Improved Photochromic Properties on Viologen-Based Inorganic–Organic Hybrids by Using π-Conjugated Substituents as Electron Donors and Stabilizers

Abstract

A series of inorganic-organic hybrid compounds L(2)(Bi(2)Cl(10)) (L = HMV(2+) = N-proton-N'-methyl-4,4'-bipyridinium for 1, L = HBzV(2+) = N-proton-N'-benzyl-4,4'-bipyridinium for 2, and L = HPeV(2+) = N-proton-N'-phenethyl-4,4'-bipyridinium for 3) have been successfully synthesized by an in situ solvothermal reaction. Compounds 1-3, with the same metal halide as anions but different asymmetric viologen molecules as cations, are ideal model compounds for investigating the detailed effect of different photochromically active molecules on the photochromic properties of the hybrids. Compound 1 shows no photochromic behavior, but compounds 2 and 3 possess photochromism and show a faster photoresponse rate than other reported viologen metal halide hybrids. Studies on the relationship between the structure and photochromic behavior clearly reveal that π-conjugated substituents could be used to improve the photoresponsibility and enrich the developed color efficiently and that the π···π interaction among organic components may not only be a powerful factor to stabilize the viologen monocation radical but also act as the second path of electron transfer from the π-conjugated substituent to the viologen cation for the photochromic process, which significantly influences the photochromic properties.

Experimental (FTIR, Raman, UV–visible and PL) and theoretical (DFT and TDDFT) studies on bis(8–hydroxyquinolinium) tetrachlorocobaltate(II) compound

“…They therefore correspond to electronic transitions in which charge densities move from the 8-HQ organic cations to the CoCl 4 inorganic tetrahedrons. Such transitions are then associated with the Organic toInorganic Charge Transfer phenomenon, labeled here as OICT, which was identified experimentally in some organic-inorganic hybrid materials[59][60][61]. The lowest wavelength at 292.12 nm agrees well with the observed absorption pick of the 8-HQ organic cation.…”

The Impact of Charge‐Distribution on Photochromic Properties in 1D Coordination Polymers

“…After irradiation, the color of 1 shows a new absorption band centered at 700 nm and becomes intense with the increasing of irradiation time (Figure a). According to previous studies of bipyridinium derivatives, these spectral features are attributed to the photoinduced electron‐transfer and formation of the radical species, which is substantiated by ESR studies. As shown in Figure a, 1 exhibits no ESR signals before irradiation but presents single line signals with g = 2.0018 after irradiation.…”

Structurally dependent thermochromism of two iodoargentate hybrids based on the intermolecular charge transfer

“…Consequently, the thermochromic mechanism of 1 and 2 is similar to that of [MCP][Ag 4 I 5 ], which can be ascribed to the temperature effects directly on the population of intermolecular CT [18,19]. It is noteworthy that the more obvious color change of 1 is in good agreement with its larger decreased amplitude of absorption intensity than 2, showing the influence of the bonding features of inorganic chains [55], as well as relative position between organic aromatic nuclei and inorganic moieties on the intermolecular CT [14,19,58,59]. These two 1D iodoargentate chains provide another novel example for the thermochromic iodometallate hybrids.…”

“…Ag1 atom is four-coordinated by two m-I atoms and two m 4 -I atoms in a distorted tetrahedral geometry. The AgeI bond distances range from 2.8237 (5) to 2.9241 (5) Å and IeAgeI bond angles change between 106.077 (14) and 112.758 (14) , which are similar to those of the reported {[pql][Ag 2 I 3 ]} n [41]. The Ag,,,Ag distances (3.2289 (7)e3.3492(7) Å) are much shorter than the van der Waals radius sum of silver (3.44 Å) [42], indicating the existence of argentophilic interactions.…”