Tunable Fluorescence in Two-Component Hydrogen-Bonded Organic Frameworks Based on Energy Transfer

Abstract

A dumbbell-shaped compound (TPAD) with four 2,4-diaminotriazine moieties as H-bond units and a benzene ring as a bridge group was found to form hydrogen-bonded organic frameworks (HOFs) with strong cyan fluorescence. An energy acceptor, 6,6′,6″, 6‴-(((benzo[c][1,2,5]thiadiazole-4,7-diylbis-(4,1phenylene))bis(azanetriyl))tetrakis(benzene-4,1-diyl))tetrakis-(1,3,5-triazine-2,4-diamine) (BTAD), with the same molecular skeleton as TPAD and a longer emission wavelength could homogeneously distribute within the framework of TPAD through occupying the locations of TPAD. As a result, two-component HOFs (TC-HOFs) were formed. The nonradiative energy transfer from TPAD as the donor to BTAD as the acceptor happens within frameworks owing to the efficient spectral overlap between the emission of TPAD and the absorption of BTAD. Moreover, the emission wavelengths and colors of TC-HOFs could be easily and continuously modulated by the content of the acceptor. The fluorescence color changed from cyan to orange when the content of BTAD gradually increased. This finding affirms that TC-HOFs with continuously adjustable composition can be constructed from two molecules with the same molecular skeleton, and highly efficient nonradiative energy transfer may happen in porous TC-HOFs. To the best of our knowledge, these TC-HOFs are the first example of TC-HOFs involved in energy transfer.

Multifunctional Porous Hydrogen-Bonded Organic Frameworks: Current Status and Future Perspectives

“…Most HOFs are composed of aromatic organic tectons with larger π-conjugated systems. Such building units usually have intrinsic photoluminescent properties, enabling HOFs with the potential as photonic materials. ,− It is worthy to note that the luminescent behavior of an HOF could be different from that of its pristine organic build blocks due to the highly ordered arrangement. Specially, HOFs’ luminescence could be responsive to the slight structural change caused by external stimulus or guest–host interactions, which could be harnessed for the luminescent sensing of the stimulus or guest molecules. − A representative example is demonstrated by the desolvated CPHATN-1a, which exhibits the reversible acid-induced luminescence change. , CPHATN-1 is built from a hexaazatrinaphthylene derivative with carboxyphenyl groups, possessing significant thermal stability up to 633 K. A strong luminescence with a maximum emission at 539 nm is observed for desolvated CPHATN-1, which turns off/on upon the reversible adsorption/desorption of HCl vapor as a result of the protonation/deprotonation of pyradyl N atoms.…”

Recent Advances in Luminescent Hydrogen‐Bonded Organic Frameworks: Structures, Photophysical Properties, Applications

“…Besides force stimuli, Xue and coworkers reported tunable fluorescence via energy transfer between two-component HOFs based on dumbbell-shaped compounds TPAD (19) and BTAD (20) (Figure 7c). [40] TPAD and BTAD crystals showed cyan and orange fluorescence with emission peaks of 500 and 610 nm, respectively. TPAD doped with different molar contents of BTAD demonstrated red-shift emission from green to yellow, then orange.…”

“…Reproduced with permission. [ 40 ] Copyright 2022, American Chemical Society. d) Molecular stacking in PCS crystal.…”

“…Photographs of TC-HOF (0 mol%), BTAD (100 mol%) and cocrystals of TC-HOF with the content of BTAD at the molar ratio of 1%, 2%, 10%. Reproduced with permission [40]. Copyright 2022, American Chemical Society.…”

A Multistimuli Responsive, Flexible Luminescent Framework and Its Applicability in Anticounterfeiting

“…Diaminotriazine (DAT) is a typical functional group for H-bonding and can form double H-bonds in the N···H–N way; thus, it has been successfully applied to construct porous HOFs in the past. − Furthermore, in addition to the N–H moieties participating in the H-bonds between the DAT groups, the voids also contain a large number of free N–H residues. These voids provide an excellent micro-environment for the formation of strong H-bonds with guests such as alcohols and water.…”