Redox‐Active Metal–Organic Frameworks: Highly Stable Charge‐Separated States through Strut/Guest‐to‐Strut Electron Transfer

Abstract

Molecular organization of donor and acceptor chromophores in self-assembled materials is of paramount interest in the field of photovoltaics or mimicry of natural light-harvesting systems. With this in mind, a redox-active porous interpenetrated metal-organic framework (MOF), {[Cd(bpdc)(bpNDI)]⋅4.5 H2 O⋅DMF}n (1) has been constructed from a mixed chromophoric system. The μ-oxo-bridged secondary building unit, {Cd2 (μ-OCO)2 }, guides the parallel alignment of bpNDI (N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) acceptor linkers, which are tethered with bpdc (bpdcH2 =4,4'-biphenyldicarboxylic acid) linkers of another entangled net in the framework, resulting in photochromic behaviour through inter-net electron transfer. Encapsulation of electron-donating aromatic molecules in the electron-deficient channels of 1 leads to a perfect donor-acceptor co-facial organization, resulting in long-lived charge-separated states of bpNDI. Furthermore, 1 and guest encapsulated species are characterised through electrochemical studies for understanding of their redox properties.

Advanced Photoresponsive Materials Using the Metal–Organic Framework Approach

“…Upon photoexcitation, a pronounced enhancement of conductivity (two orders of magnitude) was observed (Figure b). Apart from these two examples, there are reports on photoinduced CT formation based on host–guest interaction in a powder MOF structure; however, the photoresponsive conductivity was not explored.…”

Nickel(ii) metal–organic frameworks with N,N′-di(4-pyridyl)-naphthalenediimide ligands: influence of secondary building unit geometry on dimensionality and framework dimensions

“…[1][2][3] One approach that has been successfully employed to create such systems are mixed-ligand frameworks where tunable cavities are obtained using a pillaring approach. [12][13][14][15][16]34 Typically pillaring creates three-dimensional frameworks by using rigid linkers (pillars) to connect two-dimensional layers, but the same approach can be used to create twodimensional structures depending on the arrangement of the metal-based secondary building units …”

A two-dimensional CdII coordination polymer based on naphthalenediimide: synthesis, crystal structure and photochromic properties

“…Derivatives of -electron-deficient functional naphthalenediimide (NDI) are efficient electron-transfer mediators due to photoinduced electron transfer from the neutral organic moieties to anion radicals (Langford et al, 2006;Bhosale et al, 2008;Suraru & Wü rthner, 2014). The incorporation of NDI derivatives into coordination polymers has proven an effective method for the construction of photochromic materials (Leong et al, 2014;Sikdar et al, 2015;Xie et al, 2016). For example, three photochromic metal-organic frameworks have been successfully synthesized for inkless and erasable printing using NDIs as organic ligands (Garai et al, 2016).…”