Shear-Triggered Crystallization and Light Emission of a Thermally Stable Organic Supercooled Liquid

Abstract

Thermodynamics drive crystalline organic molecules to be crystallized at temperatures below their melting point. Even though molecules can form supercooled liquids by rapid cooling, crystalline organic materials readily undergo a phase transformation to an energetically favorable crystalline phase upon subsequent heat treatment. Opposite to this general observation, here, we report molecular design of thermally stable supercooled liquid of diketopyrrolopyrrole (DPP) derivatives and their intriguing shear-triggered crystallization with dramatic optical property changes. Molten DPP8, one of the DPP derivatives, remains as stable supercooled liquid without crystallization through subsequent thermal cycles. More interestingly, under shear conditions, this supercooled liquid DPP8 transforms to its crystal phase accompanied by a 25-fold increase in photoluminescence (PL) quantum efficiency and a color change. By systematic investigation on supercooled liquid formation of crystalline DPP derivatives and their correlation with chemical structures, we reveal that the origin of this thermally stable supercooled liquid is a subtle force balance between aromatic interactions among the core units and van der Waals interactions among the aliphatic side chains acting in opposite directions. Moreover, by applying shear force to a supercooled liquid DPP8 film at different temperatures, we demonstrated direct writing of fluorescent patterns and propagating fluorescence amplification, respectively. Shear-triggered crystallization of DPP8 is further achieved even by living cell attachment and spreading, demonstrating the high sensitivity of the shear-triggered crystallization which is about 6 orders of magnitude more sensitive than typical mechanochromism observed in organic materials.

Stimuli responsive furan and thiophene substituted difluoroboron β-diketonate materials

“…This further demonstrates that the length of an alkyl chain substituent can have substantial effects on thermal properties. 29 …”

A Spin‐Active, Electrochromic, Solvent‐Free Molecular Liquid Based on Double‐Decker Lutetium Phthalocyanine Bearing Long Branched Alkyl Chains

“…In the case of 1 a , only one clear transition, from a glassy state to an isotropic state, was observed below 223 K. On the other hand, 1 b exhibited solid to isotropic liquid transition with a melting point ( T m ) at 332 K (Δ H =27.99 kJ mol −1 , Δ S =0.48 kJ mol −1 K −1 ) in the first heating trace. This transition disappeared in the second heating trace, and instead a glassy transition appeared below 253 K. This behavior is typical for the supercooling phenomenon, where the kinetically trapped supercooled liquid state does not quickly organize into a solid state . The thermodynamically stable solid state of 1 b can be obtained after thirteen additional days of storage at 278 K, which would be the origin of the solid showing melting transition on the first heating process.…”

Correction: Unusual mechanohypsochromic luminescence and unique bidirectional thermofluorochromism of long-alkylated simple DPP dyes

“…The authors would like to add the following citation to their article in order to acknowledge the closely related work reported by Kyeongwoon Chung et al 1 The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.…”