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The true molecular conformation and the crystal structure of benzo[ e ]dinaphtho[2,3- a ;1′,2′,3′,4′- ghi ]fluoranthene, 7,14-diphenylnaphtho[1,2,3,4- cde ]bisanthene and 7,16-diphenylnaphtho[1,2,3,4- cde ]helianthrene were determined ab initio by 3D electron diffraction. All three molecules are remarkable polycyclic aromatic hydrocarbons. The molecular conformation of two of these compounds could not be determined via classical spectroscopic methods due to the large size of the molecule and the occurrence of multiple and reciprocally connected aromatic rings. The molecular structure of the third molecule was previously considered provisional. These compounds were isolated as by-products in the synthesis of similar products and were at the same time nanocrystalline and available only in very limited amounts. 3D electron diffraction data, taken from submicrometric single crystals, allowed for direct ab initio structure solution and the unbiased determination of the internal molecular conformation. Detailed synthetic routes and spectroscopic analyses are also discussed. Based on many-body perturbation theory simulations, benzo[ e ]dinaphtho[2,3- a ;1′,2′,3′,4′- ghi ]fluoranthene may be a promising candidate for triplet–triplet annihilation and 7,14-diphenylnaphtho[1,2,3,4- cde ]bisanthene may be a promising candidate for intermolecular singlet fission in the solid state.