Rare-earth-based donor–acceptor metal–organic frameworks with low thermal quenching and dual emission mechanisms for high-temperature sensing

Abstract

Rare-earth-based metal–organic frameworks (RE-MOFs) hold significant promise for temperature sensing applications but face challenges due to the common thermal quenching (TQ) effect. In this study to address this limitation, we designed and synthesized a novel class of RE-based donor–acceptor MOFs (RE-DA-MOFs, termed DZU-500⊃PAH) with enhanced thermal stability and highly tunable luminescence, via integrating a phenazine-based electron-deficient ligand (dppz), RE ions (Eu³⁺, Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺), and polycyclic aromatic hydrocarbon (PAH) guests. Due to their host–guest architectures that are stabilized by the hydrogen bonds among the triple-fold metal chain structures and π–π stacking interactions between the donor and acceptor units, non-radiative decay of the framework can be effectively suppressed at elevated temperatures. Thus, these RE-DA-MOFs exhibit TQ-resistant through-space charge transfer (TSCT) fluorescence properties (298–473 K), which can be well modulated in the visible light range (493–584 nm) through the changing of PAH molecules. Specifically, the Eu³⁺-based MOFs, [DZU-500(Eu)⊃PAH], not only display TSCT-based emission that is TQ-resistant, but also exhibit characteristic Eu³⁺-centered emission that is TQ-sensitive. Through the difference of the dual emission mechanisms, DZU-500(Eu)⊃PAH can be used as both intensity-ratiometric and colorimetric high-temperature sensing materials. Firstly, the intensity ratio of Eu³⁺- and TSCT-based emission peaks exhibited good polynomial relationships with increasing temperature. Furthermore, by selecting an appropriate PAH guest as the donor, reversible color changes (red to green) in response to temperature variations can be observed in the corresponding MOF. These results highlight the potential of RE-DA-MOFs as low thermal-quenching materials and high-temperature fluorescent thermometers.

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New concepts

Rare-earth-based metal–organic frameworks (RE-MOFs), derived from the coordination of organic ligands and RE ions, exhibit particular promise as fluorescent temperature sensors. However, most reported RE-MOF-based sensors suffer severe signal attenuation due to thermal quenching (TQ) effects at elevated temperatures (373–473 K). Besides, overcoming TQ while maintaining stimulus responsiveness remains a critical challenge. This study introduces a novel strategy to address this issue, through the construction of RE-based donor–acceptor MOFs (RE-DA-MOFs) by integrating rigid donor–acceptor (D–A) π–π stacking and stabilized RE-coordination chains into a host–guest framework. In particular, the obtained Eu-DA-MOFs exhibit dual-emission mechanisms: (1) through-space charge transfer (TSCT) fluorescence emission derived from the charge transfer between the D–A components, which is TQ-resistant from 298 to 473 K and highly tunable in the visible light range (493–584 nm); (2) the characteristic emission of Eu³⁺ ions derived from the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ energy level transition, which is TQ-sensitive. The two kinds of distinct emission mechanisms endow the Eu-DA-MOFs with dual-mode functions of both intensity-ratiometric and colorimetric high-temperature sensing. Our present work shows how to design RE-DA-MOFs realizing synergistically TQ-resistance and high-temperature sensing.

