A C3-Symmetric Structurally Twisted Molecular Architecture: Mechano-/Fluorochromic Behavior and Selective Multiphase Detection of Pd(II)

Abstract

Triaminoguanidinium (TG)-based C₃-symmetric-like molecular architectures with diverse donors and acceptors are well established as organic molecular materials for promising stimuli-responsive and metal sensing-based applications. However, the mechanofluorochromic (MFC) response was unremarkable upon applying external mechanical stress. Even though some show MFC features, there was no optical shift under ambient light. In this paper, we developed a novel C₃-symmetric molecule, TAC₃, containing the TG core linked with conformationally twisted thiophene-linked anthracenyl terminals. Three conformationally deformed hands in TAC₃ respond against external mechanical stimuli with a redshifted absorption and emission, easily detectable through the naked eye. Although MFC features were reported before for such C₃-symmetric molecules, the change in absorbance was not identified. In addition, TAC₃ could selectively detect Pd²⁺ through extreme emission quenching (green to black). The mechanochromism and sensing outcomes are elucidated by the experimental and theoretical support. Compared to the previous reports, the notable 2 : 3 (metal: ligand) binding due to geometric restriction creating a specific pocket size for Pd⁺² is unusual for this system. The onsite application on Pd²⁺ detection and measurable MFC features are demonstrated to validate the potential of this C₃-symmetric molecule in advanced optoelectronic applications such as security writing and Pd²⁺ ion detection.