A photochromic Zn(II) coordination polymer for amine, Fe³⁺, and Al³⁺ sensing and rewritable patterns

Despite notable progress in viologen-based stimuli-responsive materials, achieving greater functional versatility remains a challenge. Herein, a novel photochromic zinc(II) coordination polymer (Zn-complex) was synthesized via solvothermal methods. It has been demonstrated that the colour of the substance changes rapidly and reversibly from yellow to green under UV irradiation. This phenomenon has been attributed to the electron transfer pathway, which has been elucidated by means of surface electrostatic potential (ESP) analysis and DFT calculations. The Zn-complex also functions as a highly discriminative sensor for five amine vapors (NH₃, ethylenediamine, diethylamine, aniline, triethylamine) via distinct colour changes, with the detection mechanism rationalised by comparing the HOMO-LUMO energy levels of the amines. In aqueous solution, it functions as a highly sensitive fluorescent "turn-off" probe for Al³⁺ and Fe³⁺, achieving detection limits of 0.13 μM and 0.30 μM, respectively. Furthermore, the complex enables rewritable inkless printing with patterns that fade within minutes upon water vapor exposure and can be reused over 10 cycles without thermal treatment or extended dark storage.This work thus presents a multifunctional platform for amine discrimination, ion sensing, and rewritable media, highlighting its strong potential for practical stimulus-responsive applications.