Real-world connections to sustainability: Using authentic learning activities to introduce students to systems thinking through green chemistry

Systems thinking refers to approaches to learning that emphasise the interdependence of components in dynamic systems and how they interact and influence one another (Mahaffy et al., 2019). Applying systems thinking to green chemistry teaching and learning can create a molecular basis for sustainability (Mahaffy et al., 2019) that is able to enhance undergraduate chemistry students’ multidimensional understanding of complex sustainability challenges (Smith, 2011). However, efforts to introduce sustainable systems thinking – specifically within first-year introductory chemistry courses – are particularly challenging, and past approaches have produced mixed success (Mahaffy et al., 2019; An et al., 2021). Consequently, this indicates an opportune space within undergraduate chemistry education research to explore alternative and multidisciplinary approaches towards teaching green chemistry and sustainability (Wissinger et al., 2021). In this research, we present the preliminary results of a trimester-long intervention using authentic learning activities to introduce first-year chemistry students to systems thinking, through the application of green chemistry concepts. To determine the effectiveness of the intervention, we are using a mixed-methods research design to assess the impact of the learning activities on students’ development of systems thinking skills. Student motivations and attitudes towards the subject of chemistry will also be evaluated via validated survey instruments (Guay et al., 2000; Liu et al., 2017). The learning activities have been designed and developed successfully, though the delivery of the intervention is currently ongoing. Preliminary results indicate that students are excited to learn about how chemistry can be more sustainable, and that they are engaging with the learning activities. The aim of this research is to provide rigorous evidence for using systems thinking as a tool to teach students about green chemistry, ‘future-proofing’ chemistry in a way that is relevant, meaningful, and authentic for today’s chemistry students. Outcomes from our data analysis will help inform the development of new undergraduate chemistry education curricula that align with contemporary sustainable challenges. REFERENCES An, J., Loppnow, G.R., & Holme, T. A. (2021). Measuring the impact of incorporating systems thinking into general chemistry on affective components of student learning. Canadian Journal of Chemistry, 99(8), 698–705. Fisher, M.A. (2019). Systems thinking and educating the heads, hands, and hearts of chemistry majors. Journal of Chemical Education, 96(12), 2715–2719. Guay, F., Vallerand, R. J., & Blanchard, C. (2000). On the assessment of situational intrinsic and extrinsic motivation: The Situational Motivation Scale (SIMS). Motivation and emotion, 24(3), 175–213. Liu, Y., Ferrell, B., Barbera, J., & Lewis, J. E. (2017). Development and evaluation of a chemistry-specific version of the academic motivation scale (AMS-Chemistry). Chemistry Education Research and Practice, 18(1), 191–213. Mahaffy, P. G., Matlin, S. A., Holme, T. A., & MacKellar, J. (2019). Systems thinking for education about the molecular basis of sustainability. Nature Sustainability, 2(5), 362–370. Smith, T. (2011). Using critical systems thinking to foster an integrated approach to sustainability: A proposal for development practitioners. Environment, development and sustainability, 13, 1–17. Wissinger, J. E., Visa, A., Saha, B. B., Matlin, S. A., Mahaffy, P. G., Kümmerer, K., & Cornell, S. (2021). Integrating sustainability into learning in chemistry. Journal of Chemical Education, 98(4), 1061–1063

Large Faraday Rotation in Optical-Quality Phthalocyanine and Porphyrin Thin Films

The magneto-optical phenomenon known as Faraday rotation involves the rotation of plane-polarized light as it passes through an optical medium in the presence of an external magnetic field oriented parallel to the direction of light propagation. Faraday rotators find applications in optical isolators and magnetic-field imaging technologies. In recent years, organic thin films comprised of polymeric and small-molecule chromophores have demonstrated Verdet constants, which measure the magnitude of rotation at a given magnetic field strength and material thickness, that exceed those found in conventional inorganic crystals. We report herein the thin-film magnetic circular birefringence (MCB) spectra and maximum Verdet constants of several commercially available and newly synthesized phthalocyanine and porphyrin derivatives. Five of these species achieved maximum Verdet constant magnitudes greater than 105 deg T–1 m–1 at wavelengths between 530 and 800 nm. Notably, a newly reported zinc(II) phthalocyanine derivative (ZnPc-OT) reached a Verdet constant of −33 × 104 deg T–1 m–1 at 800 nm, which is among the largest reported for an organic material, especially for an optical-quality thin film. The MCB spectra are consistent with resonance-enhanced Faraday rotation in the region of the Q-band electronic transition common to porphyrin and phthalocyanine derivatives, and the Faraday A-term describes the electronic origin of the magneto-optical activity. Overall, we demonstrate that phthalocyanines and porphyrins are a class of rationally designed magneto-optical materials suitable for applications demanding large Verdet constants and high optical quality

