Effect of counter cations on the photochromic behaviors of three Zn–viologen complexes

Abstract

To determine the influence of counter cations on the photochromic properties of viologen-based compounds, with the self-assembly reaction of different viologen cations (MV²⁺ = 1,1′-bis(methyl)-4,4′-bipyridinium dication, EV²⁺ = 1,1′-bis(ethyl)-4,4′-bipyridinium dication, PV²⁺ = 1,1′-bis(propyl)-4,4′-bipyridinium dication), Zn²⁺ and H₃BTC (1,3,5-benzenetricarboxylic acid), three complexes (MV)_0.5[Zn(BTC)(H₂O)₅]·2H₂O (1), (EV)_0.5[Zn(BTC)(H₂O)₅]·H₂O (2), and (PV)_0.5[Zn(BTC)(H₂O)₅]·H₂O (3) have been synthesized and structurally characterized. The photochromic behavior of the three compounds has been investigated due to the presence of electron-deficient viologen fractions. Compounds 1–3 feature similar isolated structures and all exhibit electron-transfer (ET) photochromism, which can be fine-tuned by introducing different counter cations.