Elucidating the Effects of Fluoro and Nitro Substituents on Halogen Bond Driven Assemblies of Pyridyl-Capped π-Conjugated Molecules

Among recent advances toward efficient semiconducting materials, rational design guidelines have emerged focusing on the synergy between various intermolecular interactions to improve the solid-state order of pi-conjugated molecules in organic electronic devices. Herein, we focus our attention on halogen bonding (XB) interactions and the crucial role of electron withdrawing substituents (e.g., nitro and fluoro) toward influencing solid-state properties via secondary interactions. Employing iodoethynyl benzene derivatives (F(2)BAI and (NO2)(2)BAI) and thiophene/furan-based building blocks equipped with pyridyl groups as self assembling domains (PyrTF and PyrT(2)), co-crystals driven by XB and pi-stacking interactions were formed and studied. Spectroscopic and thermal analysis of 1:1 mixtures provide initial evidence of co-crystallization. X-ray crystallography affords the inherent solid-state packing motifs within each assembly. Computational studies support experimental observations, revealing the dominant interactions and contribution of each substituent group toward increasing the stability of the resulting assemblies.