By this time, he was a famous botanist, an author of publications concerning the taxonomy and uses of lichens and willows (Salix), as well as two editions of «Deutschlands Flora» (the manuscript of the third edition was lost in the fire of 1812). In Moscow, Hoffmann published a classical monograph «Genera Plantarum Umbelliferarum» (1814, 1816), a description of the Botanical Garden of Moscow University (1808; 3528 species), and several other important papers. Hoffmann was also a famous lecturer - both Goethe and Humboldt attended his lectures at Goettingen University, as well as a talented plant illustrator, preparing many excellent plant images for his various books himself.

Hoffmann had accumulated at Goettingen, and taken with him to Moscow, an extensive herbarium collection and library. The herbarium included a small number of specimens that he had collected himself before moving to Moscow and many important collections made by other botanists: V.A. von Haller, J.A. Murray, A.J. Hugo, J.F. Ehrhart, J.R. Forster and J.G. Forster, J.J. Dickson, D.H. Hoppe, C.P. Thunberg, and J.E. Smith. These collections were not incorporated into Hoffmann's personal herbarium.

Hoffmann's herbarium and his other collections fortunately survived the Moscow Fire in 1812 because they were kept neither in Moscow University nor in Hoffmann's house, but in the Moscow Military Medical-Surgical Academy. Hoffmann's library and manuscripts were destroyed by fire in his house. The herbarium was housed at the Academy after 1812 too, perhaps because Hoffmann held lectures there and, from 1817, he was a Professor of the Academy in addition to his position at the University. Now the majority of Hoffmann's collections are kept at the Herbarium of Moscow University (MW).

Hoffmann himself collected very few plants in Russia. However, he continued to acquire collections made by other botanists, rearranging his specimens and organising their labelling during his stay in Moscow. The structure of Hoffmann's collection was therefore created in Russia. Unfortunately, he usually replaced original labels of other botanists by abbreviated copies which he made himself. However, in 1825, he published a catalogue of his personal collection which is very important because in many cases it contains more information than was recorded on the labels of the herbarium specimens. A copy of the catalogue is kept in the MW Herbarium.

Hoffmann was commemorated in genera Hoffmannia Sw. 1788 (Rubiaceae) and Hoffmannia Willd. 1789 (= Psilotum, Psilotaceae).