Preparation and Applications of Metal-Organic Frameworks (MOFs): A Laboratory Activity and Demonstration for High School and/or Undergraduate Students.

The chemistry of metal-organic frameworks (MOFs), a new class of emerging crystalline porous solids with three-dimensional (3D) networks composed of metals and multidentate organic molecules, was introduced by using three differently-shaped crystals. We reported new and mild MOF synthesis methods that are simple and devised to be performed in high school or primarily undergraduate school settings. MOF applications were demonstrated by use of our synthesized MOFs in the capture of iodine as a potentially hazardous molecule from solution and as a drug delivery system. These applications can be visually confirmed in minutes. Students can gain knowledge on advanced topics, such as drug delivery systems, through these easy-to-prepare MOFs. Furthermore, students can gain an understanding of powder X-ray analysis and ultraviolet-visible near-infrared spectroscopy. This laboratory experience is practical, including synthesis and application of MOFs. The entire experiment has also been recorded as an educational video posted on YouTube as a free public medium for students to watch and learn. In this article we first report the steps we took to synthesize and analyze the MOFs, followed by a description of a simple demonstration that we verified to effectively exhibit adsorption by MOFs. We conclude with a description of how the laboratory activity and demonstration was implemented in an undergraduate chemistry laboratory.

Using a Faculty-Developed Documentary-Style Film to Communicate Authentic Chemistry Research to a High School Audience.

Described is the creation, deployment, and evaluation of a video produced about the synthesis and applications of metal-organic frameworks (MOFs). The goal of this project was to gauge the impact of viewing the video on high school students' conceptions of authentic chemistry practices and applications. Additionally, comparisons were made between the use of the video and more traditional face-to-face presentations given by professional scientists. Observations, student surveys, and an interview with the high school chemistry teacher demonstrated the utility of such a video. Specifically, the students who viewed the video reported learning more about the nature of laboratory work in chemistry than other students who did not view the video. Students, regardless of whether they viewed the video or just received a presentation, reported growth in understandings of the applications of chemistry research and porous nanomaterial. Other research chemists are encouraged to consider ways that they could document on video the research that they are performing in order to introduce an untapped audience (high school students) to authentic chemistry research in a practically simple manner. During times of crisis, such as a pandemic, online videos could be a useful tool for high school chemistry teachers to use in collaboration with research faculty, particularly when schools are closed.

Red-Colored Circularly Polarized Luminescence from a Benzo-Fused BODIPY-BINOL Complex.

Red emission with sharp bandwidth and high quantum yield is a desired characteristic for organic chromophores in optoelectronic, spintronic, and biomedical applications. Here, we observe circularly polarized luminescence (CPL) with these characteristics from a benzo-fused BODIPY-BINOL complex (1). Using time-resolved optical spectroscopy, electrochemistry, and density functional theory calculations, we showed that the emissive excited state of 1 does not have a charge-transfer (CT) character, unlike that of the regular BODIPY counterpart (2). The rigidity and the lack of CT character make this class of molecules an appealing platform for CPL-active molecules in the red spectral region, with ample room for improvement in the dissymmetry factor and brightness.

Acceleration of Nonradiative Charge Recombination Reactions at Larger Distances in Kinked Donor-Bridge-Acceptor Molecules.

Photoinduced electron transfer in donor-bridge-acceptor (D-B-A) molecular systems can occur via tunneling over long distances (rDA) of well over 10 Å. We commonly observe decreasing rates of electron transfer with increasing distances, a result of a decrease in the electronic coupling of the donor and acceptor moiety. In the study of D-B-A molecules with Ru(bpy)32+ as a bridge/core, Kuss-Petermann and Wenger observed the opposite trend (J. Am. Chem. Soc.2016, 138, 1349); a maximum rate constant of electron transfer was observed at an intermediate electron transfer distance. Within the high-temperature limit of the classical Marcus equation, their observation was qualitatively explained by a sharp distance dependence of outer sphere (or solvent) reorganization energy, as predicted by Sutin and co-workers (J. Am. Chem. Soc.1984, 106, 6858), and almost distance-independent electronic couplings. Here, we report another example of such an underexplored behavior with three kinked D-B-A systems of rDA ∼ 10-19 Å, showing increasing rates of nonradiative charge recombination with increasing rDA. The three D-B-A systems are based on boron dipyrromethene and triphenylamine as electron acceptor and donor groups, respectively, with aryl bridges where the donor and acceptor moieties are connected at meso-positions. These D-B-A molecules exhibit radiative electron transfer reactions (or charge-transfer emission), which enables us to experimentally determine the solvent reorganization energy and the electronic couplings. The analysis of charge-transfer emission that explicitly considers electron-vibration coupling, in conjunction with the temperature-dependent analysis and computational method, revealed that the solvent reorganization energy indeed increases with distance, and at the same time, the electronic coupling decreases with distance expectedly. Therefore, under the right conditions for solvent reorganization energy and electronic coupling values, our results show that we can observe the acceleration of electron transfer reactions with increasing distance, even when we have the expected distance dependence of electronic coupling. This work indicates that the acceleration of electron transfer with increasing distance may be achieved with a fine-tuning of molecular design.

