P. Van der Voort

Porous organic polymers as metal free heterogeneous organocatalysts

M. Debruyne, V. Van Speybroeck, P. Van der Voort, C. Stevens
Green Chemistry
Volume 23, Issue 19, Page 7361-7434
2021
A1

Abstract 

Efficient catalysis is essential from a green chemistry perspective. Porous organic polymers (POPs) have recently emerged as highly effective materials for catalytic applications. POPs possess controllable compositions and functionalities, high surface areas and can be very stable. In this review we focus on the application of POPs as metal free heterogeneous organocatalysts, a booming field in green chemistry. Acid, base, combined acid-base and hydrogen bonding catalysis are addressed. In addition, chiral catalysis and CO2 utilization with POPs are discussed. The aim is to provide a comprehensive overview of the field, exploring all different types of POPs as metal free catalysts. Special attention is given to the synthesis conditions to provide the reader with more insight into the construction of these types of materials.

DOI 

10.1039/d1gc02319e

Synthesis of Nitrile-Functionalized Polydentate N-Heterocycles as Building Blocks for Covalent Triazine Frameworks

J. Everaert, M. Debruyne, F. Vandenbussche, K. Van Hecke, T.S.A Heugebaert, P. Van der Voort, V. Van Speybroeck, C. Stevens
Synthesis-Stuttgart
2021
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Abstract 

Covalent triazine frameworks (CTFs) based on polydentate ligands are highly promising supports to anchor catalytic metal complexes. The modular nature of CTFs allows to tailor the composition, structure, and function to its specific application. Access to a broad range of chelating building blocks is therefore essential. In this respect, we extended the current available set of CTF building blocks with new nitrile-functionalized N-heterocyclic ligands. This paper presents the synthesis of the six ligands which vary in the extent of the aromatic system and the denticity. The new building blocks may help in a rational design of enhanced support materials in catalysis.

Hydrogen Clathrates: Next Generation Hydrogen Storage Materials

A. Gupta, G.V. Baron, P. Perreault, S. Lenaerts, R.-G. Ciocarlan, P. Cool, P. M. Mileo, S.M.J. Rogge, V. Van Speybroeck, G. Watson, P. Van der Voort, M. Houlleberghs, E. Breynaert, J.A. Martens, J.F.M. Denayer
Energy Storage Materials
41, 69-107
2021
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Abstract 

Extensive research has been carried on the molecular adsorption in high surface area materials such as carbonaceous materials and MOFs as well as atomic bonded hydrogen in metals and alloys. Clathrates stand among the ones to be recently suggested for hydrogen storage. Although, the simulations predict lower capacity than the expected by the DOE norms, the additional benefits of clathrates such as low production and operational cost, fully reversible reaction, environmentally benign nature, low risk of flammability make them one of the most promising materials to be explored in the next decade. The inherent ability to tailor the properties of clathrates using techniques such as addition of promoter molecules, use of porous supports and formation of novel reverse micelles morphology provide immense scope customisation and growth. As rapidly evolving materials, clathrates promise to get as close as possible in the search of “holy grail” of hydrogen storage. This review aims to provide the audience with the background of the current developments in the solid-state hydrogen storage materials, with a special focus on the hydrogen clathrates. The in-depth analysis of the hydrogen clathrates will be provided beginning from their discovery, various additives utilised to enhance their thermodynamic and kinetic properties, challenges in the characterisation of hydrogen in clathrates, theoretical developments to justify the experimental findings and the upscaling opportunities presented by this system. The review will present state of the art in the field and also provide a global picture for the path forward.

Gold Open Access

Overview of N-rich antennae investigated in lanthanide-based temperature sensing

F. Vanden Bussche, A.M. Kaczmarek, V. Van Speybroeck, P. Van der Voort, C.V. Stevens
Chemistry - A European Journal
27 (25), 7214-7230
2021
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Abstract 

The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide‐based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light‐harvesting antenna is required. This Review provides an overview of the nitrogen‐rich antennae in lanthanide‐based temperature sensors, emitting in the visible light spectrum, and discusses their temperature sensor ability. The N‐rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. Molecular probes, consisting of small molecules, are first discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di‐ and polynuclear complexes, metal–organic frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal–organic frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range, and porous organic polymers are operative in the cryogenic‐to‐medium temperature range.

Open Access version available at UGent repository

DOI 

10.1002/chem.202100007

Identification of vanadium dopant sites in the metal–organic framework DUT-5(Al)

K. Maes, L.I.D.J. Martin, S. Khelifi, A.E.J. Hoffman, K. Leus, P. Van der Voort, E. Goovaerts, P.F. Smet, V. Van Speybroeck, F. Callens, H. Vrielinck
Physical Chemistry Chemical Physics (PCCP)
23, 7088-7100
2021
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Abstract 

Studying the structural environment of the VIV ions doped in the metal–organic framework (MOF) DUT-5(Al) ((AlIIIOH)BPDC) with electron paramagnetic resonance (EPR) reveals four different vanadium-related spectral components. The spin-Hamiltonian parameters are derived by analysis of X-, Q- and W-band powder EPR spectra. Complementary Q-band Electron Nuclear DOuble Resonance (ENDOR) experiments, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), X-Ray Diffraction (XRD) and Fourier Transform InfraRed (FTIR) measurements are performed to investigate the origin of these spectral components. Two spectral components with well resolved 51V hyperfine structure are visible, one corresponding to VIV=O substitution in a large (or open) pore and one to a narrow (or closed) pore variant of this MOF. Furthermore, a broad structureless Lorentzian line assigned to interacting vanadyl centers in each other's close neighborhood grows with increasing V-concentration. The last spectral component is best visible at low V-concentrations. We tentatively attribute it to (VIV=O)2+ linked with DMF or dimethylamine in the pores of the MOF. Simulations using these four spectral components convincingly reproduce the experimental spectra and allow to estimate the contribution of each vanadyl species as a function of V-concentration.

