Light Triggers A Distant Bond Flip

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.