Precise Design and Deliberate Tuning of Turn-On Fluorescence in Tetraphenylpyrazine-Based Metal−Organic Frameworks

Abstract

The manipulation on turn-on fluorescence in solid state materials attracts increasing interests owing to their widespread applications. Herein we report how the nonradiative pathways of tetraphenylpyrazine (TPP) units in metal−organic frameworks (MOFs) systems could be hindered through a topological design approach. Two MOFs single crystals of different topology were constructed via the solvothermal reaction of a TPP-based 4,4′,4″,4‴-(pyrazine-2,3,5,6-tetrayl) tetrabenzoic acid (H4TCPP) ligand and metal cations, and their mechanisms of formation have been explored. Compared with the innate low-frequency vibrational modes of flu net Tb-TCPP-1, such as phenyl ring torsions and pyrazine twists, Tb-TCPP-2 adopts a shp net, so the dihedral angle of pyrazine ring and phenyl arms is larger, and the center pyrazine ring in TPP unit is coplanar, which hinders the radiationless decay of TPP moieties in Tb-TCPP-2. Thereby Tb-TCPP-2 exhibits a larger blue-shifted fluorescence and a higher fluorescence quantum yield than Tb-TCPP-1, which is consistent with the reduced nonradiative pathways. Furthermore, Density functional theory (DFT) studies also confirmed aforementioned tunable turn-on fluorescence mechanism. Our work constructed TPP-type MOFs based on a deliberately topological design approach, and the precise design of turn-on fluorescence holds promise as a strategy for controlling nonradiative pathways.

Two Chemorobust Cobalt(II) Organic Frameworks as High Sensitivity and Selectivity Sensors for Efficient Detection of 3-Nitrotyrosine Biomarker in Serum

“…It is worth mentioning that the gradient titrations are accompanied by the red-shift of emission peaks, which are mainly due to the fluorescence resonance energy transfer (FRET), 42 . 43 ) for UIO-66, comparable to or even superior to some reported MOFs 19−21 (Table 1). And the recyclability results in Figure 6d and Figure 7d showed that the detectability of two CoMOFs can be maintained well at least for five cycles.…”

“…As expected, the continuous addition of 3-NT caused the luminescence intensities of three water-stable MOFs to be reduced ceaselessly (Figure a, Figure a, and Figure S19a), with the CIE ranging from (0.19, 0.26) to (0.26, 0.45) for CoMOF-1 (Figure b) and (0.21, 0.22) to (0.26, 0.40) for CoMOF-2 (Figure b). It is worth mentioning that the gradient titrations are accompanied by the red-shift of emission peaks, which are mainly due to the fluorescence resonance energy transfer (FRET), . To reveal the intrinsic relationships between the luminescence intensities of the PBS suspensions of two CoMOFs and UIO-66 and the added 3-NT concentrations, the plots of I 0 / I versus [3-NT] are given in Figure c, Figure c, and Figure S19b (here I 0 and I corresponding to the luminescence intensity of the suspensions of MOFs before and after adding 3-NT).…”

Guest Encapsulation in Metal–Organic Frameworks for Photonics

“…For instance, overcoming the ACQ effect and introducing the FRET effect by inclusion of photonic guests in MOFs, due to their limited applications and high emissivity in solution, photonic guests exhibit almost quenched luminescence in the solid state when the molecules are aggregated, hence the development of photonic materials has thus been severely constrained by the ACQ effect. 35 As for MOF⊃guests composites, the pore confinement and isolation of guest species within MOFs significantly restricted the intramolecular torsional motion and restrained π−π interactions of guests, thus diminishing the ACQ effect and leading to a significant PLQY enhancement of guests. Another example is that the photonic guests are not stable in air atmosphere or extreme environments, which has severely limited their practical applications.…”

“…In addition to the aforementioned, the synergistic effect between the inherent properties of the individual photonic unit of guests and MOFs, the photonic functionality of MOF⊃guests composites can be further enhanced and optimized due to the fact that the pore microenvironment of MOFs provides an excellent platform for regulating and enhancing the photonic functionality of guest molecules. For instance, overcoming the ACQ effect and introducing the FRET effect by inclusion of photonic guests in MOFs, due to their limited applications and high emissivity in solution, photonic guests exhibit almost quenched luminescence in the solid state when the molecules are aggregated, hence the development of photonic materials has thus been severely constrained by the ACQ effect . As for MOF⊃guests composites, the pore confinement and isolation of guest species within MOFs significantly restricted the intramolecular torsional motion and restrained π–π interactions of guests, thus diminishing the ACQ effect and leading to a significant PLQY enhancement of guests.…”

Photo‐Stimuli‐Responsive Dual‐Emitting Luminescence of a Spiropyran‐Encapsulating Metal–Organic Framework for Dynamic Information Encryption

“…[18,[24][25][26][27] As an excellent luminescent material, metal-organic frameworks (MOFs) have attracted great interest due to their permanent porosity and multiple emission centers. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] Such characteristics make MOFs very promising for solid-state photoresponsive materials to address the above issue. First, incorporating photochromic molecules into the pores of MOFs can provide sufficient conformational freedom to achieve efficient photoisomerization.…”