In an attempt to exploit the large geometry changes associated with azobenzene photo-isomerization for the modulation of antibody-antigen interaction, we introduced in the backbone of the FLAG peptide (DYKDDDDK), an azobenzene unit to photo-modulate its conformational states and consequently its interaction with the monoclonal anti-FLAG-tag antibody M1. The FLAG-tag system is an established technique for purifying and detecting the corresponding fusion proteins. In this context, conflicting evidence has been presented regarding the necessity of calcium for stable binding. Using surface plasmon resonance, we showed that not the initial recognition but certainly the stability of the complex improves in the presence of calcium. Subsequently, we substituted two or three of the central aspartate residues for an artificial, azobenzene-based, photo-responsive amino acid. Four structural isomers of the artificial amino acid were considered, in total twelve FLAG-tag analogues were synthesized. Two showed significant differences in their ability to bind to the antibody in their cis versus their trans state. Interestingly, these two peptides are the two shortest of the twelve photo-peptides investigated. Finally, it was shown that for these two FLAG-analogues switching between cis and trans states is possible in the presence of the antibody.