Quantifying the likelihood of structural models through a dynamically enhanced powder X‐ray diffraction protocol

S. Borgmans, S.M.J. Rogge, J. De Vos, C.V. Stevens, P. Van der Voort, V. Van Speybroeck
Angewandte Chemie int. Ed.
60 (16), 8913-8922
2021
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Abstract 

Structurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure‐function relations and enable functional material design. Herein a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X‐ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.

Gold Open Access

Strongly Reducing (Diarylamino)benzene Based Covalent Organic Framework for Metal-Free Visible Light Photocatalytic H2O2 Generation

C. Krishnaraj, H. S. Jena, L. Bourda, A. Laemont, P. Pachfule, J. Roeser, C. V. Chandran, S. Borgmans, S.M.J. Rogge, K. Leus, C.V. Stevens, J.A. Martens, V. Van Speybroeck, E. Breynaert, A. Thomas, P. Van der Voort
JACS (Journal of the American Chemical Society)
142 (47), 20107-20116
2020
A1

Abstract 

Photocatalytic reduction of molecular oxygen is a promising route toward sustainable production of hydrogen peroxide (H2O2). This challenging process requires photoactive semiconductors enabling solar energy driven generation and separation of electrons and holes with high charge transfer kinetics. Covalent organic frameworks (COFs) are an emerging class of photoactive semiconductors, tunable at a molecular level for high charge carrier generation and transfer. Herein, we report two newly designed two-dimensional COFs based on a (diarylamino)benzene linker that forms a Kagome (kgm) lattice and shows strong visible light absorption. Their high crystallinity and large surface areas (up to 1165 m2·g−1) allow efficient charge transfer and diffusion. The diarylamine (donor) unit promotes strong reduction properties, enabling these COFs to efficiently reduce oxygen to form H2O2. Overall, the use of a metal-free, recyclable photocatalytic system allows efficient photocatalytic solar transformations.

Gold Open Access

Structural and photophysical properties of various polypyridyl ligands: A combined experimental and computational study

L. De Bruecker, J. Everaert, P. Van der Voort, C.V. Stevens, M. Waroquier, V. Van Speybroeck
ChemPhysChem
21 (22), 2489–2505
2020
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Abstract 

Covalent triazine frameworks (CTFs) with polypyridyl ligands are very promising supports to anchor photocatalytic complexes. Herein, we investigate the photophysical properties of a series of ligands which vary by the extent of the aromatic system, the nitrogen content and their topologies to aid in selecting interesting building blocks for CTFs. Interestingly, some linkers have a rotational degree of freedom, allowing both a trans and cis structure, where only the latter allows anchoring. Therefore, the influence of the dihedral angle on the UV‐Vis spectrum is studied . The photophysical properties are investigated by a combined computational and experimental study. Theoretically, both static and molecular dynamics simulations are performed to deduce ground‐ and excited state properties based on density functional theory (DFT) and time‐dependent DFT. The position of the main absorption peak shifts towards higher wavelengths for an increased size of the π‐system and a higher π‐electron deficiency. We found that the position of the main absorption peak among the different ligands studied in this work can amount to 271 nm; which has a significant impact on the photophysical properties of the ligands. This broad range of shifts allows modulation of the electronic structure by varying the ligands and may help in a rational design of efficient photocatalysts.

Gold Open Access

N‐rich porous polymer with isolated Tb3+‐ions displays unique temperature dependent behavior through the absence of thermal quenching

F. Vanden Bussche, A.M. Kaczmarek, S. K. P. Veerapandian, J. Everaert, M. Debruyne, S. Abednatanzi, R. Morent, N. De Geyter, V. Van Speybroeck, P. Van der Voort, C.V. Stevens
Chemistry - A European Journal
26 (67), 15596-15604
2020
A1

Abstract 

The challenge of measuring fast moving or small scale samples is based on the absence of contact betw een sample and sensor. Grafting lanthanides onto hybrid materials arises as one of the most promising accurate techniques to obtain noninvasive thermometers. In this w ork, a novel bipyridine based Porous Organic Polymer (bpyDATPOP) wasinvestigatedastemperaturesensorafter grafting w ith Eu(acac) 3 and Tb(acac) 3 complexes. The bpyDAT POP successfully showed temperature dependent behavior in the 10 ‐ 310 K range, proving the potential of amorphous, porous organic framew orks. More intriguingly, w e observed unique temperature dependent behavior; instead of the standard observed change in emission as a result of a change in temperature for both Eu 3+ and Tb 3+ , the emission spectrumof Tb 3+ remained constant. This w ork provides framework‐ and energy‐based explanations for the observed phenomenon. The conjugation in the bpyDAT POP framew ork is interrupted, creating energetically isolated Tb 3+ environments. Energy transferfromTb 3+ toEu 3+ isthereforeabsent,norenergybacktransfer from Tb 3+ to bpyDAT POP ligand (i.e. no thermal quenching) is detected.

Open Access version available at UGent repository
Gold Open Access

Elucidating the promotional effect of a covalent triazine framework in aerobic oxidation

S. Abednatanzi, P. Gohari Derakhshandeh, P. Tack, F. Muniz-Miranda, Y-Y Liu, J. Everaert, M. Meledina, F. Vanden Bussche, L. Vincze, C. Stevens, V. Van Speybroeck, H. Vrielinck, F. Callens, K. Leus, P. Van der Voort
Applied Catalysis B: Environmental
269, 118769
2020
A1

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