1. Introduction

Metal–organic frameworks (MOFs), as a class of crystalline materials, have emerged as promising candidates for applications in gas adsorption/separation, catalysis, and chemical sensing due to their unique combination of inorganic–organic hybrid structures, tunable porosity, and high pore volumes.^1–9 Among these, rare-earth MOFs (RE-MOFs), which employ rare-earth ions as metal centers, exhibit narrow emission bandwidths, long fluorescence lifetimes, and broad light absorption ranges, making them indispensable in optical lighting, anti-counterfeiting, information encryption, and environmental monitoring.^10–18 In the realm of temperature sensing, RE-MOFs show particular promise as ratiometric fluorescent sensors due to the multi-emission peaks of rare-earth ions. This intrinsic property enables self-referencing measurements, significantly improving accuracy by compensating for environmental interference. The characteristic emission peaks of a single rare-earth ion correspond to transitions from independent excited states that typically exhibit similar thermal responses. Consequently, multiple emission peaks from a MOF doped with only one type of rare-earth ion (e.g., only Eu³⁺ or Tb³⁺) are generally unsuitable for constructing ratiometric fluorescent thermometers. A common strategy involves co-doping MOFs with different rare-earth ions (most frequently combining Eu³⁺ and Tb³⁺), or incorporating an additional luminescent organic moiety into the RE-MOF structure, creating a dual-emitting system.^19–22 In these approaches, under sensitization by the organic ligands, the ratio of characteristic emission intensities of different emitters (for example, the intensity ratio between Eu at 613 nm and Tb at 545 nm, or the intensity ratio from the organic moiety and the RE ions), would exhibit a strong, measurable dependence on temperature, enabling fluorescent temperature sensing.

However, most reported RE-MOF-based sensors operate effectively only at/below room temperature. At elevated temperatures (373–473 K), severe signal attenuation occurs due to thermal quenching (TQ) effects, resulting in diminished sensitivity and reliability.^23–32 Recent advances have proposed strategies to counteract TQ, such as Huang and coworkers’ demonstration of negative thermal expansion (NTE)-mediated luminescence enhancement in MOFs.^33–35 In another example, Ma and coworkers developed a cadmium halide-acridine (AD) MOF that retains 84% of its initial emission intensity at 423 K, attributed to the alternating arrangement of CdCl₂ inorganic chains (donors) and delocalized AD π-conjugated systems (acceptors) stabilized by strong coordination bonds and π–π stacking interactions.³⁶ This proved that the introduction of donor–acceptor (D–A) systems and rational modulation of structural rigidity can enhance intermolecular π–π stacking and charge-transfer interactions, thereby improving both thermal stability and luminescent performance. Despite these advances, achieving thermal stability often compromises stimulus-responsive behavior, a critical requirement for dynamic sensing. Thus, there remains an urgent need to develop RE-MOFs that synergistically integrate TQ resistance with stimulus-responsive luminescence.

Based on the above analysis, we propose the design of rare-earth-based donor–acceptor MOFs (RE-DA-MOFs) to develop low-TQ luminescent materials for high-temperature sensing (Scheme 1).^35–39 Our prior studies have demonstrated the successful construction of highly tunable DA-MOFs by designing electron-deficient framework acceptors to encapsulate electron-rich guests through coordination-driven self-assembly and host–guest interactions.^40–43 The innovation of this work lies in three key aspects: (1) exploiting the high coordination numbers of rare-earth ions combined with strong D–A π–π interactions to stabilize the framework structure; (2) establishing a dual-emission mechanism integrating D–A charge-transfer luminescence with RE-centered emissions; and (3) leveraging the TQ-resistant D–A luminescence and TQ-sensitive rare-earth emissions to achieve chromaticity-based high-temperature sensing.

Scheme 1 Schematic illustration of the strategy for the construction of RE-DA-MOFs utilizing host–guest chemistry.

In this study, we designed a novel host RE-MOF system (DZU-500) using electron-deficient dipyrido[3,2-a:2′,3′-c]phenazine (dppz, acceptor), terephthalic acid (PTA, linker), and rare-earth ions (Eu³⁺, Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺). Through a one-pot synthesis to achieve encapsulated diverse polycyclic aromatic hydrocarbon (PAH) guests (donors), a series of RE-DA-MOFs (DZU-500⊃PAH) were successfully synthesized with highly tunable luminescence. Thermogravimetric analysis (TGA) and variable-temperature PXRD confirmed their exceptional thermal stability, attributed to the enhanced framework rigidity from triple-fold coordination chains and densely packed D–A structures. Among these materials, DZU-500(Eu)⊃PAH [PAH = triphenylene (1), phenanthrene (2), pyrene (3), anthracene (4)] exhibits dual emission mechanisms: (1) through-space charge transfer (TSCT) from the D–A structure, and (2) characteristic multi-emission peaks from Eu³⁺ ions. Critically, the TSCT emission displays minimal TQ due to robust D–A stacking, while the Eu³⁺-based emissions exhibit conventional TQ. This divergent temperature-dependent behavior enables DZU-500(Eu)@PAH to achieve superior chromaticity-based high-temperature sensing properties.