Band structures of periodic porphyrin nanostructures

Recent progress in the synthesis of π-conjugated porphyrin arrays of different shapes and dimensionalities motivates us to examine the band structures of infinite (periodic) porphyrin nanostructures. We use screened hybrid density functional theory simulations and Wannier function interpolation to obtain accurate band structures of linear chains, 2D nanosheets and nanotubes made of zinc porphyrins. Porphyrin units are connected by butadiyne (C4) or ethyne (C2) linkers, or “fused” (C0), i.e. with no linker. The electronic properties exhibit strong variations with the number of linking carbon atoms (C0/C2/C4). For example, all C0 nanostructures exhibit gapless or metallic band structures, whereas band gaps open for the C2 or C4 structures. The reciprocal space point at which the gaps are observed also show fluctuations with the length of the linkers. We discuss the evolution of the electronic structure of finite porphyrin tubes, made of a few stacked six-porphyrin rings, towards the behavior of the infinite nanotube. Our results suggest approaches for engineering porphyrin-based nanostructures to achieve target electronic properties

Disentangling global and local ring currents †

Magnetic field-induced ring currents in aromatic and antiaromatic molecules cause characteristic shielding and deshielding effects in the molecules' NMR spectra. However, it is difficult to analyze (anti)aromaticity directly from experimental NMR data if a molecule has multiple ring current pathways. Here we present a method for using the Biot-Savart law to deconvolute the contributions of different ring currents to the experimental NMR spectra of polycyclic compounds. This method accurately quantifies local and global ring current susceptibilities in porphyrin nanorings, as well as in a bicyclic dithienothiophene-bridged [34]octaphyrin. There is excellent agreement between ring current susceptibilities derived from both experimental and computationally-predicted chemical shifts, and with ring currents calculated by the GIMIC method. Our method can be applied to any polycyclic system, with any number of ring currents, provided that appropriate NMR data are available

From macrocycles to quantum rings: Does aromaticity have a size limit?

The ring currents of aromatic and antiaromatic molecules are remarkable emergent phenomena. A ring current is a quantum-mechanical feature of the whole system, and its existence cannot be inferred from the properties of the individual components of the ring. Hückel’s rule states that when an aromatic molecule with a circuit of [4n + 2] π electrons is placed in a magnetic field, the field induces a ring current that creates a magnetic field opposing the external field inside the ring. In contrast, antiaromatic rings with 4n π electrons exhibit ring currents in the opposite direction. This rule bears the name of Erich Hückel, and it grew from his molecular orbital theory, but modern formulations of Hückel’s rule incorporate contributions from others, particularly William Doering and Ronald Breslow. It is often assumed that aromaticity is restricted to small molecular rings with up to about 22 π electrons. This Account outlines the discovery of global ring currents in large macrocycles with circuits of up to 162 π electrons. The largest aromatic rings yet investigated are cyclic porphyrin oligomers, which exhibit global ring currents after oxidation, reduction or optical excitation but not in the neutral ground state. The global aromaticity in these porphyrin nanorings leads to experimentally measurable aromatic stabilization energies in addition to magnetic effects that can be studied by NMR spectroscopy. Wheel-like templates can be bound inside these nanorings, providing excellent control over the molecular geometry and allowing the magnetic shielding to be probed inside the nanoring. The ring currents in these systems are well-reproduced by density functional theory (DFT), although the choice of DFT functional often turns out to be critical. Here we review recent contributions to this field and present a simple method for determining the ring current susceptibility (in nA/T) in any aromatic or antiaromatic ring from experimental NMR data by classical Biot–Savart calculations. We use this method to quantify the ring currents in a variety of aromatic rings. This survey confirms that Hückel’s rule reliably predicts the direction of the ring current, and it reveals that the ring current susceptibility is surprisingly insensitive to the size of the ring. The investigation of aromaticity in even larger molecular rings is interesting because ring currents are also observed when mesoscopic metal rings are placed in a magnetic field at low temperatures. The striking similarity between the ring currents in molecules and mesoscopic metal rings arises because the effects have a common origin: a field-dependent phase shift in the electronic wave function. The main difference is that the magnetic flux through mesoscopic rings is much greater because of their larger areas, so their persistent currents are nonlinear and oscillatory with the applied field, whereas the flux through aromatic molecules is so small that their response is approximately linear in the applied field. We discuss how nonlinearity is expected to emerge in large molecular nanorings at high magnetic fields. The insights from this work are fundamentally important for understanding aromaticity and for bridging the gap between chemistry and mesoscopic physics, potentially leading to new functions in molecular electronics

