title: Synthesis and redox and photophysical properties of benzodifuran-spiropyran ensembles.
abstract: Two benzodifuran (BDF)-coupled spiropyran (SP) systems and their BDF reference compounds were obtained in good yields through Huisgen-Meldal-Sharpless "click" chemistry and then subjected to investigation of their electrochemical and photophysical properties. In both SP and merocyanine (MC) forms of the coupled molecules, the BDF-based emission is quenched to around 1 % of the quantum yield of emission from the BDF reference compounds. Based on electrochemical data, this quenching is attributed to oxidative electron-transfer quenching. Irradiation at 366 nm results in ring opening to the MC forms of the BDF-coupled SP compounds and the SP reference compound with a quantum efficiency of about 50 %. The rate constants for the thermal ring closing are approximately 3.4×10(-3)  s(-1). However, in the photostationary states the MC fractions of the coupled molecules are substantially lower than that of the reference SP compound, attributed to the observed acceleration of the ring-closing reaction upon irradiation. As irradiation at 366 nm invariably also excites higher-energy transitions of the BDF units in the coupled compounds, the ring-opening reaction is accelerated relative to the SP reference, which results in lower MC fractions in the photostationary state. Reversible photochromism of these BDF-coupled SP compounds renders them promising in the field of molecular switches.
authors.affiliation: Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, 3012 Bern, Switzerland.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Jie
authors.initials: J
authors.lastname: Ding
authors.forename: Songjie
authors.initials: S
authors.lastname: Chen
authors.forename: Christoph
authors.initials: C
authors.lastname: Beyer
authors.forename: Shi-Xia
authors.initials: SX
authors.lastname: Liu
authors.forename: Hans-Achim
authors.initials: HA
authors.lastname: Wagenknecht
authors.forename: Andreas
authors.initials: A
authors.lastname: Hauser
authors.forename: Silvio
authors.initials: S
authors.lastname: Decurtins
mesh_terms: D001572:Benzofurans / Q000737:chemistry*; D001578:Benzopyrans / Q000138:chemical synthesis* / Q000737:chemistry; D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis* / Q000737:chemistry; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D009574:Nitro Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D013141:Spiro Compounds / Q000737:chemistry*
chemical_list: D001572:Benzofurans; D001578:Benzopyrans; D006576:Heterocyclic Compounds, 4 or More Rings; D007211:Indoles; D009574:Nitro Compounds; D013141:Spiro Compounds; C548873:merocyanine; C088184:spiropyran