2. Results and discussion

2.1. Structural analysis

Due to their iso-structural characteristics confirmed from PXRD patterns (Fig. S1, ESI†), DZU-500(Eu)⊃pyrene (3) with high quality single crystals is selected here as a typical representative for the description. Single crystal X-ray diffraction analysis shows that compound 3 belongs to the triclinic crystal system with a space group of P1̄. As shown in Fig. S2a (ESI†), in its asymmetric unit, there exists one crystallographic independent Eu³⁺ ion, one dppz ligand, one and a half PTA²⁻ ligands, one coordinated water molecule, and half a pyrene molecule. Eu1 adopts an eight-coordinated dodecahedral geometric configuration with five carboxyl oxygen atoms from four different PTA²⁻ ligands, two pyridine nitrogen atoms from one dppz ligand, and one water molecule. It is worth noting that two adjacent Eu³⁺ ions are bonded by two carboxyl groups of two PTA²⁻-1 ligands with a coordination mode of μ₂-η¹:η¹ to form a binuclear cluster, while the carboxyl groups of PTA²⁻-2 use two different modes of η¹ and η² connecting the Eu₂ clusters (Fig. 1a). Therefore, a triple-fold one-dimensional (1D) chain-like structure is formed extending along the b-axis through the connection of Eu₂ clusters with a group of PTA²⁻ ligand (including one PTA²⁻-1 and two PTA²⁻-2). Subsequently, the dppz ligands are inlaid in the 1D chains to form a parallel arrangement by chelating coordination with Eu³⁺ ions (Fig. 1b). Importantly, hydrogen bonds (OH⋯O4: 1.830 Å; OH⋯O6: 2.059 Å) are formed between the carboxylic oxygen atoms of PTA²⁻-2 from each chain and coordinated H₂O atoms from adjacent chains (Fig. S2b, ESI†).

Fig. 1 (a) Formation of the triple-fold 1D chain structure through the connection of PTA²⁻ ligands with the Eu₂ clusters; (b) formation of the chain structure with the inlaid dppz ligands; (c) formation of the coordination spaces through the adjacent chains insertion; (d) the final packing structures with ⋯AADAAD⋯ arrangement along the b-axis; (e) the pyrene encapsulated electron-deficient coordination space formed by four dppz ligands from two adjacent chain structures.

Furthermore, the dppz ligands from adjacent chains show in-pair π–π stacking interactions. Therefore, the dppz embedded chain structures are inserted together, generating a 3D supramolecular framework with electron-deficient coordination spaces which allow the encapsulation of planar electron-rich guests (Fig. 1c and d). Moreover, each space in compound 3 contains one free pyrene molecule, forming the close π–π stacking with ⋯AADAAD⋯ arrangement along the b-axis (Fig. 1e).

2.2. Phase purity and thermal stability analysis

Powder X-ray diffraction (PXRD) and thermogravimetric (TG) experiments were carried out in order to examine the purity and stability of these materials. As shown in Fig. S3 (ESI†), the main peaks of the synthesized samples of the four Eu-DA-MOFs all match well with the simulated one of compound 3 obtained from SCXRD diffraction data, indicating compounds 1, 2 and 4 have similar coordination networks with compound 3, and all products have good phase purity and crystallinity.

TGA analysis on these Eu-DA-MOFs is shown in Fig. S4 (ESI†). These Eu-DA-MOFs underwent two main stages of weight loss on the TGA curves: the first small weight loss occurred in the temperature range of 192–234 °C, corresponding to the departure of coordination water molecules (for example, in compound 3, the experimental loss of 2.2% agrees well with the calculated loss of 2.3%); the second stage begins after 450 °C, demonstrating the decomposition of frameworks. The results indicate that different guests do not significantly affect the thermal stability of the frameworks. Meanwhile, these PAH molecules that are prone to sublimation are well preserved and quickly leave as the framework decomposed. The high thermal stability of these frameworks was further confirmed by the variable-temperature PXRD experiments (Fig. S5, ESI†), which reveal that the frameworks are still stable with high crystallinity even under 623 K. The high thermal stability could be attributed to the strong π–π interactions between D and A building blocks inside these host–guest CPs, as well as the special chain structures of DZU-500.

