Highly condensed, fully conjugated aromatic compounds are interesting candidates for application in organic electronics. Their electronic properties improve with increasing crystallinity. Here it is shown that the crystallization of three archetypes of such molecules - pentacentetron, indigo and perinone - can be achieved hydrothermally. This finding is extremely astonishing in view of the structure of these compounds. Furthermore, it is shown that perinone can be produced from naphthalene bisanhydride and o ‐ phenylenediamine in exclusively high-temperature water and without the addition of cosolvents or catalysts. Furthermore, the transformation can be accelerated drastically through the use of microwave radiation.