Using the Luminescence and Ion Sensing Experiment of a Lanthanide

Apr 17, 2019 - An integrated and research-focused laboratory experiment is developed to introduce the “antenna effect” occurring in luminescent la...
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Using the Luminescence and Ion Sensing Experiment of a Lanthanide Metal−Organic Framework to Deepen and Extend Undergraduates’ Understanding of the Antenna Effect Min Yuan,† Qun Tang,‡ Ying Lu,*,† Zhong Zhang,† Xiao-Hui Li,† Shu-Mei Liu,† Xiu-Wei Sun,† and Shu-Xia Liu*,†

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Key Laboratory of Polyoxometalate Science of the Ministry of Education, College of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China ‡ Guangxi Key Laboratory of Electrochemical and Magneto-chemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin, Guangxi 541004, P. R. China S Supporting Information *

ABSTRACT: An integrated and research-focused laboratory experiment is developed to introduce the “antenna effect” occurring in luminescent lanthanide complexes to students. Students synthesized a lanthanide metal−organic framework (Ln-MOF) with the formula of [Eu(BTPCA)(H2O)]·2DMF·nH2O (Eu-BTPCA, H3BTPCA = 1,1′,1″(1,3,5-triazine-2,4,6-triyl)tripiperidine-4-carboxylic acid) by the solvothermal method and characterized its structure by powder X-ray diffraction. They then measured the luminescence spectrum of EuBTPCA and compared it with that of EuCl3. Finally, students performed the luminescent sensing studies to metal ions. This experiment lets students gain the first-hand experience of solvothermal syntheses of MOFs and introduces essential scientific research approaches to students as well as exposes students to modern instrumental techniques for chemical research. Most importantly, through this experiment and its outcomes analyses, students can better understand the “antenna effect” and witness its application in metal ion luminescent sensing. KEYWORDS: Upper-Division Undergraduate, Inorganic Chemistry, Laboratory Instruction, Hands-On Learning/Manipulatives, Coordination Compounds, Fluorescence Spectroscopy

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endeavors from the scientific community on lanthanide complexes. The dearth of teaching experiments on lanthanide complexes makes it difficult for students to comprehend the basic concepts and theories of lanthanide chemistry as well the instructive photophysical properties of f-block elements. Although the antenna effect has been widely confirmed by numerous research on luminescence properties of lanthanide complexes, it is not found in the student laboratories. As a complementary knowledge of lanthanide chemistry, it is necessary for students to learn the light conversion process of the antenna effect. Especially important, the intramolecular energy transfer involved in the antenna effect can help students to comprehend the luminescence mechanism in essence. The literature in the Journal of Chemical Education provide a solid platform for students to gain insight into lanthanide chemistry. Some articles in the journal introduce teaching experiments about lanthanide complexes, for example, the kinetic study of

he luminescence properties of lanthanide complexes have been fascinating researchers for decades.1,2 Lanthanide ions (Ln3+) are characterized by a gradual filling of the 4f orbitals, from 4f0 (for La3+) to 4f14 (for Lu3+). These electronic [Xe]4fn configurations (n = 0−14) create diverse electronic energy levels, leading to the interesting luminescent properties. All lanthanide ions except La3+ and Lu3+ can create luminescent f−f emissions from ultraviolet (UV) to visible and near-infrared (NIR) regions. However, the direct absorption of light by the lanthanide ions in the UV region is very weak owing to their parity-forbidden f−f transitions, resulting in weak luminescence intensity. To circumvent this problem, organic ligands possessing strong absorption in the UV region were used to sensitize the luminescence of Ln3+ by transferring energy to the Ln3+ ions inducing Ln-centered emission, which is widely referred to as the “antenna effect”.3−5 Introductions of lanthanide chemistry are commonly set at the end of most inorganic courses and usually only shortly included in a one-semester advanced course. Moreover, the undergraduate experiments involving lanthanide complexes are very limited despite extensive and increasing research © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: January 25, 2019 Revised: March 29, 2019

