Photochemistry is an important multidisciplinary scientific discipline due to numerous applications of photochemistry in modern technologies. The proposed project is focused on the study of several fundamental photochemical reactions, as well as in finding applications of these reactions in organic synthesis and biology. The work will involve three research topics, excited state proton transfer from nitrogen atom as an acidic site, photoheterolysis of different aniline derivatives for the development of new photocleavable protective groups in organic chemistry (photocages), and development of novel photo-treatments of cancer, investigated on several classes of molecules: carbazoles, oligopeptides and BODIPY derivatives. The investigation comprises four working packages: A) synthesis of new precursor molecules, B) investigation of photochemical reactivity of these molecules and finding applications of photochemical reactions in organic synthesis, C) investigation of photochemical reaction mechanisms by spectroscopic techniques and computations, and D) investigation of biological activity. The proposed project is primarily fundamental research in the field of organic chemistry. Therefore, the research activities will lead to discoveries that will have an impact by increasing general knowledge in organic chemistry, photochemistry, supramolecular and medicinal chemistry. In addition to the fundamental character of the proposed investigation, we will look for the applications and go beyond the state of the art in the discovery of new photo-activable drugs. The PhotoApp team is expected to find a number of lead molecules with antiproliferative activity, providing possibilities for further research and potential development of new methodologies for treating cancer with minimal side effects, potentially impacting the whole society in general.