In Paris, he joined the "Équipe" group. In this way he met influential artists, such as Robert Delaunay and Albert Gleizes. There, he helped the Resistance against the German occupiers. By the end of the war, he lived in various places in southern France, especially in Graulhet, Tarn (department). Several times he was interned, then in camp, "Les Milles" in Aix-en-Provence, from which he managed to escape, in October 1940. At the end of 1944, Adolf Fleischmann returned from his hideout in southern France back in liberated Paris, where he found a completely devastated studio, with only remnants of his paintings, the work of many years. He literally, "I experienced a nervous breakdown." But with the help of his French friends, he could soon begin his artistic work again, and get involved until his emigration to the U.S. in 1952, participated in exhibitions in Paris. Under the pressure of a violent anti-German feeling, he signed in the early postwar period works with the pseudonym Richard, his middle name. In the catalog of Realitéts Nouvelles No. 1, 1947, is a picture of him. He did not use the pseudonym of Richard in the United States. At the end of the war and in the early postwar years had a brief first Fleischmann "geometric phase" in the sense of concrete art, which he resigned but was soon in favor of less stringent designs. He joined the group at Réalités nouvelles and moved to Paris for a few years. He earned his living with designs for posters, magazine titles, wallpaper and fabrics (such as towels for Dior). In 1948, he married Elly Abendstern, and in the same year he had his first solo exhibition in the gallery Creuze in Paris. In 1950, Fleischmann wrote again to the geometric shape, but less in terms of concrete art, but rather in the context of serial painting. He thus became an early precursor of Op Art. At the age of nearly 60 years he had developed his own distinctive style, characterized by rhythmic grouped narrow strips that are integrated into narrow angle. In 1951 he exhibited his latest works at the Galerie Colette Allendy. He was a member of American Abstract Artists. Then he was offered better job opportunities in the U.S., he moved to New York in 1952. Here he lived both as a staff artist, at the College of Physicians and Surgeons of Columbia University, as well as a freelance painter.