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DOI: 10.1021/acs.jchemed.9b00075 J. Chem. Educ. XXXX, XXX, XXX−XXX

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simple lanthanide-organic hybrid as a medium to demonstrate the antenna effect, which not only introduces the advances in a current research hotspot field to laboratory courses but also connects the laboratory experiment to students’ everyday lives due to the sensing function of Ln-MOFs relevant to the environment and human health.

the radiative relaxation process of lanthanides-activated phosphors6 and the quenched mechanistic study of terbium complex phosphorescence.7 However, the antenna effect was mentioned in the journal only as a part of the Introduction of the articles about lanthanide chemistry experiments, and there is no specific article that introduces the antenna effect to students.8,9 Herein, a research-focused laboratory experiment is described, which includes the synthesis, characterization, luminescence, and ion sensing testing of a lanthanide metal− organic framework (Ln-MOF). In this laboratory experiment, first, students were required to prepare a Ln-MOF [Eu(BTPCA)(H2O)]·2DMF·nH2O (Eu-BTPCA, H3BTPCA = 1,1′,1″-(1,3,5-triazine-2,4,6-triyl)tripiperidine-4-carboxylic acid) by the solvothermal method and characterize its structure by powder X-ray diffraction (PXRD). Starting from synthesizing their own batches of Ln-MOF, the students can appreciate the process of preparing a useful complex that they will utilize later. Then, students determined the luminescent spectra of Eu-BTPCA and EuCl3. Through comparing the luminescence spectra of Eu-BTPCA and EuCl3, the antenna effect can be revealed, that is the lanthanides themselves exhibit weak luminescence which can be enhanced by complexation with an appropriate ligand. The experimental results help students to build a deeper comprehension of the antenna effect. Finally, for the sensing studies of Eu-BTPCA to metal ions, this part not only presents students an example of the application of luminescent Ln-MOF materials but also offers students a further understanding for the antenna effect through observing the luminescent enhancement or quenching by the increase and reduction of the antenna effect. This experiment was designed for use as an upper-level undergraduate advanced or integrated-style chemistry laboratory. The experimental approach is based upon our recent study about cation sensing by a luminescent MOF with multiple Lewis basic sites.10,11 This research-focused laboratory experiment was designed to enable students to apply the foundational chemistry knowledge they have learned in the classroom, such as the elements of coordination chemistry, mechanism of intramolecular energy transfer, the intrinsic characteristics of lanthanide ions, microstates and term symbols to analyze and discuss the experimental outcomes. The advantages of integrating discovery-based research into the laboratory experiment include promoting student learning and diversity, introducing essential research approaches to students, and exposing students to modern instrumental techniques for chemical research. MOFs have been emerging as very important hybrid materials in the last 2 decades due to their structural diversity and extensive applications.12,13 As a class of crystalline microporous materials, MOFs have the unique and advantageous feature of high structural tunability via changes in the compositions of the metal clusters and/or organic linkers. LnMOFs often exhibit remarkable luminescent properties owing to the intrinsic luminescent features of lanthanide ions and the antenna effect (energy transfers between ligands and lanthanide centers). Moreover, the inherent porosity with unique luminescent property has enabled Ln-MOFs to be a very promising type of sensing materials with high sensitivity and selectivity. The Ln-MOFs sensor to metal ions can be utilized to efficiently probe hazardous metal ions in the environment and trace elements in biological systems. This current laboratory experiment utilized a Ln-MOF instead of a

