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Synthesis

Light Triggers A Distant Bond Flip

Photoisomerization: Irradiating an N–H bond causes a conformational change at a methoxy group several bonds away

by Jyllian Kemsley
September 28, 2015 | APPEARED IN VOLUME 93, ISSUE 38

Ultraviolet and visible light are known to trigger isomerization in molecules, such as converting 11-cis-retinal to the all-trans form necessary for vision. Chemists have also studied systems in which targeting a hydroxyl O–H vibrational stretch with near-infrared light can change the conformation of the hydroxyl group or a neighboring group. A conformational switch may also be caused by targeting an N–H bond far from the isomerizing group, reports a team from the University of Coimbra, in Portugal (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b08588). Igor Reva and colleagues studied 6-methoxyindole, a bicyclic ring system that has –OCH3 and –NH– groups on different rings, separated by several bonds. In the syn conformer, the –OCH3 points toward the –NH– group. In the anti conformer, the –OCH3 points away from the –NH. The researchers found that by irradiating the molecules with near-IR laser light tuned to the frequency of the N–H stretch in either the syn or anti form, they could reversibly induce isomerization to the opposite form. This distant light-induced bond flipping could contribute to understanding certain sunlight-driven atmospheric reactions.

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