Ultrafast spectroscopy of a photoswitchable 30-amino acid de novo synthesized peptide

The ultrafast photoresponse of small, often cyclic peptides with azobenzene units has widely been investigated during the last years. Both the photoisomerization of the optical switch as well as the different conformational states of the peptide moiety can be characterized by optical spectroscopy. Here, we investigate the fast photoisomerization dynamics of an α-helical 30mer azobenzene peptide. The peptide is based on a construct used for the assembly of di-heme-binding maquettes. The femtosecond to picosecond photodynamics for the trans to cis isomerization of the optical switch was found to occur slower upon its insertion in the peptide construct. Both isomers are sufficiently photostable to allow spectroscopic analysis of conformational states, since the thermal cis-trans relaxation occurs over a period of several hours. This approach thus offers the possibility for the de novo design of photoresponsive chromopeptides which could be instrumental in unravelling fundamental dynamic features of assembly/disassembly triggered by fast photoswitches.