Solid-State Supramolecular Inclusion Complexes of β-Cyclodextrin with Carboxyphenyl Viologens Showing Photochromic Properties

Abstract

β-Cyclodextrins (β-CDs) are shown to form 1:1 and 2:1 host−guest inclusion complexes with two carboxyphenyl viologens, 1-(4-carboxyphenyl)-4,4′-bipyridinium chloride (1 + • Cl − ) and 1,1′-bis(4-carboxyphenyl)-4,4′-bipyridinium dichloride (2 2+ •Cl 2 − ), in an aqueous solution. The solid-state supramolecular host−guest inclusion complexes 1 + @β-CD and 2 2+ @β-CD 2 demonstrate excellent photochromic properties. The results of the electron-spin resonance (ESR) spectroscopy suggest that their photochromic behaviors are caused by the generation of free radicals (V •+ ). The energy-minimized structure and the calculated reorientation energy of the inclusion complex 1 + @β-CD support the electron transfer from the host β-CD to the guest 1 + . The practical applications of the inclusion complex 1 + @β-CD as erasable inkless printing media and an anticounterfeiting material were also studied. The present study provides a supramolecular method for the construction of photochromic materials.

Applications of Viologens in Organic and Inorganic Discoloration Materials

“…In addition, this mixed matrix film also has good ductility, which makes us believe that the application prospect of M −1 device in the field of UV detection is very broad (Figure 11e). In 2022, Liu′s group also reported two viologen‐based compounds with excellent photochromic ability [107] . Under the irradiation of 300 W Xe lamp, both 1 + @β‐CD and 2 2+ @β‐CD 2 were found to have similar photochromic behaviors, and the color change of 1 + @β‐CD was from gray white to dark blue, and surprisingly it was found that the color change was basically saturated within 3 min (Figure 11f).…”

“…(g) Erasable inkless printing on the 1 + @β‐CD‐coated filter paper [107] . (h) QR code recognized by a smartphone [107] . (i–j) UV‐Vis spectra of compound 1 under a Xe lamp or blue ray.…”

“…Reprinted with permission from Ref. [106] (Copyright 2016, Royal Society of Chemistry), [98] (Copyright 2021, Wiley Online Library, [107] (Copyright 2021, American Chemical Society), [108] (Copyright 2021, Royal Society of Chemistry).…”

“…(e) Flexibility of M‐1 [98] . (f) Color changes of 1 + @β‐CD and 2 2+ @β‐CD 2 under Xe lamp irradiation [107] . (g) Erasable inkless printing on the 1 + @β‐CD‐coated filter paper [107] .…”

“…(f) Color changes of 1 + @β‐CD and 2 2+ @β‐CD 2 under Xe lamp irradiation [107] . (g) Erasable inkless printing on the 1 + @β‐CD‐coated filter paper [107] . (h) QR code recognized by a smartphone [107] .…”