meso-Antracenyl-BODIPY Dyad as a New Photocatalyst in Atom-Transfer Radical Addition Reactions.

We demonstrate that because of the efficient generation of triplet excited state under UV or visible-light irradiation, meso-antracenyl-BODIPY donor-acceptor dyad can catalyze atom-transfer radical addition (ATRA) reactions between bromomalonate and alkenes. This finding paves the way for the design and application of the new type of heavy atom-free organic chromophores for photocatalysis.

A Bio-Conjugated Chlorin-Based Metal-Organic Framework for Targeted Photodynamic Therapy of Triple Negative Breast and Pancreatic Cancers.

The field of photodynamic therapy (PDT) has continued to show promise as a potential method for treating tumors. In this work a photosensitizer (PS) has been delivered to cancer cell lines for PDT by incorporation into the metal-organic framework (MOF) as an organic linker. By functionalizing the surface of MOF nanoparticles with maltotriose the PS can efficiently target cancer cells with preferential uptake into pancreatic and breast cancer cell lines. Effective targeting overcomes some current problems with PDT including long-term photosensitivity and tumor specificity. Developing a PS with optimal absorption and stability is one of the foremost challenges in PDT and the synthesis of a chlorin which is activated by long-wavelength light and is resistant to photo-bleaching is described. This chlorin-based MOF shows anti-cancer ability several times higher than that of porphyrin-based MOFs with little toxicity to normal cell lines and no dark toxicity.

Pt(II)-Decorated Covalent Organic Framework for Photocatalytic Difluoroalkylation and Oxidative Cyclization Reactions.

A new covalent organic framework (COF) based on imine bonds was assembled from 2-(4-formylphenyl)-5-formylpyridine and 1,3,6,8-tetrakis(4-aminophenyl)pyrene, which showed an interesting dual-pore structure with high crystallinity. Postmetallation of the COF with Pt occurred selectively at the N donor (imine and pyridyl) in the larger pores. The metallated COF served as an excellent recyclable heterogeneous photocatalyst for decarboxylative difluoroalkylation and oxidative cyclization reactions.

Maltotriose Conjugated Metal-Organic Frameworks for Selective Targeting and Photodynamic Therapy of Triple Negative Breast Cancer Cells and Tumor Associated Macrophages.

Herein, we report a nano-MOF conjugated to maltotriose as a new DDS. MA-PCN-224-0.1Mn/0.9Zn showed its ability to target cancer and TAM. This novel MOF is an effective PDT agent and shows little dark toxicity, MA-PCN-224-0.1Mn/0.9Zn uptakes selectively into cancer cells. A well-suited size control methodology was used so that the nano-scaled MOFs may take advantage of the EPR effect. This development of a nano-scale MOF for PDT that is conjugated to a cancer targeting ligand represents a meaningful development for the use of MOFs as drug delivery systems.

(Thio)urea-Based Covalent Organic Framework as a Hydrogen-Bond-Donating Catalyst.

Two-dimensional urea- and thiourea-containing covalent organic frameworks (COFs) were synthesized at ambient conditions at large scale within 1 h in the absence of an acid catalyst. The site-isolated urea and thiourea in the COF showed enhanced catalytic efficiency as a hydrogen-bond-donating organocatalyst compared to the molecular counterparts in epoxide ring-opening reaction, aldehyde acetalization, and Friedel-Crafts reaction. The COF catalysts also had excellent recyclability.