Falk's main research area is the structural analysis, synthesis, stereochemistry and photochemistry of plant and animal photosensitizing and photosensory pigments. The main group of compounds covered in his work are pigments derived from the fundamental phenanthro[1,10,9,8-opqra]perylene-7,14-dione chromophore with natural pigments like hypericin, stentorin, the fringelites, the gymnochromes, and blepharismin. In addition, he is focusing on hemin-analogous corrphycene derivatives (e.g. as potential blood substitutes and heme oxygenase blocker) as well as on other natural compounds such as the natural sun blocker urocanic acid. Furthermore, research on applied problems of industrial relevance, like oxidation, ozonization, non natural amino acids and catalysis have been pursued.