 Franck assisted Frederick Lindemann in helping dismissed Jewish scientists find work overseas , before he left Germany in November 1933 . After a brief visit to the United States , where he measured the absorption of light in heavy water with Wood at Johns Hopkins University , he took up a position at the Niels Bohr Institute in Copenhagen . He needed a new collaborator , so he took on Hilde Levi , whose recent thesis had impressed him . His original intention was to continue his research into the fluorescence of vapours and liquids , but under Bohr 's influence they began to take an interest in biological aspects of these reactions , particularly photosynthesis , the process by which plants use light to convert carbon dioxide and water into more organic compounds . Biological processes turned out to be far more complicated than simple reactions in atoms and molecules . He co @-@ authored two papers with Levi on the subject , which he would return to over the following years . 
