This dissertation covers new concepts for the biological application of functionalized photochromic dithienylethenes, which act as light-dependent switches for enzyme activity and peptides. The development of dithienylcyclopentene-based enzyme inhibitors is reported, which can reversibly control the activity of the key metabolic enzyme mtPriA by light. Furthermore, the application of photochromic dithienylcyclopentenes as cell signaling inhibitors for the cascade of extracellularly regulated kinase has been described. In order to improve water solubility, increase hydrophilicity and achieve easier derivatization, dithienyl maleimide based amino acids were synthesized and incorporated into peptides. In addition, new photochromic dithienyl-maleic hydrazides will be introduced. The knowledge gained is of particular relevance with regard to the development of novel molecular tools to control cellular processes through light.