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EXPERIMENTAL DETAILS This experiment can be divided into three stages: (1) the synthesis and characterization of Eu-BTPCA; (2) luminescence measurements of H3BTPCA, Eu-BTPCA, and EuCl3; and (3) metal ions sensing studies. First, students can complete the synthesis of Eu-BTPCA by maintaining the mixture of EuCl3·nH2O and H3BTPCA (1:1 molar ratio) in DMF/H2O (1:1 volume ratio) in a 65 °C oil bath for 3 days. All of the above starting materials except organic ligand H 3 BTPCA are commercially available. H3BTPCA can be purchased from some chemical reagent companies with made-to order service. Alternatively, H3BTPCA can also be synthesized easily with a considerable yield (83%) in the laboratory according to the procedure described in the literature.14 Students can characterize the structure of the synthesized Eu-BTPCA by PXRD. Second, photoluminescence spectra of H3BTPCA, EuBTPCA and EuCl3 were measured. Third, Eu-BTPCA was thermally treated in the vacuum, 130 °C, remaining 24 h to remove aqua ligand and the solvent molecules of crystallization, and affording activated sample EuBTPCA*. Eu-BTPCA* was characterized by PXRD and infrared (IR). After activation, Eu-BTPCA* (20 mg) was immersed in pure dimethylformamide (DMF) solvent and 10 mL 0.01 mol/L DMF solution containing various metal ions Mn+ (Mn+ = Mn2+, Fe3+, Ni2+, Cu2+, Co2+, Cr3+, and Zn2+) for 24 h, then filtered, rinsed, and dried to obtain (Eu-BTPCA)· nDMF and Mn+⊂ (Eu-BTPCA), respectively. Students characterized Mn+⊂ (Eu-BTPCA) and (Eu-BTPCA)·nDMF by PXRD. And students measured the photoluminescence spectra of the obtained Mn+⊂ (Eu-BTPCA) and (Eu-BTPCA)· nDMF. All of the above-mentioned PXRD measurements should be performed in the angular range 2θ 5−45° with a step size of 0.02. FTIR should be recorded in the range 400−4000 cm−1 using KBr pellets. Photoluminescence spectra of Eu-BTPCA and Mn+⊂ (Eu-BTPCA) should be measured with an excitation wavelength at 395 and 344 nm, respectively. Their characteristic emissions are recorded at 618 nm. Students should complete the characterizations of samples under the guidance of the instructor because the modern analysis techniques, such as PXRD, IR, and fluorescence spectroscopy, are not widely used in the undergraduate laboratory.

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HAZARDS DMF, although it is a common organic solvent, its danger also should be noted due to irritation to the eyes, nose, and throat. H3BTPCA can cause damage to the skin. The causticity and toxic of transition metal ions should not be ignored. So, students should wear appropriate protective clothing, gloves, and goggles or masks all the time. It is necessary for students to find out the hazards of reagents in advance and record them in the experimental record. Instructor should be responsible for checking the safety protection before the experiment. Furthermore, students should pay attention to the use of the B

DOI: 10.1021/acs.jchemed.9b00075 J. Chem. Educ. XXXX, XXX, XXX−XXX

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six Eu3+ ions utilizing exclusively its carboxylate groups, two of which are in a bridging-chelating coordination mode and the third is in a bridging fashion. Each Eu3+ ion is nine-coordinated in a monocapped square antiprism geometry with one aqua ligand and eight oxygen atoms from six different BTPCA ligands. Such connections between Eu3+ ions and BTPCA ligands lead to an open framework with 1D channel along the crystallographic c axis. The instructor can properly guide students to use coordination chemistry knowledge they have learned in the classroom to understand the structure of EuBTPCA.

oil bath as heating container. Students should wear antiultraviolet goggles in case eyes are exposed to intense ultraviolet when they use ultraviolet light to irradiate samples.

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RESULTS AND DISCUSSION It is recommended that participating students have completed the basic courses of inorganic chemistry, physical chemistry, and spectrum analysis. The scale of the experiment is regulated by about 28 students, which can be divided into four groups. It takes a week to complete the entire experiment, including the wait time of solvothermal synthesis, activation, the metal sensing experiment, and characterization. In the case that H3BTPCA needs to be synthesized by the students, 1 more week is needed. Students can take advantage of the waiting time to learn the scientific software, such as Mercury and Origin. The experiment is particularly suitable for the chemistry laboratory due to the nontoxic and relatively inexpensive starting materials, mild reaction conditions, simple experimental procedures, and availability of instruments. It can be repeated many times in a semester according to the number of students who volunteer to participate.