2.3. Photophysical properties

Due to the antenna effect of ligands, luminescence based on the Eu³⁺ ions can be excited. More importantly, benefiting from the triple-fold 1D chain-like structure to accommodate varied PAH guests, the guest-dependent TSCT interactions and luminescence can be further modulated. Therefore, these materials must present two kinds of luminescence with different mechanisms. Based on the above analysis, the photophysical properties of these Eu-DA-MOFs were systematically investigated to explore their potential applications in luminophores.

First, the absorption and luminescent spectra of the Eu³⁺ based Eu-DA-MOFs were firstly tested to verify the occurrence of TSCT interactions (Fig. S6, ESI† and Fig. 2b). Compared with the corresponding guest molecules and dppz ligand, the absorption spectra of the Eu-DA-MOFs exhibit new broad absorption bands in the visible light region (>400 nm), which is related to intermolecular TSCT between the dppz ligands and corresponding guest molecules. Different luminescent spectra were also found and the Eu-DA-MOFs exhibit broad, feature-less emission bands with peaks ranging from 493 to 584 nm. In addition, the large Stokes shifts between the absorption spectra and luminescent spectra of the Eu-DA-MOFs also indicate an efficient TSCT process of the exciplex composed of the dppz ligand and corresponding PAH guests. Second, the Eu-DA-MOFs also show the characteristic emission peaks of Eu³⁺ around 593 nm and 618 nm, which respectively represent the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ energy level transition. Based on the guest-dependent TSCT interactions and Eu³⁺ based frameworks, these MOFs reveal a wide range of emission colors from green to orange, as seen from the luminescent spectra and the coordinates in the Commission International de L’Eclairage (CIE) chromaticity diagram (Fig. 2a, c and Table. S1, ESI†). This demonstrates the luminescent properties of these MOFs can be modulated by encapsulation of different PAH guests.

Fig. 2 Photophysical properties of DZU-500(Eu)⊃guests: (a) luminescence microscopy images; (b) normalized emission spectra; (c) the CIE coordinates.

To better comprehend if the emission behaviors of these Eu-DA-MOFs could be directionally regulated, the relationship between the guest molecules and the TSCT-based emission maxima were investigated. It revealed a good linear fit between the ionization potentials (IP) and the emission maxima (Fig. S7, ESI†), which is just observed in a few luminescent MOFs and cocrystal systems. These rules allow us to modulate the emission behaviors of these Eu-DA-MOFs by selecting guests with appropriate IPs and molecular structures.

Additionally, due to the presence of two luminescent sources, the fluorescence lifetimes (τ) of the Eu-DA-MOFs were further measured using different emission peaks. As shown in Fig. S8 and Table S1 (ESI†), the τ values corresponding to both the TSCT-based emission peaks and the characteristic emission peaks of Eu³⁺ are in the microsecond range (τ_TSCT: 3.07–5.65 μs; τ_{614 nm}: 18.01–87.65 μs); among them, DZU-500(Eu)⊃anthracene (4) exhibits the highest value of 87.65 μs. Moreover, the absolute quantum yields (Φ) of these Eu-DA-MOFs were characterized in the range of 0.72–2.52% (Table S1, ESI†).

