Reversible martensitic transitions in molecular crystals are an unusual phenomenon, and most of the cases reported in the literature occur at relatively low temperatures. The title compound, 2-(5-(benzo[d]thiazol-2-yl)-1,3,4-oxadiazol-2-yl)-5-(diethylamino)phenol (DBOX), reveals an interesting and rich polymorphism, characterized by a reversible single-crystal-to-single-crystal transition occurring at 185 degrees C. The transition can be repeated several times on a single crystal without degradation and/or damage. The crystal structure of this high-temperature phase (II) and two low-temperature polymorphs (I and III) are solved by single-crystal X-ray analysis to fully elucidate the mechanism of the reversible I -> II transition. Changes in the molecular packing are preceded by anomalous thermal expansion and evolve as slipping/rotation motions of molecular dimers, activated by steric disengagement along the anomalous expansion direction and resulting in the reversible contraction of the long crystal axis and lateral expansion. Uncommon panchromatic- and white-emitting fluorescence properties of the reported compound are also described.
High-Temperature Reversible Martensitic Transition in an Excited-State Intramolecular Proton Transfer Fluorophore
Lettieri Stefano;
2019
Abstract
Reversible martensitic transitions in molecular crystals are an unusual phenomenon, and most of the cases reported in the literature occur at relatively low temperatures. The title compound, 2-(5-(benzo[d]thiazol-2-yl)-1,3,4-oxadiazol-2-yl)-5-(diethylamino)phenol (DBOX), reveals an interesting and rich polymorphism, characterized by a reversible single-crystal-to-single-crystal transition occurring at 185 degrees C. The transition can be repeated several times on a single crystal without degradation and/or damage. The crystal structure of this high-temperature phase (II) and two low-temperature polymorphs (I and III) are solved by single-crystal X-ray analysis to fully elucidate the mechanism of the reversible I -> II transition. Changes in the molecular packing are preceded by anomalous thermal expansion and evolve as slipping/rotation motions of molecular dimers, activated by steric disengagement along the anomalous expansion direction and resulting in the reversible contraction of the long crystal axis and lateral expansion. Uncommon panchromatic- and white-emitting fluorescence properties of the reported compound are also described.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.