Systematical Investigation of Chain Length Effect on the Melting Point of a Series of Bifunctional Anthraquinone Derivatives via X-ray Diffraction and Scanning Tunneling Microscopy

Abstract

Introducing a continuously changing alkyl chain is effective to modify the conjugated molecule, which is widely used in studying the diversity of two-dimensional (2D) self-assembly and the performance of three-dimensional (3D) bulk materials. In this study, a series of bifunctional anthraquinone derivatives (A-OC n , n = 3−18) are synthesized to investigate the interrelation between the chain length and the melting point by differential scanning calorimetry (DSC). It is observed that the A-OC n (n = 1 and 4) crystallizes in monoclinic and the A-OC n (n = 3, 5, 6) crystallizes in triclinic by single-crystal X-ray diffraction (XRD). With the help of scanning tunneling microscopy (STM), the A-OC n (n = 7−18) is found to exhibit an odd−even alternation in their self-assembled structures. The theoretical calculations for crystal structures and the packing density analyses for selfassembly indicate that the hydrogen bond strength gradually reduces with the increase of the chain length, while the van der Waals interaction is opposite. Namely, the hydrogen bonds and the van der Waals interactions coregulate the variation of melting points. In general, this work provides an understanding at the molecular level on how alkyl chain length regulates the melting point, and we believe that it will have implications for the optimization of future organic materials.

Alkyl-Engineered Dual-State Luminogens with Pronounced Odd–Even Effects: Quantum Yields with up to 48% Difference and Crystallochromy with up to 22 nm Difference

“…This odd–even effect in melting point is ascribed to the different packing modes of alkanes in the solid state . A similar alternative melting point is also observed in alkyl chain-engineered functional materials . Besides the melting point, the odd–even effects in other material properties such as solubility, nanoparticle morphology, endothermic enthalpy, phosphorescence lifetime, and crystal structures are also reported.…”

9,10-Anthraquinones Disubstituted with Linear Alkoxy Groups: Spectroscopy, Electrochemistry, and Peculiarities of Their 2D and 3D Supramolecular Organizations

“…However, the X-ray and the STM data are separated in such a manner that the former are presented for shorter substituents (from butoxy to hexyloxy), whereas the latter are limited to longer substituents (from heptyloxy to octadecyloxy). The present paper is complementary to ref , since in addition to detailed electrochemical results it provides complete STM and X-ray data for Anth derivatives with substituents varying in the range from butoxy to dodecyloxy. This set of results not only allows for establishing the relationship between the 3D organization in single crystals and the 2D one in monolayers but also demonstrates that along with the increasing length of the substituent the effect of the graphite substrate symmetry on the resulting 2D supramolecular organization becomes more pronounced.…”

“…Several papers on Anth-containing alkoxy groups have been published to date, including those reporting STM investigations on monosubstituted, 34 disubstituted, 35 and trisubstituted 36 derivatives. In particular, a very recently published, extremely interesting paper 37 describes 3D and 2D structural properties of dialkoxy-substituted Anth. However, the X-ray and the STM data are separated in such a manner that the former are presented for shorter substituents (from butoxy to hexyloxy), whereas the latter are limited to longer substituents (from heptyloxy to octadecyloxy).…”

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

“…Accordingly, the alkylation of rigid molecules can alter their physical properties [1][2][3][4][5][6][7][8][9][10][11] significantly, including their thermal properties, [12][13][14][15] crystal structure, [16][17][18][19][20][21] and the structure of adsorbed monolayers. [22][23][24][25][26][27][28] We have analyzed the thermal properties of salen derivatives bearing alkyl chains of variable length and found that those with alkoxy groups adopt a liquid crystalline state at varying temperatures depending on the alkyl chain length. 29,30 In contrast, OC12-salpn, a salen derivative with a methyl group introduced as steric bulk, exhibited cold crystallization.…”