Luminescence of H3BTPCA, Eu-BTPCA and EuCl3

The luminescence spectra of H3BTPCA, Eu-BTPCA, and EuCl3 were recorded. At the excitation wavelength of 348 nm, H3BTPCA exhibits an intense emission band at 438 nm, which is attributed to the π−π* electronic transition (Figure 2).

Synthesis and Characterization of Eu-BTPCA

Eu-BTPCA was synthesized under mild conditions by the solvothermal method. The solvothermal method is the main synthetic method of MOFs, which is extensively used in the MOFs syntheses.15,16 The solvothermal synthesis of EuBTPCA is carried out in relatively low temperature (65 °C), thus this synthestic experiment is safer than most MOFs syntheses. Using the described synthetic procedure (Figure 1), Figure 2. Excitation (red) and emission (black) spectra of powder sample H3BTPCA.

Upon excitation at 395 nm, both the luminescence spectra of Eu-BTPCA and EuCl3 show the characteristic transitions of the Eu3+ ion. The peaks at 590, 614, 650, and 702 nm are assigned to the 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7 F4 transitions, respectively. Among the 5D0 → 7Fn (n = 1−4) transitions, 5D0 → 7F1 (magnetic coupling transition) and 5D0 → 7F2 (electrical coupling transition) are the two strongest emissions, which are used for structural determination and sensing studies. Notably, the luminescence spectrum of EuBTPCA exhibits remarkable luminescence enhancement compared to that of EuCl3. The intensity of the red luminescence of Eu-BTPCA monitored at 614 nm for the 5 D0 → 7F2 transition reaches 3 times that of EuCl3, demonstrating the antenna effect of the BTPCA ligand to the luminescence of Eu3+ ion (Figure 3). Moreover, the emission of ligand at 445 nm is not observed in the luminescence spectrum of Eu-BTPCA, which further indicates that BTPCA is an excellent antenna ligand to achieve efficient energy transfer to the Eu3+. Except through comparing the luminescence spectra of Eu-BTPCA and EuCl3, students can also experience the luminescence enhancement induced by the antenna effect through direct observation by eye. Students can observe that Eu-BTPCA displays more intense red emission compared with EuCl3 when they are exposed to ultraviolet light. Combining the above experimental results, students should discuss the energy transfer mechanism involved in the antenna effect in their experimental reports utilizing the knowledge they have learned in the classroom. The commonly accepted

Figure 1. Solvothermal reaction to form Eu-BTPCA and packing of Eu-BTPCA as viewed slightly off the c axis (The coordinated water molecules, free solvate molecules, and H atoms were omitted for clarity). Colors: C (gray), N (blue), O (red), Eu (green).

Eu-BTPCA can be synthesized in pure phase with a relatively high yield. Through this synthetic experiment, students cannot only practice their synthetic skills but also get knowledge of the general procedure of solvothermal MOF syntheses. The obtained Eu-BTPCA sample was characterized by PXRD. The PXRD pattern of the as-prepared Eu-BTPCA sample is well consistent with the stimulated one from the reported crystal data of Eu-BTPCA, which suggests that the asprepared Eu-BTPCA sample possesses the same structure as the reported Ln-MOF Eu-BTPCA (Figure S5). The students can learn about the structure of Eu-BTPCA by reading the original literature about Eu-BTPCA.10 For the students interested in crystal structure, they also can utilize the crystal data of Eu-BTPCA to view its structure by the free Mercury software offered by the Cambridge Crystallographic Data Centre. The framework of Eu-BTPCA is built by Eu3+ ions connected by BTPCA ligands. Each BTPCA linker coordinates C

