Lanthanide Functionalized Hydrogen-bonded Organic Framework Hybrid Materials: Luminescence Responsive Sensing, Intelligent Applications and Biomimetic Design

As a distinct category of crystalline porous materials, hydrogen-bonded organic frameworks (HOFs) are assembled from organic building blocks through H-bonding and other weak intermolecular interactions, which position HOFs as a versatile platform for investigating multifunctional porous materials. Aromatic subunits existing in the majority of HOF linkers are responsible for the luminescence exhibited by HOFs upon ultraviolet excitation mostly in nature. Recently, there has been a surge of attention in utilizing luminescent functionalized HOFs for luminescence responsive sensing due to their strong fluorescence and phosphorescence emission, versatile postsynthetic functionalization property, great solution processing performance, outstanding luminescent stability and specific recognition ability, and excellent biocompatibility.

Functionalized HOFs refer to hybrid materials in which foreign functional species are incorporated into the framework of HOFs to endow specific functionalities. The presence of residual hydrogen-bonding donor/acceptor units and weak interactions such as electrostatic interactions in the HOF structures enables foreign species to bind with HOFs to fabricate functionalized HOFs. Moreover, a controllable aperture and regular pore structure can also facilitate the encapsulation of guest luminescent substances. At present, functionalized HOF materials are mainly prepared by three strategies, including ion exchange, coordination postsynthetic modification, and in situ composition. Functionalized HOFs can generate rich luminescence centers in which dual-luminescent centers (the luminescence of HOFs and foreign functionalized species) are the main types. Lanthanide functionalized HOFs (Ln@HOFs), as one of the most significant subclasses of functionalized HOFs, integrate the intrinsic photoluminescence of HOFs and the characteristic emission of Ln³⁺ ions. Ln@HOFs can exhibit sensitive luminescence changes (on, off, and ratio changes) in response to specific analytes. These characteristics have enabled functionalized HOF materials and devices to achieve the sensing of various chemical analytes and even physical stimuli.

Recent research progress is described in this Account, focusing on the use of functionalized HOF hybrid materials to generate multiple luminescent centers for various applications, including luminescence responsive sensing, intelligent applications, and biomimetic design. In consideration of functionalized HOFs for photo responsive sensing, we primarily highlight these materials used for the sensing of typical chemical analytes such as gases, organic pollutants, carcinogens, pesticides, drugs, and biomarkers, together with physical temperature. In the intelligent application section, research of HOFs in the fields of intelligent anticounterfeiting, latent fingerprint identification, smartphone recognition, intelligent logic devices, and intelligent analysis platforms are summarized. Moreover, we also investigate various biomimetic designs of functionalized HOF materials for chemical and physical stimulus sensing. In this Account, we only discuss the luminescence responsive sensing of functionalized HOFs, especially Ln@HOFs materials, while pure HOF luminescence responsive sensing is not within the scope of discussion. We hope that this Account can stimulate more innovative research to prepare advanced functionalized HOFs materials for luminescent applications.