2.4. Variable-temperature fluorescence

Due to their very high thermal stability and tunable luminescence, the thermal-stimuli-responsive properties of Eu-DA-MOFs were characterized using variable temperature fluorescence spectra. Taking compound 3 as an example, it is very interestingly found that fluorescence intensity of the TSCT based emission peak at 560 nm almost has no decrease from room temperature (RT) to 373 K, and there is still 92% of the intensity of RT even under 433 K. When it comes to 477 K, the intensity declined to 64% of the original intensity. Besides, it showed a common decreasing trend for the emission peaks of Eu³⁺ ions. Obviously, the TSCT based fluorescence of these Eu-DA-MOFs exhibits low thermal quenching behavior, which is very useful and beneficial for applications under high temperature environments. In order to investigate the possible reasons for their thermal quenching resistance, SCXRD analysis of compound 3 was carried out under different temperatures. The results reveal that the cell volume only shows little enhancement of 30.68 ų from RT to 423 K (Table 1). In detail, the b axis that directly reflects the extension direction of the π–π stacking of D and A components exhibits the smallest length increase of only 0.0323 Å with temperature raised to 423 K. As for the a axis, the length exhibits a slightly larger increase of 0.0573 Å from 298 to 373 K. Furthermore, although the overall length of the c axis shows an upward trend with the largest increase of 0.1338 Å, it experiences a process of first rising from 298 to 373 K and then falling from 373 K to 423 K. This length change is in accordance with the fluorescence intensity change of TSCT-based emission in the range of 298–423 K in that the intensity increases first and then decreases. Overall, minor changes of the cell parameters lead to the minimal changes in distances and overlaps between the D and A components. This indicates that the enhanced framework rigidity by the strong ⋯AADAAD⋯ π–π interactions and the triple-fold chain structures could effectively limit the thermal motion of molecules in the whole framework, in order to significantly reduce the non-radiative decays with increasing temperature. In addition, the distances between O atoms that participate in the formation of hydrogen bonds in compound 3 just present slight changes under temperatures from RT to 423 K, further indicating the high thermal stability of the whole framework. Therefore, compound 3 can present TSCT-based fluorescence with low thermal quenching under temperature ranges of 298–423 K. Continuously increasing the temperature over 473 K, coordinated H₂O molecules began to leave with the gradual exposure of unsaturated metal sites, and the hydrogen bonds among the chains were thus broken down (Fig. 4a). When the temperature increased to 573 K, open metal centers were fully exposed with adjacent chains in the appropriate positions, and the carboxyl oxygen atoms in η¹ coordination mode from PTA²⁻-2 ligands in one chain changed to the chelate-bridge coordination mode connecting another adjacent chain. Thus, the binuclear clusters in the original structures are linked to form metal chain structures, and the 1D chain structure finally converts into a 2D layer stacking structure (Fig. 4b). As the phase transition occurs, the fluorescence intensity quenches at a slightly larger level.

Table 1 Crystal data comparison of compound 3 under different temperatures

	a (Å)	b (Å)	c (Å)	V (Å^3)	d1 (Å)	d2 (Å)
a The crystal data was collected under the RT, 373 K and 423 K directly.b The crystal data was collected under RT, by using the samples after treatment at 573 K for two hours.
^aRT	9.6484	10.2129	16.1553	1488.72	2.625	2.785
^a373 K	9.6830	10.2240	16.2950	1510.40	2.630	2.801
^a423 K	9.7057	10.2452	16.2891	1519.40	2.648	2.818
^b573 K	9.6120	10.2200	15.8600	1439.91	—	—

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Fig. 3 Variable-temperature solid-state emission spectra, CIE coordinates and normalized intensity of (a)–(c) compound 3 and (d)–(f) compound 1 excited by 380 nm UV irradiation.

Fig. 4 Structures of compound 3 obtained from SCXRD analysis under different temperatures. (a) Formation of the metal chains (573 K) by the removal of coordinated H₂O molecules in the original binuclear clusters (d₁ and d₂ represent the distances between O atoms that participate in the formation of hydrogen bonds); (b) the hydrogen bonds destruction in the crystal transformation process from RT to 573 K; (c) the final host–guest frameworks of compound 3 with no significant changes under RT, 373 K and 423 K; (d) the host–guest framework of compound 3 after treatment at 573 K formed by pyrene molecules encapsulated in the coordination spaces between the 2D layers.

