Cold Crystallization and Polymorphism Triggered by the Mobility of the Phenyl Group in Alkyl Azo Dye Molecules

Abstract

The thermal behavior, including the cold crystallization, of alkylderivatized Sudan III (1-[4-(phenylazo)phenylazo]-2-naphthol), SD3-OCn, was investigated. Its structural flexibility due to the two azo groups caused the formation of plural crystal structures, which further resulted in complex cold crystallization. A metastable nonflat structure and a thermodynamically stable flat structure resulted in the two sets of crystallization and melting behavior during the heating process. Further, the change in the alkyl chain length caused variations in the crystallization rate and crystallinity, thus systematically changing the cold crystallization behavior. It was proven that the high mobility of the phenyl group triggered supercooling and cold crystallization and that the alkyl chain correspondingly controlled the thermal behavior.

Effects of alkyl chain length on the cold crystallization of Schiff-base nickel(ii) complexes

“…While the cold crystallization of polymers is well documented, [35][36][37] reports on the cold crystallization of small molecules are scarce. [38][39][40][41] The existing literature suggests that the rotation of aromatic groups hinders crystallization upon cooling, and that molecular flexibility is an important factor for cold crystallization. Nonetheless, the cold crystallization of Schiff-base nickel complexes without aromatic groups, such as OC12-salpn, has been reported.…”

Alkyl substituent-dependent systematic change in cold crystallization of azo molecules

“…In the cold crystallization of small molecules, the mobility of the aromatic rings is considered a factor in supercooling. 18 In previous studies, the diketopyrrolopyrrole (DPP) pigment and azo dye molecules were found to exhibit cold crystallization. 18,19 These molecules have rotatable aromatic rings, and the mobility of the rings leads to polymorphism and/or non-uniform crystallization, resulting in a slow rate of crystallization, supercooling, and cold crystallization.…”

“… 18 In previous studies, the diketopyrrolopyrrole (DPP) pigment and azo dye molecules were found to exhibit cold crystallization. 18,19 These molecules have rotatable aromatic rings, and the mobility of the rings leads to polymorphism and/or non-uniform crystallization, resulting in a slow rate of crystallization, supercooling, and cold crystallization. In the study of the azo molecule, the mobility of the aromatic ring was confirmed as polymorphism and disorder in the single-crystal structures.…”

“…In the study of the azo molecule, the mobility of the aromatic ring was confirmed as polymorphism and disorder in the single-crystal structures. 18 Further investigation is necessary to clarify the mechanism of supercooling and cold crystallization of small molecules. In this study, alkyl groups are introduced at different positions on the aromatic ring to investigate the effect of steric hindrance on the aromatic ring.…”

Cold crystallization and photo-induced thermal behavior of alkyl-derivatized diarylethene molecules

“…[8][9][10][11][12][13][14][15][16] Small molecules oen adopt a low crystallization temperature; therefore, they are suitable for the storage of low-temperature waste heat in society. 17,18 In addition to heat storage, photochemical energy storage has attracted attention. Photochromic molecules are oen used in energy storage.…”