Stentorin is the photoreceptor responsible for both the step-up photophobic response and the negative phototaxis of Stenter coeruleus. Three protein complexes have been isolated from Stenter : stentorin I, stentorin II, and stentorin IIB. The structure of the chromophore for each of these complexes was investigated using surface-enhanced Raman scattering (SERRS) spectroscopy. The chromophore of each complex was found to be identical or very similar to that of the free stentorin chromophore isolated from stentorin I. In addition, it was found that SERRS can easily distinguish stentorin from the photodynamic pigment hypericin, even though the two structures are very similar.