The spectroscopy and dynamics of a novel hemithioindigo-based photoswitch forming a omega-amino acid derivative are presented. Light absorption in the visible spectral range induces photoisomerization between Z and E configurations with quantum yields in the 10% range. The Z isomer is thermally stable, while the E isomer relaxes back to the Z form within several hours. The E isomers provides a distinct spectral range, where the photoisomerization process can be initiated selectively. Both directions of the photoisomerization are investigated by transient absorption spectroscopy and time constants for the formation of the photoproduct in the 10-30 ps range are observed. The ability of the hemithioindigo-based photoswitch to drive structural dynamics in peptides and proteins is tested for two omega-amino acid derivatives forming linear and cyclic structures. (c) 2006 Elsevier B.V. All rights reserved.