Data for 'Aromatic and antiaromatic ring currents in a molecular nanoring'

This dataset accompanies the publication: M. D. Peeks, T. D. W. Claridge and H. L. Anderson, âAromatic and antiaromatic ring currents in a molecular nanoringâ, Nature, 2017, http://dx.doi.org/10.1038/nature20798 . The associated publication describes the aromaticity and antiaromaticity of a [6]-porphyrin nanoring as a function of the oxidation state of the nanoring. At the time of publication, these were the largest (anti)aromatic systems reported. The diameter of the [6]-porphyrin nanoring is 2.4 nm. The contents of this supporting dataset are described in the âDATA MAP.txtâ file

Data for 'Aromatic and antiaromatic ring currents in a molecular nanoring'

This dataset accompanies the publication: M. D. Peeks, T. D. W. Claridge and H. L. Anderson, “Aromatic and antiaromatic ring currents in a molecular nanoring”, Nature, 2017, http://dx.doi.org/10.1038/nature20798 . The associated publication describes the aromaticity and antiaromaticity of a [6]-porphyrin nanoring as a function of the oxidation state of the nanoring. At the time of publication, these were the largest (anti)aromatic systems reported. The diameter of the [6]-porphyrin nanoring is 2.4 nm. The contents of this supporting dataset are described in the “DATA MAP.txt” file. Please see DATA MAP.txt for documentation about the dataset

Global Aromaticity and Antiaromaticity in Porphyrin Nanoring Anions

Doping, through oxidation or reduction, is often used to modify the properties of π-conjugated oligomers. In most cases, the resulting charge distribution is difficult to determine. If the oligomer is cyclic and doping establishes global aromaticity or antiaromaticity, then it is certain that the charge is fully delocalized over the entire perimeter of the ring. Here we show that reduction of a six-porphyrin nanoring using decamethylcobaltocene results in global aromaticity (in the 6– state; [90 π]) and antiaromaticity (in the 4– state; [88 π]), consistent with Hückel’s rules. Aromaticity is assigned by NMR spectroscopy and density-functional theory calculations. <br /

Correspondence on “How aromatic are molecular nanorings? The case of a six-porphyrin nanoring”

A recent Research Article in this journal by Matito and co-workers claimed that none of the oxidation states of a butadiyne-linked six-porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. Experimental data from NMR spectroscopy for a whole family of nanorings provide strong evidence for global ring currents. The NMR data reveal these ring currents directly, without needing analysis by density functional theory (DFT). Furthermore, DFT calculations reproduce the experimental results when a suitable functional is used

A Semiconducting Conjugated Radical Polymer: Ambipolar Redox Activity and Faraday Effect

Investigations of magnetism in electronically coupled polyradicals have largely focused on applications in photonic and magnetic devices, wherein radical polymers were found to possess molecularly tunable and cooperative magnetic properties. Radical polymers with nonconjugated insulating backbones have been intensively investigated previously; however the integration of radical species into conducting polymer backbones is at an early stage. We report herein 1,3-bisdiphenylene-2-phenylallyl (BDPA)-based conjugated radical polymers that display ambipolar redox activities and conductivities. Moreover, these radical polymers were demonstrated to be promising magneto-optic (MO) materials with Faraday rotations wherein the sign is modulated by the radical character and display absolute Verdet constants up to (2.80 ± 0.84) × 104 deg T-1 m-1 at 532 nm. These values rival the performance of the present-day commercial inorganic MO materials (e.g., terbium gallium garnet, V = -1.0 × 104 deg T-1 m-1 at 532 nm). The structure property studies detailed herein reveal the promise of multifunctional conjugated radical polymers as responsive MO materials