DOI: 10.1021/acs.jchemed.9b00075 J. Chem. Educ. XXXX, XXX, XXX−XXX

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or undergo nonradiative intersystem crossing (ISC) to the excited triplet state T1. The T1 state can radiate to the ground state S0 to generate ligand phosphorescence. Alternatively, the T1 state can transfer energy to excited 4f states of the lanthanide ions. After this indirect excitation by energy transfer (ET), the lanthanide ions in the excited state can radiate to the 4f ground state, emitting characteristic f−f linear spectra. A main energy transfer path can be remembered: S0 → S1, S1 → T1, T1 → Ln3+, lanthanide-centers emission. After the discussion of the mechanism of Ln-MOF luminescence, students were encouraged to discuss how to select the antenna organic ligands. The discussion may be carried out in a research team and extensively combined with the research work in the literature. It can be concluded that the deliberate choice of organic ligands is of great significance to ensure the effective achievement of the antenna effect: First, the organic ligands are required to possess strong coordination ability to Ln3+ ion; second, the organic ligands are demanded to have strong ultraviolet light harvesting ability. Organic ligands with highly-conjugated π electrons are excellent candidates; third, for the efficient energy transfer from ligands to Ln3+ ions, the triplet state of the ligand must be a good energy match with the excited state of Ln3+ ion.

Figure 3. Emission spectrum of powder samples Eu-BTPCA and EuCl3 (excitation at 395 nm). Inset: the image of the Eu-BTPCA and EuCl3 under excitation by UV light irradiation.

mechanism could be illustrated by a Jablonski’s diagram,17 as shown in Figure 4: the organic ligands of the lanthanide

Metal Ion Sensing Studies

In this experiment, the selection of H3BTPCA as a ligand for the synthesis of luminescent Ln-MOF is not only due to the strong coordination ability of its carboxylate groups to the Ln3+ ion and the strong UV harvesting ability of its triazinyl group benefiting for the antenna effect but also its accessible Lewis basic N atoms allowing for ion sensing studies. Owing to the preferential binding of Ln3+ ions to carboxylate oxygen atoms over triazinyl nitrogen atoms, H3BTPCA exclusively utilizes its carboxylate groups to coordinate with Ln3+ ions. The Lewis basic triazinyl N atoms of H3BTPCA ligand project into the channels of the framework and are accessible for interactions with incoming metal-ion guests. In order to fully expose the Lewis basic active sites inside the channels, Eu-BTPCA was first activated to remove the solvent molecules by thermal treatment. Using the activation procedure described in the Experimental Details, the aqua ligand and the solvent molecules filled in the channels of Eu-

Figure 4. Simplified Jablonski diagram for ligand-to-lanthanide energy transfer process. A = absorption, F = fluorescence, P = phosphorescence, L = lanthanide luminescence, ISC = intersystem crossing, ET = energy transfer, S = singlet, T = triplet.

complexes are excited by ultraviolet light to the excited singlet state Sn (S2 or S1). The molecules undergo vibrational relaxation (VR) and internal conversion (IC) to the lower vibrational level of the S1 excited state. Then, the S1 state can radiate to the ground state S0 to generate ligand fluorescence

Figure 5. (a) Emission spectrum of powder samples Mn+⊂ (Eu-BTPCA) and (Eu-BTPCA)·nDMF by immersing Eu-BTPCA* in 0.01 mol/L different metal ions and pure DMF solvent. (b) Bar diagram for the comparison luminescence intensity of Mn+⊂ (Eu-BTPCA) versus (EuBTPCA)·nDMF at 618 nm (excitation at 344 nm). The inset shows the contrastive photographs of (Eu-BTPCA)·nDMF and Mn+⊂ (Eu-BTPCA) under UV light irradiation. D

