Exploring the Intriguing World of Terpyridines: Synthesis, Structural, Optical, and Theoretical Insights Into Bis(p-phenyl-2,2':6',2'')terpyridine

Abstract

Understanding how conformational dynamics influence the physicochemical behaviour of terpyridine-based systems remains a key challenge in materials chemistry. Here, we report the microwave-assisted one-pot and multistep synthesis of a bis(p-phenyl-2,2′:6′,2″-terpyridine) that unexpectedly crystallizes into two stable solid phases identified by powder X-ray diffraction (Bis-TPY-Bulk and Bis-TPY-Crys), corresponding to distinct atropoisomeric conformations. Single-crystal X-ray diffraction establishes an anti–anti arrangement for Bis-TPY-Crys, whereas 1H NMR spectroscopy together with DFT analysis identifies Bis-TPY-Bulk as a symmetric syn–syn conformer. Computational results reveal that the anti–anti form represents the thermodynamic minimum, while the syn–syn conformer constitutes a kinetically trapped state (ΔE = 1.36 eV). The combined experimental and theoretical evidence demonstrates the stabilization of hydrogen-bonded atropisomers through crystallization, providing the first structural description of this behaviour in bis-terpyridine systems. Optical studies further show that conformational locking produces distinct absorption profiles and emission colours in both solution and solid state, establishing a direct relationship between atropoisomerism and photophysical response. These findings highlight conformational control as a powerful strategy for tuning the electronic and emissive properties of terpyridine-based materials.