Linkages Make a Difference in the Photoluminescence of Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) with structural designability and tunability of photophysical properties enable them to be a promising class of organic luminescent materials by incorporating well‐designed fluorescent units directly into the periodic skeletons. The photophysical properties of COFs are mainly affected by the structural parameters, which determine the conjugation degree, charge delocalization ability, and exciton dynamics of COFs. To understand the relationship between COF structures and their photophysical properties, two COFs with the same pyrene chromophore units but different linkages (imine or vinyl) were designed and synthesized. Interestingly, different linkages endow COFs with huge differences in solid‐state photoluminescence quantum yield (PLQY) for imine‐ and vinylene‐linked pyrene‐based COFs, which possess PLQY values of 0.34% and 15.43%, respectively. The femtosecond‐transient absorption spectra and time‐dependent density functional theory reveal the different charge‐transfer pathways in imine‐ and vinylene‐linked COFs, which influence the exciton relaxation way and fluorescence intensity. In addition, an effective white‐light device was obtained by coating the vinylene‐linked COF on a light‐emitting diode strip.

Covalent Organic Framework-Based Photocatalyst for Activation of Peroxymonosulfate: Implications for Degradation of Organic Pollutants

“…The weak fluorescence of TFPT-TAPB COF was attributed to the reduced π-conjugation of the imine linkage along with the nonradiative relaxation caused by the internal rotation of the imine bond . Moreover, according to the TCSPC analysis, the TFPT-TCPB COF-COOH exhibited the largest PL lifetime, indicating the lowest rate of photogenerated electron–hole recombination and the best electron–hole separation ability (Figure F) …”

Construction of Layer-Blocked Covalent Organic Framework Heterogenous Films via Surface-Initiated Polycondensations with Strongly Enhanced Photocatalytic Properties

“…Covalent organic frameworks (COFs) are crystalline porous polymers that can polymerize organic building blocks into extended network by covalent linkages, − featuring well-defined extended framework, tunable functionalization and permanent porosity. , Since the seminal progress reported by Yaghi et al in 2005, various dynamic linkages with different reversibility, chemical stability and electron arrangement have been developed such as borate esters, imines, − triazines , and vinylene etc. − Among them, the imine-linked COFs usually possess high crystallinity and porosity, − but the hydrolysis and polarization of imine linkages limit the stability and charge carrier mobility. In another scenario, the vinyl-linked COFs exhibit excellent semiconducting property and stability due to its fully π-conjugated structures, , providing superior performance for photocatalysis, − photoluminescence − and fluorescence detection …”

Regulating Donor–Acceptor Interactions within 2-Methylpyridine-Mediated Vinylene-Linked Covalent–Organic Frameworks for Enhanced Photocatalysis

“…These materials exhibit a plethora of intriguing properties, including well-defined pore structures, facile functionalization, and structural diversity, rendering them highly promising for various domains, such as adsorption , and separation, − biomedicine, − energy conversion, − sensing, − and catalysis. − Of particular interest are vinylene-linked COFs, which have garnered considerable attention due to their remarkable stability and pronounced π-electronic communication, rendering them highly prospective for photocatalysis . Nevertheless, in comparison to these COFs based on boroxine linkage, imine linkage, azine linkage or imide linkage, the construction of vinylene-linked COFs remains in an infant stage and challenging, limiting to a few kinds of monomers, including phenylacetonitrile derivatives, 2,4,6-trimethylpyridine, , tricyanomesitylene, 2,4,6-trimethyl-1,3,5-triazine, , 2,4,6-trimethylpyrylium tetrafluoroborate, 2,5-dimethylpyrazine, , benzoxazole derivatives, 2,2′,6,6′-tetramethyl-4,4′-bipyridine, phosphorus ylide derivatives, etc. However, synthesizing these monomers often involves intricate processes and even the utilization of toxic raw materials.…”

“…26−38 Of particular interest are vinylene-linked COFs, which have garnered considerable attention due to their remarkable stability and pronounced π-electronic communication, rendering them highly prospective for photocatalysis. 39 linkage, azine linkage or imide linkage, the construction of vinylene-linked COFs remains in an infant stage and challenging, limiting to a few kinds of monomers, including phenylacetonitrile derivatives, 40 2,4,6-trimethylpyridine, 34,41 tricyanomesitylene, 27 2,4,6-trimethyl-1,3,5-triazine, 42,43 2,4,6trimethylpyrylium tetrafluoroborate, 28 2,5-dimethylpyrazine, 44,45 benzoxazole derivatives, 33 2,2′,6,6′-tetramethyl-4,4′bipyridine, 26 phosphorus ylide derivatives, 46 etc. However, synthesizing these monomers often involves intricate processes and even the utilization of toxic raw materials.…”