DOI: 10.1021/acs.jchemed.9b00075 J. Chem. Educ. XXXX, XXX, XXX−XXX

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BTPCA can be effectively removed. Comparing with the IR spectrum of Eu-BTPCA, the characteristic peak at 1675 cm−1 (CO stretching vibration of DMF molecule) and the broad peak at 3425 cm−1 (O−H stretching vibration of H2O molecule) are absent in the IR spectrum of the activated sample Eu-BTPCA*, which indicates the removal of DMF and H2O (Figure S6). The PXRD pattern of Eu-BTPCA* is in accordance with that of Eu-BTPCA, suggesting that the structure of framework remains intact after activation. The activated samples Eu-BTPCA* were immersed in DMF solution containing various metal ions to obtain Mn+⊂ (EuBTPCA) samples. The PXRD patterns of Mn+⊂ (Eu-BTPCA) samples are consistent with that of Eu-BTPCA, indicating that the structure of framework remains intact. The luminescence spectra of the Mn+⊂ (Eu-BTPCA) samples were shown in Figure 5, which display that various metal ions have obviously different effects on the luminescent intensity of Eu-BTPCA. Zn2+ markedly enhanced the luminescent intensity, whereas other metal ions (Mn2+, Fe3+, Ni2+, Cu2+, Co2+, Cr3+) caused varying degrees of quenching of the luminescence. Fe3+ had the most significant quenching effect, which almost completely quenched the luminescence of Eu3+. The above results indicate that Eu-BTPCA have the function of luminescent sensing of metal ions. Under UV light, students can clearly observe the quenching of Fe3+ and the enhancement of Zn2+ to the red luminescence of Eu-BTPCA by the naked eye. The extensively accepted explanation for the influences of incoming metal ions on the luminescence of Ln-MOF is that the electronic structure of the organic ligand is perturbed when it interacts with the incoming guest metal ions, which induce the changes of both its singlet and triplet excited states. These changes may facilitate or disrupt the energy transfer from organic ligand to Ln3+ ions, thus affecting the antenna efficiency of the organic ligand. The students are encouraged to find the explanation based on the energy transfer mechanism involved in antenna effect through consulting the literature.18,19 This approach may help students to further understand the antenna effect. Moreover, the students may carry out the discussion about the applications of the luminescent sensor of metal ions in a research team. Through the discussion, students may connect the laboratory experiment to their everyday lives, which will effectively inspire their study interests.

(4) What is the energy relationship between the T1 state of the ligand and the emission state of the lanthanide ions in Jablonski’s diagram? (5) What kind of organic ligand can be selected as an antenna ligand to sensitize lanthanide luminescence? Students can record the answers of the above questions in final reports. A qualified final report is required to include experimental goals, procedures, data processing, results and discussions, and citing references. The final report is an important indicator to assess the completion of the experiment. At the end of the report, students can make a real evaluation of the experiment so that instructors can make corresponding improvements to the experiment. Students are assessed on their practical performances and final lab reports. First, students can properly perform the synthetic experiment of Eu-BTPCA according to the given synthetic procedure and obtain Eu-BTPCA in pure-phase and sufficiently high yield, which suggests that students grasp the general solvothermal MOF synthetic method. Second, students are able to complete the PXRD, IR, and fluorescence spectroscopy measurements under the guidance of the instructor and analyze the obtained data to give correct conclusions, which indicate that students get knowledge of the modern instrumental techniques including PXRD, IR, and fluorescence spectroscopy. Third, students can correctly explain the luminescent enhancement of Eu-BTPCA in comparison to EuCl3 and the influence of incoming metal ions on the luminescence of Eu-BTPCA utilizing the antenna effect, which implies that students have a better understand about the antenna effect. Finally, students can give precise prelab answers, especially the detailed explanation of S1 state, T1 state, VR, IC, ISC in Jablonski’s diagram and discuss the intramolecular energy transfer process involved in the antenna effect combined with Jablonski’s diagram, which demonstrate that students have a deeper understanding of the antenna effect. Overall, students show a uniform success in the synthetic experiment and characterization measurements of Eu-BTPCA and a satisfactory ability to explain the changes of Eu3+-centers luminescence intensity using the antenna effect. The problem that students are not proficient in the S1 state, T1 state, VR, IC, ISC, and intramolecular energy transfer process involved in the antenna effect has also been overcome through group discussion. It was apparent from the students’ final reports that students in general had a profound understanding of the antenna effect.

