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A new class of deep eutectic solvents are presented which exhibit all of the physical characteristics of classical deep eutectic solvents, with the exception that one of the components is volatile when exposed to the atmosphere at room temperature. This enables a premeditated, auto-destructive capability which can lead to novel crystalline identities. We demonstrate the effectiveness of this concept through the room-temperature crystallisation of a broad range of organic molecules, with a particular focus on pharmaceuticals, that possess a variety of functional groups and molecular complexity. Furthermore, we show how, through the simple altering of the eutectic composition, polymorphism in paracetamol can be controlled, enabling the elusive metastable form II to spontaneously crystallise at room temperature.Born from the class of solvents known as ionic liquids, the deep eutectic solvents (DESs), named from the Greek "εu" (eu = easy) and "τήξις" (teksis = melting), have been an increasingly well-researched class of solvents for the last two decades. They have been a boon to catalysis, extraction processes, electrochemistry, organic synthesis and in the creation of more efficient batteries and dye-sensitized solar cells. [1][2][3][4][5][6][7] Originally conceived as a greener and cheaper alternative to the more toxic and less environmentally friendly ionic liquids, 8,9 DESs Supporting Information Table S1 and Figures S1 -S21 Accession Codes CCDC 1879336 and CCDC 1879689 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Herein we demonstrate the prowess of the 3D electron diffraction approach by unveiling the structure of terrylene, the third member in the series of peri‐condensed naphthalene analogues, which has eluded structure determination for 65 years. The structure was determined by direct methods using electron diffraction data and corroborated by dispersion‐inclusive density functional theory optimizations. Terrylene crystalizes in the monoclinic space group P21/a, arranging in a sandwich‐herringbone packing motif, similar to analogous compounds. Having solved the crystal structure, we use many‐body perturbation theory to evaluate the excited‐state properties of terrylene in the solid‐state. We find that terrylene is a promising candidate for intermolecular singlet fission, comparable to tetracene and rubrene.