For comparison, RE-DA-MOFs based on other rare earth metal ions (Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺) were also synthesized by using pyrene as guest donors. However, they only present the TSCT-based luminescence, and the characteristic emission peaks of the metal ions could not be excited under 365 nm (Fig. 5a). The main reasons might be as follows: (1) in the Tb³⁺-MOF, the characteristic emission peaks of Tb³⁺ ions require higher excitation energy to become observable, and upon 264 nm excitation, the dominant emission peaks at 494 nm (⁵D₄ → ⁷F₆), 547 nm (⁵D₄ → ⁷F₅), 584 nm (⁵D₄ → ⁷F₄), and 621 nm (⁵D₄ → ⁷F₃) emerge prominently in DZU-500(Tb)⊃pyrene (Fig. S10a and b, ESI†). (2) TSCT-based fluorescence from the D–A units exhibits a strong and broad emission band, which obscured the relatively weak emission peaks of Sm³⁺ and Dy³⁺ ions. To avoid this situation, TSCT-based emission should be tuned by modulating the guests to shift its spectral position away from the characteristic emission regions of the RE ions, thereby minimizing spectral overlap (Fig. S10c and d, ESI†). (3) As for Gd³⁺, its characteristic emission peaks are not within the range of the visible light region, and due to the poor matching between the energy of the T₁ state of the TPA ligand (23 923) cm⁻¹ and the energy level of Gd³⁺ ions (32 500 cm⁻¹), only the TSCT-based emission peak is visible in the fluorescence spectra of the Gd-MOF.

Fig. 5 Solid-state emission spectra for (a) DZU-500(M)⊃pyrene, and (b) DZU-500(Tb)⊃guests; (c) normalized variable-temperature solid-state emission spectra of DZU-500(Dy)⊃pyrene. The relationship between the Eu³⁺-based emission intensity and temperature for (d) compound 3 and (e) compound 1.

Nevertheless, the TSCT-based luminescent properties can also be well tuned in the visible light region by regulation of the guest molecules in the other RE-DA-MOFs, such as DZU-500(Tb)⊃guests (Fig. 5b). Moreover, their TSCT-based fluorescence intensity, such as DZU-500(Dy)⊃pyrene (Fig. 5c), exhibits similar temperature resistance as the DZU-500(Eu)⊃pyrene, further indicating the effectiveness of our strategy for the design of low thermal quenching fluorescence materials.

2.5. High-temperature sensing

Due to the low TQ of TSCT-based fluorescence and the high TQ of the Eu³⁺-based fluorescence, these Eu-DA-MOFs can be used as both intensity-ratiometric and colorimetric high-temperature sensing materials. First, the intensity ratio of Eu³⁺- and TSCT-based emission peaks exhibited good polynomial relationships with temperature increasing and colorimetric high- temperature sensing materials. First, through fitting the data between the intensity ratio of emission peaks (612 nm and 568 nm/484 nm) and temperature (298–473 K), compounds 3 and 1 both show good polynomial relationships with an equation of y = 2 × 10⁻⁵x² − 0.0153x + 4.0793 (R² = 0.9822) for compound 3 and y = −3 × 10⁻⁶x³ + 0.0036x² − 1.5241x + 221.27 (R² = 0.9943) for compound 1. Based on the equations, the relative thermal sensitivity (S_r) was further calculated for compounds 3 and 1. The results reveal that the highest value of S_r(3) is 0.275% at 473 K, while the highest value of S_r(1) is 23.91% at 313 K.

Second, as for colorimetric sensing, the design principles are as follows: the whole luminescence could be maintained in a relatively high level of intensity by the TSCT-based fluorescence under high temperature; meanwhile the luminescence color can be changeable with the intensity decrease of the Eu³⁺-based fluorescence. Therefore, changing the emitting colors into color channel ratio (R/G) data, a relationship diagram can be obtained between the R/G and temperature. With this in mind, luminescent membranes were further prepared by including DZU-500(Eu)⊃guest into polyacrylonitrile (PAN) with the help of electrospinning technology, and the DZU-500(Eu)⊃triphenylene included PAN membrane was taken as an example for the sensing application because of its clearly isolated TSCT- and Eu³⁺-based fluorescence peaks (Fig. 3). As shown in Fig. 6, the membrane exhibits a reversible fluorescence change from rose-red to green in the temperature range of 298 to 433 K. Concurrently, the R/G data present a good linear relationship (y = −0.00619x + 3.0611, R² = 0.9442) with the temperatures. The above studies indicate the potential application of the Eu-DA-MOFs here as visualizing high-temperature fluorescence thermometer, as well as the rationality of our design principles.

