Optimized synthesis and detailed NMR spectroscopic characterization of the 1,8a-dihydroazulene-1,1-dicarbonitrile photoswitch
Søren Lindbæk Broman, Sophie Lehn Brand, Christian Richard Parker,
Michael Åxman Petersen, Christian Gregers Tortzen, Anders Kadziola, Kristine Kilså,
and Mogens Brøndsted Nielsen*
Department of Chemistry, University of Copenhagen, Universitetsparken 5,
DK-2100 Copenhagen Ø, Denmark
E-mail: mbn@kiku.dk
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Abstract
An economical and effective protocol for large scale synthesis of the 2-phenyl-1,8a- dihydroazulene-1,1-dicarbonitrile (DHA) photoswitch has been developed. This compound is ring-opened by light to a vinylheptafulvene (VHF), which is thermally closed back to DHA. This compound serves as an important starting material for dihydroazulene photoswitches incorporating a substituent in the seven-membered ring and as a reference compound for comparison of properties. A detailed NMR spectroscopic characterization has allowed the assignment of all proton and carbon signals. In addition, the compound was characterized by X- ray crystallography. A correlation between the rate constant for thermal ring-closure of VHF to DHA and empirical parameters of solvent polarity (ET30) was established.
Keywords: Dihydroazulene, photoswitch, solvent polarity, thermoswitch, vinylheptafulvene
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Introduction
Molecular switches possess at least two reversible interconvertible states.1 A photochromic switch is a system where at least one of the conversions is light-induced.2 These systems are particularly interesting within the fields of molecular electronics, materials science, supramolecular chemistry, and biotechnology.3 Systems such as the azobenzene4 and the dithienylethene5 show great potential as future building blocks within molecular electronics. We have become interested in the dihydroazulene/vinylheptafulvene system (Scheme 1).6 DHA undergoes a light-induced ring-opening reaction to VHF that in turn undergoes a thermal ring- closure back to DHA.
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