Two novel multifunctional chromic compounds: Synthesis, photochromism, ammonia sensing, and anion sensing

Two new Zn (II)-viologen chromic compounds, named {[(4-BCBPY)0.5(HIPA)]·H2O}n (1) and {[Zn3(IPA)4(4-BCBPY)]·2H2O}n (2) (4-BCBPY2+ = 1,1'-bis(4-cyanobenzyl)-4,4'-bipyridinium dication, H2IPA = isophthalic acid) have been synthesized through varying reaction conditions. Structural analysis reveals that compound 1 possesses a supramolecular compound, while compound 2 exhibits a metal-organic framework (MOF) structure built from trinuclear metal building units. Under the irradiation of a 300 W Xe lamp, compound 1 undergoes a color change from orange to brown, while compound 2 transitions from yellow to green. The introduction of metal ions in compound 2 enhances its light response rate compared to compound 1. Additionally, compound 2 displays a visible color change in the presence of ammonia, whereas compound 1 does not exhibit this capability. Meanwhile, the stable product 2P of 2 was obtained through irradiation, and the structural differences between 2 and 2P were analyzed. Furthermore, the study of time-dependent density functional theory (TDDFT) provides theoretical support for understanding the properties of 1 and 2. Both compounds exhibit intriguing photomodulated luminescence properties and demonstrate remarkable sensing abilities toward Cr2O72−. Notably, the introduction of metal ions was found to modulate the photochromic behavior as well as the ammonia/anion sensing properties of these compounds.