Fig. 6 (a) Temperature sensing of the membrane; (b) plot of the membrane color under UV light versus temperatures.

3. Conclusion

In summary, we have successfully developed thermally stable RE-DA-MOFs (DZU-500⊃PAH) by synergizing RE ions, electron-deficient dppz ligands, and PAH guests. Structural analysis demonstrates the stabilized host–guest architectures of DZU-500⊃PAH by the strong hydrogen bonds among the triple-fold coordination chains and dense D–A π–π stacking, which are confirmed using variable-temperature SC/PXRD and TGA experiments. Through the facile modulation of PAH guest molecules, the TSCT-based emission properties of DZU-500⊃PAH can be well tuned in the visible light range, which feature TQ-resistant fluorescence from 298 to 473 K. In particular, DZU-500(Eu)⊃PAH presents a dual-emission mechanism—combining TQ-resistant TSCT emission and TQ-sensitive Eu³⁺ transitions—facilitating both intensity-ratiometric and colorimetric high-temperature sensing materials. On one hand, the intensity ratio of Eu³⁺- and TSCT-based emission peaks of DZU-500(Eu)⊃pyrene/triphenylene (compounds 3 and 1) exhibits good polynomial relationships with temperature increasing from 298 to 373 K. One the other hand, the electrospun membrane containing compound 3 demonstrates the reversible fluorescence color changes with a linear R/G ratio-temperature relationship (298–433 K), highlighting practical applicability. This work advances the molecular design of RE-DA-MOFs, not only offering a robust strategy to overcome thermal quenching limitations, but also expanding their utility in high-temperature environments, such as industrial monitoring and anti-counterfeiting technologies.

Author contributions

Da-Shuai Zhang: writing – review & editing, writing – original draft, funding acquisition, conceptualization. Zhen-Wei Zhang: software, methodology, investigation, data curation. Wei Wang: investigation, data curation. Xiao-Ting Liu: writing – review & editing. Qiang Gao: software, formal analysis. Jingjing Pang: methodology, investigation. Yong-Zheng Zhang: methodology. Longlong Geng: formal analysis. Chuanqi Feng: data curation. Yanyan Gao: methodology. Sha Sha: methodology. Bin Li: formal analysis. Ai-Yun Ni: formal analysis. Xiuling Zhang: supervision. Hui Hu: writing – review & editing, software, conceptualization. Ze Chang: writing – review & editing, conceptualization.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the ESI.† Crystallographic data for [DZU-500(M)⊃pyrene, M = Sm, Eu, Gd, Tb, Dy] have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under 2442522–2442529 and can be obtained from https://www.ccdc.cam.ac.uk/.

Acknowledgements

This work was supported by Qingchuang Talents Induction Program of Shandong Higher Education Institution, the National Natural Science Foundation of China (NSFC, No. 22405032, 22375104, 22201257, 21902022, 21601028), the Natural Science Foundation of Shandong Province (No. ZR2024MB116, ZR2024QB308, ZR2023QE104, ZR2022QE025, ZR2022QB058, ZR2019QB026), the Post doctoral Fellowship Program of CPSF (No. GZC20232390), the Qingchuang Science and Technology Plan of Shandong Province (No. 2021KJ054), the Foundation of Dezhou University (HXKT2022309) and the Talent Introduction Program of Dezhou University (30101421).

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Footnotes

† Electronic supplementary information (ESI) available: PXRD, TGA, structures, UV spectra, crystal data, and experimental details. CCDC 2442522–2442529. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5mh00689a

‡ These authors contributed equally to this work.

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