Synthesis of dipolar molecular rotors as linkers for metal-organic frameworks

Abstract

We report the synthesis of five dicarboxylic acid-substituted dipolar molecular rotors for the use as linker molecules in metal-organic frameworks (MOFs). The rotor molecules exhibit very low rotational barriers and decent to very high permanent, charge free dipole moments, as shown by density functional theory calculations on the isolated molecules. Four rotors are fluorescent in the visible region. The linker designs are based on push–pull-substituted phenylene cores with ethynyl spacers as rotational axes, functionalized with carboxylic acid groups for implementation in MOFs. The substituents at the phenylene core are chosen to be small to leave rotational freedom in solids with confined free volumes. The dipole moments are generated by electron-donating substituents (benzo-1,3-dioxole, benzo-1,4-dioxane, or benzo-2,1,3-thiadiazole annelation) and withdrawing substituents (difluoro, or dicyano substitution) at the opposite positions of the central phenylene core. A combination of 1,4-dioxane annelation and dicyano substitution generates a theoretically predicted, very high dipole moment of 10.1 Debye. Moreover, the molecules are sufficiently small to fit into cavities of 10 Å3. Hence, the dipolar rotors should be ideally suited as linkers in MOFs with potential applications as ferroelectric materials and for optical signal processing.

GIWAXS Characterization of Metal–Organic Framework Thin Films and Heterostructures: Quantifying Structure and Orientation

“…For example, we are working on the creation of a UiO‐type MOF film with highly dipolar linkers, initially reported by Hamer et al. [ 29 ] A vapor‐phase assisted synthetic protocol using the dicyanobenzodioxane dipolar rotor linker led to ordered peaks being observed in out‐of‐plane XRD scans. However, the GIWAXS data of the fabricated structure (in Figure S3, Supporting Information) do not qualitatively agree with that expected from a UiO topology; the wide array of off‐axis peaks is missing.…”

“…As a brief remark closing this section, the considerable number and distinct pattern of peaks visible in GIWAXS for UiO-type structures make it possible to qualitatively check whether the expected topology is growing or not. For example, we are working on the creation of a UiO-type MOF film with highly dipolar linkers, initially reported by Hamer et al [29] A vapor-phase assisted synthetic protocol using the dicyanobenzodioxane dipolar rotor linker led to ordered peaks being observed in out-of-plane XRD scans. However, the GIWAXS data of the fabricated structure (in Figure S3, Supporting Information) do not qualitatively agree with that expected from a UiO topology; the wide array of off-axis peaks is missing.…”

Computational Study of Ground-State Destabilization Effects and Dipole–Dipole Interaction Energies in Amphidynamic Crystals

“…18 The installation of electron-withdrawing cyano substituents opposite to electron-donating benzo-1,4-dioxane (9) and benzo-1,3dioxole (10) substituents gives rise to dipole moments of 7.8 and 9.4 D, respectively (Table 1). 23 With that in mind, we decided to explore analogous molecular rotors with paradicarboxylate groups 9 and 10 in Scheme 1 in order to establish the relation between rotational barriers and their orientation-dependent dipole−dipole−dipole interactions.…”

Benzothiadiazole-based rotation and possible antipolar order in carboxylate-based metal-organic frameworks

“…1 ). The moiety can act as a rotor at certain frequencies and temperatures 19 . Moreover, applying a high electric field in principle can fix the direction of the macroscopic polarization.…”