The Syk protein plays an important role in immune receptor signaling. The Syk tandem SH2 domain (tSH2)-ITAM interaction is important for recruiting Syk to the receptor complex and for Syk kinase activation. A peptidomimetic ligand for tSH2 was synthesized in which a photoswitchable azobenzene moiety was incorporated. Such a photoswitchable moiety may regulate the distance between the two phosphotyrosine containing ITAM sequences, which bind to tSH2. Different affinities of the cis and trans isomer of the ligand were found by surface plasmon resonance (SPR). By in situ irradiation during SPR measurements the effect of the cis-trans isomerization on binding could be monitored in real time.