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ASSESSMENT A detailed introduction about the electronic transitions of organic ligands, intramolecular energy transfer process, and the luminescence properties of lanthanide ions can be found in the Supporting Information. It is a challenge to understand Jablonski’s diagram after the experiment, which is mainly due to the fact that students are not familiar with some terms involved in Jablonski’s diagram, such as intersystem crossing (ISC), vibrational relaxation (VR), and internal conversion (IC). Therefore, it is particularly important for students to consult the laboratory handout according to the questions set by instructors in advance. The following prelab questions are used to ensure pedagogical goals were achieved: (1) What is antenna effect? (2) What is the entire light conversion process of the antenna effect? (3) Understand the scientific meaning of S1 state, T1 state, VR, IC, and ISC in Jablonski ’s diagram.

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SUMMARY We designed an integrated and research-focused laboratory experiment on the Ln-MOF (Eu-BTPCA) to deepen and extend the students’ comprehension of the antenna effect. In this experiment, students learn the general synthetic procedure of the solvothermal method extensively used in the MOFs syntheses. Students also have the hands-on experience in the modern instrumental techniques including PXRD, IR, and fluorescence spectroscopy and know what information these determinations can provide. Furthermore, very importantly, students can build a deeper comprehension of the antenna effect through the luminescence and sensing experiments as well as their outcomes analyses. Overall, this experiment could be an attractive addition to an undergraduate laboratory course which promotes student learning and diversity and stimulates E

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(11) Tang, Q.; Liu, S.; Liu, Y.; He, D.; Miao, J.; Wang, X.; Ji, Y.; Zheng, Z. Color tuning and white light emission via in situ doping of luminescent lanthanide metal-organic frameworks. Inorg. Chem. 2014, 53 (1), 289−293. (12) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Introduction to metalorganic frameworks. Chem. Rev. 2012, 112 (2), 673−674. (13) Cui, Y.; Li, B.; He, H.; Zhou, W.; Chen, B.; Qian, G. MetalOrganic Frameworks as Platforms for Functional Materials. Acc. Chem. Res. 2016, 49 (3), 483−493. (14) Zhao, X.; He, H.; Hu, T.; Dai, F.; Sun, D. Interpenetrating polyhedral MOF with a primitive cubic network based on supermolecular building blocks constructed of a semirigid C3-symmetric carboxylate ligand. Inorg. Chem. 2009, 48 (17), 8057−8059. (15) Farha, O. K.; Hupp, J. T. Rational design, synthesis, purification, and activation of metal-organic framework materials. Acc. Chem. Res. 2010, 43 (8), 1166−1175. (16) Stock, N.; Biswas, S. Synthesis of Metal-Organic Frameworks (MOFs): Routes to Various MOF Topologies, Morphologies, and Composites. Chem. Rev. 2012, 112 (2), 933−969. (17) Eliseeva, S. V.; Bunzli, J. C. Lanthanide luminescence for functional materials and bio-sciences. Chem. Soc. Rev. 2010, 39 (1), 189−227. (18) Hanaoka, K.; Kikuchi, K.; Kojima, H.; Urano, Y.; Nagano, T. Development of a zinc ion-selective luminescent lanthanide chemosensor for biological applications. J. Am. Chem. Soc. 2004, 126 (39), 12470−12476. (19) Chen, B.; Wang, L.; Xiao, Y.; Fronczek, F. R.; Xue, M.; Cui, Y.; Qian, G. A luminescent metal-organic framework with Lewis basic pyridyl sites for the sensing of metal ions. Angew. Chem., Int. Ed. 2009, 48 (3), 500−503.

students’ interests due to the sensing research closely relevant to students’ daily lives.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.9b00075. Students notices containing detailed background information, experimental instruction; and report requirements; instructor notes with chemical reagents and equipment, experiment procedure, data supplement, student feedback, and teaching summary (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Shu-Xia Liu: 0000-0003-0235-8594 Notes

The authors declare no competing financial interest. Crystallographic structural information can be provided.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 21231002, 21371029, 21671033, 91622108, and 21872021) and the Open Research Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (Jilin University, Grant No. 2015-01). The authors thank the undergraduate students for improving this experiment.

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REFERENCES

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