Crystals of 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole and Its Derivative with Terminal n-Hexyl Substitutes: Growth, Structure, Thermal and Absorption-Fluorescent Properties

Abstract

This study presents an investigation into the crystallization and absorptive-fluorescent properties of linear conjugated molecules derived from 2,1,3-benzothiadiazole, specifically 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Ph-Xy-BTD) and 4,7-bis(4'-hexyl-2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Hex-Ph-Xy-BTD). The synthesis of a new derivative of Hex-Ph-Xy-BTD is described. It was found that the presence of terminal n-hexyl substituents in Hex-Ph-Xy-BTD leads to a lower melting point, increased solubility and has a positive effect on crystallization compared to Ph-Xy-BTD. Single crystals of Hex-Ph-Xy-BTD were grown from hexane solution, and their structure was elucidated using single-crystal X-ray diffraction, confirming a monoclinic system (space group P21/c, Z = 4). Absorption and fluorescence spectra were obtained and analyzed for solutions in tetrahydrofuran as well as for the crystals of Ph-Xy-BTD and Hex-Ph-Xy-BTD, alongside investigations of quantum yield and fluorescence lifetime.