The modulation effect of pi–pi interactions on the electronic and photochromic properties of viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium

Abstract

Two viologen complexes containing BCEbpy were prepared and displayed excellent photo-response properties by the modulation effect of pi–pi interactions.

Photo/Electrochromic Dual Responsive Behavior of a Cage-like Zr(IV)-Viologen Metal–Organic Polyhedron (MOP)

“…The result shows that no ESR signal could be observed before irradiation, while a strong g = 2.0016 signal appears in Zr-MOP-1 after irradiation (Figure 3). The g value is consistent with that of a free electron (2.0023) observed in previous viologen/bipyridinium complexes, [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]73 indicating that the photochromism is more likely to originate from the generation of photoinduced free radicals. In other words, the bipyridinium ligand L is indeed reduced to produce L* free radicals after irradiation.…”

“…The original sample of Zr-MOP-1 displays intense absorption bands below 400 nm, confirming the n−π* and π–π* transitions of the aromatic organic ligands, and the absorbance smoothly decreases in the visible light region. After irradiation, three new bands centered at 452, 658, and 750 nm appeared, which indicates the generation of viologen radicals via ET under UV light, − and these absorption peaks became intense during the irradiation and tended to become saturated after illumination for 30 min (Figure a). The extrapolated photochemical gap energy ( E g = 1.72 eV) of Zr-MOP-1 was obtained on the basis of its diffuse reflectance spectrum (Figure S3), which is consistent with the absorption band at 750 nm, corresponding to the energy of electron transfer (1.64–3.19 eV) of this kind of compound.…”

“…The electron donors near the pyridinium units might all have the potential to transfer electrons to the pyridinium rings and facilitate the generation of free radicals. In addition, the distances and directions of the D···A and π···π interactions and the C–H···π interactions, the suitable D···A angles, and the tightly condensed packing mode all have an influence on the ET process and the formation of free radicals in such solid materials. − For the viologen-based crystalline materials, the nitrogen atoms in pyridinium rings are electron-deficient, while oxygen atoms of the carboxylate group (as well as solvent molecules such as H 2 O, DMF, and CH 3 OH) are electron-rich, which is usually identified as an excellent electron donor under photoirradiation. Usually, the contact between the carboxylate O donor and the pyridinium N acceptor is considered one of the ideal pathways for electron transfer to produce free radicals.…”

“…External stimuli could trigger the generation of free radicals by transferring an electron from the donor to the viologen moiety, resulting in the reversible redox behavior along with the change in color. In this respect, fruitful crystalline materials with fascinating structures and chromic manners based on viologen derivatives have been achieved in recent decades. − …”

A Series of Polyoxometalate‐Viologen Photochromic Materials for UV Probing, Amine Detecting and Inkless and Erasable Printing

“…At present, a series of viologen based metalorganic complexes have been obtained, which can exhibit good photochromic properties and amine detection performance. [14][15][16][17][18] However, the combination of viologen and POMs to build new photochromic materials and amine detection materials were rarely observed. Up to now, only a few reports on this series were reported.…”