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Two-Dimensional Silver-Thiocyanate Layers Directed by Viologens: Structural Transformations upon Low Pressure Stimuli, Piezochromic Luminescence, Photocurrent Responses, and Photocatalytic Properties

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journal contribution
posted on 29.11.2018, 00:00 by Kai-Yue Song, Li-Ming Zhao, Wen-Ting Zhang, Yi Li, Hao-Hong Li, Zhi-Rong Chen
The reactions of AgSCN with excess KSCN in the presence of linear viologens templates afford seven new hybrids, {(MV)­[Ag4(SCN)6]}n (1), {(MV)­[Ag2(SCN)4]}n (2), {(EV)­[Ag4(SCN)6]}n (3), {(EV)­[Ag2(SCN)4]}n (4), {(BV)­[Ag4(SCN)6]}n (5), {(CMV)­[Ag2(SCN)4]}n (6), and {(BMPE)­[Ag2(SCN)4]}n (7) (MV2+ = methyl viologen, EV2+ = ethyl viologen, BV2+ = benzyl viologen, CMV2+ = cyanomethyl viologen, BMPE2+ = 1,2-bis­(N-methylpyridiniim-4-yl)­ethane). The silver-thiocyanate skeletons with the formula of [Ag4­(SCN)6]n2n and [Ag2(SCN)4]n2n are the scarce representative examples of the two-dimensional (2-D) polypseudorotaxane arrays penetrated (for 16) or intercalated (for 7) by viologen dications. Upon an external low pressure stimulus, the 2-D silver-thiocyanate layers penetrated by cations exhibit looser packing with longer Ag–S­(N) bond lengths, weaker charge transfer (CT) interactions, and larger cavities, but the contrary trend can be found on the compound with intercalated organic cations. Due to the strong CT interactions between viologens and silver-thiocyanate skeletons, the CTs can occur at room temperature. Interestingly, 7 represents typical reversible piezochromic luminescence behavior. In addition, they show excellent photocurrent responses and efficient photocatalytic degeneration performances on organic dyes. Finally, their band structures and density of states before and after compression based on density functional theory calculations were executed to correlate their properties.