Lanthanide Functionalized Hydrogen-bonded Organic\nFramework Hybrid Materials: Luminescence Responsive Sensing, Intelligent\nApplications and Biomimetic Design

ConspectusAs a distinct\ncategory of crystalline porous materials, hydrogen-bonded\norganic frameworks (HOFs) are assembled from organic building blocks\nthrough H-bonding and other weak intermolecular interactions, which\nposition HOFs as a versatile platform for investigating multifunctional\nporous materials. Aromatic subunits existing in the majority of HOF\nlinkers are responsible for the luminescence exhibited by HOFs upon\nultraviolet excitation mostly in nature. Recently, there has been\na surge of attention in utilizing luminescent functionalized HOFs\nfor luminescence responsive sensing due to their strong fluorescence\nand phosphorescence emission, versatile postsynthetic functionalization\nproperty, great solution processing performance, outstanding luminescent\nstability and specific recognition ability, and excellent biocompatibility.Functionalized HOFs refer to hybrid materials in which foreign\nfunctional species are incorporated into the framework of HOFs to\nendow specific functionalities. The presence of residual hydrogen-bonding\ndonor/acceptor units and weak interactions such as electrostatic interactions\nin the HOF structures enables foreign species to bind with HOFs to\nfabricate functionalized HOFs. Moreover, a controllable aperture and\nregular pore structure can also facilitate the encapsulation of guest\nluminescent substances. At present, functionalized HOF materials are\nmainly prepared by three strategies, including ion exchange, coordination\npostsynthetic modification, and in situ composition. Functionalized\nHOFs can generate rich luminescence centers in which dual-luminescent\ncenters (the luminescence of HOFs and foreign functionalized species)\nare the main types. Lanthanide functionalized HOFs (Ln@HOFs), as one\nof the most significant subclasses of functionalized HOFs, integrate\nthe intrinsic photoluminescence of HOFs and the characteristic emission\nof Ln<sup>3+</sup> ions. Ln@HOFs can exhibit sensitive luminescence\nchanges (on, off, and ratio changes) in response to specific analytes.\nThese characteristics have enabled functionalized HOF materials and\ndevices to achieve the sensing of various chemical analytes and even\nphysical stimuli.Recent research progress is described in this\nAccount, focusing\non the use of functionalized HOF hybrid materials to generate multiple\nluminescent centers for various applications, including luminescence\nresponsive sensing, intelligent applications, and biomimetic design.\nIn consideration of functionalized HOFs for photo responsive sensing,\nwe primarily highlight these materials used for the sensing of typical\nchemical analytes such as gases, organic pollutants, carcinogens,\npesticides, drugs, and biomarkers, together with physical temperature.\nIn the intelligent application section, research of HOFs in the fields\nof intelligent anticounterfeiting, latent fingerprint identification,\nsmartphone recognition, intelligent logic devices, and intelligent\nanalysis platforms are summarized. Moreover, we also investigate various\nbiomimetic designs of functionalized HOF materials for chemical and\nphysical stimulus sensing. In this Account, we only discuss the luminescence\nresponsive sensing of functionalized HOFs, especially Ln@HOFs materials,\nwhile pure HOF luminescence responsive sensing is not within the scope\nof discussion. We hope that this Account can stimulate more innovative\nresearch to prepare advanced functionalized HOFs materials for luminescent\napplications.