title: High Sensitivity Viologen for a Facile and Versatile Sensor of Base and Solvent Polarity in Solution and Solid State in Air Atmosphere.
abstract: Viologen cations are excellent electro- and photochromic materials. They generally have no response or very low sensitivity to bases. In this paper, three compounds, 1,1'-bis(2-oxo-2-phenylethyl)-4,4'-bipyridinium (viologen) with different substituents, including H (1), Cl (2), and OH (3), were synthesized. All three, especially 1 and 2, have very high sensitivity to base in both solution and solid state in air atmosphere. These viologens are responsive not only to bases but also to solvent polarity. NMR shows 1 became enolic and then a radical, whereas 3 is colored only in the radical form. These results are in agreement with EPR spectra. Crystal structures show that the C-C that links two pyridinium and N-C distances in coplanar pyridinium in the colored (radical) form is clearly longer than that of the pale-yellow form, indicating that the color is due to the viologen radical. Viologens containing an electron-withdrawing phenacetyl group are the most sensitive compounds for fast, naked eye detection of base and solvent polarity.
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Shi
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Feifei
authors.initials: F
authors.lastname: Xing
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Yue-Ling
authors.initials: YL
authors.lastname: Bai
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Meiling
authors.initials: M
authors.lastname: Hu
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Ming-Xing
authors.initials: MX
authors.lastname: Li
authors.affiliation: Innovative Drug Center, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China.
authors.forename: Shourong
authors.initials: S
authors.lastname: Zhu
keywords: air-stable; electronic effect; solvatochromic; viologen; visual base sensor