Synergistic Photochromism, Fluorescence Switching, and Photomagnetism of Three Mn(II) Complexes Based on a Thiazolothiazole Extended Viologen Derivative

Multifunctional photochromic hybrid materials have attracted great attention due to their wide prospects in information storage, molecular switches, and sensors. Herein, three new photochromic coordination polymers (CPs) with paramagnetic Mn²⁺ ions, namely [Mn₂(TTVP)(<i>m</i>-BDC)₂] (<b>1</b>), [Mn₃(TTVP)(<i>p-</i>BDC)₃(H₂O)₂]·0.5H₂O (<b>2</b>), and [Mn(TTVP)(H₂O)₄]·(4,4'-BPC)·2H₂O (<b>3</b>) have been synthesized (TTVP = 2,5-bis(pyridinium-4-yl)thiazolo[5,4-<i>d</i>]thiazole propionate, <i>m</i>-H₂BDC = isophthalic acid, <i>p-</i>H₂BDC = terephthalic acid, 4,4'-H₂BPC = 4,4'-diphenyldicarboxylic acid). Interestingly, under Ultraviolet (UV) light irradiation, these compounds exhibit distinct photochromic performances due to photoinduced electron transfer (PIET) between aromatic carboxylic acids and TTVP, as validated by spectroscopic and structural analyses. The coloration kinetics and final states are finely tuned by modulating the number and strength of weak interactions between electron donors (EDs) and electron acceptors (EAs). Furthermore, these complexes exhibit photoinduced magnetization enhancement at room temperature, while complexes <b>2</b> and <b>3</b> exhibit reversible fluorescence modulation during the coloration-decoloration cycles. The introduction of photoregulated fluorescent and magnetism into PIET photochromic compounds presents a promising approach for the development of multifunctional materials, holding potential for a range of applications.