a stimulus, return to the original isomer presents a closed-cycle of light-harvesting, energy storage, and release. One challenge is to achieve a sufficiently high energy storage capacity. Here, we present efforts to tune the dihydroazulene/vinylheptafulvene (DHA/VHF) couple through loss/gain of aromaticity. Two derivatives were prepared, one with aromatic stabilization of DHA and the second of VHF. The consequences for the switching properties were elucidated. For the first type, sigmatropic rearrangements of DHA occurred upon irradiation. Formation of a VHF complex could be induced by a Lewis acid, but addition of H2 O resulted in immediate regeneration of DHA. For the second type, the VHF was too stable to convert into DHA. Calculations support the results and provide new targets. We predict that by removing one of the two CN groups at C-1 of the aromatic DHA, the heat storage capacity will be further increased, as will the life-time of the VHF. Calculations also reveal that a CN group at the fulvene ring retards the back-reaction, and we show synthetically that it can be introduced regioselectively.
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
authors.forename: Anders B
authors.initials: AB
authors.lastname: Skov
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark. slb@kiku.dk.
authors.forename: Søren Lindbaek
authors.initials: SL
authors.lastname: Broman
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
authors.forename: Anders S
authors.initials: AS
authors.lastname: Gertsen
authors.affiliation: University of Helsinki, Department of Physics, Gustaf Hällströmin katu 2a, 00014, Helsinki, Finland. jonas.elm@helsinki.fi.
authors.forename: Jonas
authors.initials: J
authors.lastname: Elm
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
authors.forename: Martyn
authors.initials: M
authors.lastname: Jevric
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.|University of Florence, Department of Chemistry, Via della Lastruccia 3-13, 50019, Sesto Fiorentino (FI), Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Cacciarini
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Kadziola
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark. kmi@chem.ku.dk.
authors.forename: Kurt V
authors.initials: KV
authors.lastname: Mikkelsen
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark. mbn@chem.ku.dk.
authors.forename: Mogens Brøndsted
authors.initials: MB
authors.lastname: Nielsen
keywords: electrocyclic reactions; energy conversion; molecular devices; photochromism; renewable resources