The project's aim is to study pathways for photoisomerization of biomimetic organic photoswitches by quantum chemistry methods, using 3-(4-hydroxybenzylidene)-1-methylindolin-2-one as an initial model. For that, potential energy surfaces (PES) of the ground and the first singlet excited states will be investigated with the mixed reference spin-flip method as implemented in the GAMESS program package. The usual pathway for double bond isomerization in the case of oxindole photoswitches is rotation around the C=C bond with possible disturbance of pyramidalization angles of C atoms forming the bond. Thus, The target PES will be built by running a PES scan along principal dihedral (rotational) and pyramidalization angles, and then conical intersections between S0/S1 states are to be found. From a chemical perspective, the removal of a proton from the rotator part often alternates the photoisomerization pathways of such molecules, so similar computations (taking at least a simple solvation model into account, for example, conductor-like polarizable continuum model) are to be done for an anionic form of the photoswitch of interest. The overall computational study should clarify details on the photoisomerization mechanism of the 3-(4-hydroxybenzylidene)-1-methylindolin-2-one, including the potential dependence of such a mechanism on the acidity of the medium.