A diarylethene with two nitronyl nitroxides: Photoswitching of intramolecular magnetic interaction

A diarylethene having two nitronyl nitroxides, 1,2-bis[6-(1-oxyl-3-oxide-4,3,5,5-tetramethylimidazolin-2-yl) -2-methyl-1-benzothiophen-3-yl]hexafluorocyclopentene (2a), was synthesized in an attempt to control the intramolecular magnetic interaction by photoirradiation. The photochemical conversions from open-ring isomer 2a to closed-ring isomer 2b and from 2b to 2a were both almost 100%. Magnetic measurement revealed the antiferromagnetic interaction between two nitronyl nitroxides remarkably increased from 2J/k(B) = -2.2 K to 2J/k(B) = -11.6 K when the diarylethene spin coupler was switched from the open-ring isomer 2a to the closed-ring isomer 2b. ESR measurements were also carried out for both 2a and 2b in benzene solutions at room temperature and in MTHF solid solutions at cryogenic temperature. Both ESR and magnetic measurement indicated that the intramolecular interaction was switched by the photochromic spin coupler.