The photoisomerization or other photochemical reactions of specialized molecules, such as azobenzenes, norbornadienes, or dihydroazulenes, depend critically on electronic structure changes that occur upon photon absorption. We will show how quantum mechanical-molecular mechanical methods can used to model these systems. The electronically active region (the molecule undergoing photoisomerization) is handled with high-level quantum mechanical (QM) methods, while simultaneously representing the surrounding environment (e.g., solvent, substrate, or other molecular components) using computationally efficient molecular mechanics (MM).