Influence of Positional Isomerism on Modulating Crystal Packing and Physicochemical Properties of New Picolylamine-Based Fully Organic Ionic Salts

Abstract

The selective formation of positional isomers, along with the fine-tuning of physicochemical properties through structural variation, represents an effective crystal engineering strategy for the development of thermally stable and photoactive organic materials. Here in this report, three new fully organic ionic salts (namely, 2-picolylaminium p-toluenesulfonate; [2P][OTs], 3-picolylaminium p-toluenesulfonate; [3P][OTs], and 4-picolylaminium p-toluenesulfonate; [4P][OTs] based on the positional isomers of picolyl-amine as cation, and tosylate as anion have been synthesized in a single-step with atom economy at room temperature and are characterized by multinuclear NMR and HRMS techniques. Single-crystal X-ray diffraction (SCXRD) studies revealed a zig–zag fashion arrangement of cations in [2P][OTs], whereas [4P][OTs] exhibited a linear arrangement of cations within their crystal lattices. Raman spectroscopy further highlighted isomer-dependent shifts in the vibrational modes of the tosylate anions, suggesting that the positional variation of the functional group in the cation significantly influences the local ionic environment. Furthermore, the results of photophysical investigations show [3P][OTs] and [4P][OTs] are emissive in the solid state. However, [2P][OTs] do not show any visible fluorescence. The outcomes of this study emphasize the importance of positional isomerism for the rational design of desired materials. © 2025 The Author(s). ChemistrySelect published by Wiley-VCH GmbH.