Photochromic and Electrochromic Diimide ... - ACS Publications

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Photochromic and Electrochromic Diimide Synthesized Simply from Inexpensive Compounds: A Multidisciplinary Experiment for Undergraduate Students Taleb Abdinejad,† Mohammad R. Zamanloo,*,† Taher Alizadeh,‡ Nosrat O. Mahmoodi,§ and Shima Rahim Pouran† †

Department Department 14155-6455, § Department

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‡

of Applied Chemistry, Faculty of Basic Science, University of Mohaghegh Ardabili, Ardabil, Iran of Analytical Chemistry, Faculty of Chemistry, University College of Science, University of Tehran, P.O. Box Tehran, Iran of Chemistry, Faculty of Science, University of Guilan, P.O. Box 41335-1914, Rasht, Iran

S Supporting Information *

ABSTRACT: An interdisciplinary laboratory experiment was designed and carried out on the basis of the photo/ electrochromism of N,N′-bis(cysteine)pyromellitic diimide (BCPD), suitable for organic chemistry laboratory I and physical chemistry laboratory II students. In the organic chemistry laboratory, students synthesized BCPD and studied its photo/electrochromic properties briefly. In the physical chemistry laboratory, students were asked to explore the photo/ electrochemistry of the synthesized dimide through the use of various techniques such as UV−vis spectroscopy, cyclic voltammetry, and conductometry measurements. By conducting this experiment, students not only learned the basic chemical concepts and techniques, such as photo/electrochemistry of imides, the use of reflux technique in organic synthesis, UV−vis spectroscopy, and cyclic voltammetry, but also perceived the interdisciplinary nature of chemistry research. Altogether, this experiment was designed to engage students in chemistry by connecting education to real-life situations, as well as indicating that their products in organic chemistry laboratory are valuable compounds. KEYWORDS: Upper-Division Undergraduate, Organic Chemistry, Physical Chemistry, Hands-On Learning/Manipulatives, Kinetics, UV−Vis Spectroscopy, Photochemistry, Electrochemistry

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INTRODUCTION

chemistry laboratory in other courses, such as a physical chemistry laboratory, shows the value of crude products to students. This is the best way to avoid the “synthesize and discard” fashion, which is common in most traditional organic chemistry laboratories.7 Although aromatic imides are less reactive than most organic functional groups, they are well-known as high-strength polymers,14 electrochromic materials for electrochromic devices,15 and selective gas permeation membranes.16 The photo/electrochemistry of imides has been extensively investigated in the past several years.17−20 It has turned out that the electron transfer to the imide carbonyl group, leading to the benzyl-type radical intermediate, is responsible for the observed outcomes in both photo- and electrostimulated reactions (Scheme 1). Despite such vast studies, there is a dearth of information regarding educational experiments with imides, probably due to their time-consuming synthesis.

In recent years, establishing connections between chemistry education and real-life situations as well as developing eyecatching chemical reactions have been used as efficient strategies to engage students in chemistry and to increase their interest.1,2 In this regard, photo- and electrochromic compounds are good choices not only for their amazing color changes (induced by light and electrical potential, respectively), but also because of their real-world applications in smart windows,3 displays,4 sunglasses,5 etc. Recently, we developed an interdisciplinary experiment involving a simple and inexpensive synthesis of N,N′-bis(cysteine)pyromellitic diimide (BCPD), followed by the identification of its photo/ electrochromic properties, for organic and physical chemistry laboratories. The use of interdisciplinary experiments provides an opportunity for undergraduates to perceive the incorporation and relationship between various fields of science to generate new knowledge or to solve the existing problems.6−8 Hence, considerable attention has been geared toward designing novel interdisciplinary experiments.9−13 More importantly, using the synthesized compounds from an organic © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: July 19, 2017 Revised: June 13, 2018

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DOI: 10.1021/acs.jchemed.7b00540 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

S6). Synthesis and characterization of BCPD were performed in the organic chemistry laboratory to introduce concepts and skills including the chemistry of imides, stoichiometry, reflux, filtration, melting point, and recrystallization. Also, students gained primary experience about photo/electrochromic phenomena (a necessary background for the next laboratory course) by irradiating an acidic solution of BCPD and preparing a simple electrochromic device. In the physical chemistry laboratory, they learned about the kinetics of firstorder reactions, photo/electrochromism (with special emphasize on the photo/electrochromism of imides), UV−vis spectroscopy, cyclic voltammetry, and intrinsically electrochromic phenomena through investigating the photo/electrochemisty of the diimide saved from the organic chemistry laboratory. Detailed descriptions of the experiments in the two courses are in the Supporting Information, pages S8−S17 and S19−S29.

Scheme 1. Electrocoloration and Photocoloration Mechanisms in Aromatic Imides

Our newly published results on the photo/electrochromic characteristics of BCPD21 encouraged us to use it in educational context. Some encouraging characteristics are as follows: • The dimide can be synthesized simply from inexpensive materials within an hour (Scheme 2).

Organic Chemistry Laboratory

In the organic chemistry laboratory, students worked in groups of two or three. This part of the experiment was carried out in three laboratory sessions (including one 90 min and two 120 min laboratory periods). In the first laboratory session, a definite amount of cysteine (0.5−1 g) was given to each group, and students calculated and weighed the needed amount of pyromellitic dianhydride (PMDA) to react with cysteine. The reflux system was set up, and the two reactants were added to a round-bottom flask. After vigorous refluxing for 1 h, the system was turned off (if there is no time limitation, gentle reflux for 4−6 h is preferred to obtain a higher yield). In the second laboratory session, the crude product was filtered, dried (in an oven), and characterized by determining the melting point and recording the infrared spectrum. The crystallization step was carried out in the third session. Photo/electrochromic properties were investigated briefly by exposing an acidic solution of BCPD to sunlight and preparing a simple electrochromic device (using a commercial power supply, two pieces of fluorine-doped tin oxide (FTO) glass as electrodes, dimethylformamide (DMF) as solvent, and tetrabutylammonium hexafluorophosphate (TBAPF6) as electrolyte, respectively).

Scheme 2. Synthesis of Photo/Electrochromic Diimide

• It possesses both photo- and electrochromic properties (Supporting Information, Figure S3). • Its reaction with organic bases produces salts categorized as intrinsically electrochromic materials. This provides an opportunity to discuss intrinsically electrochromic materials, as well as the role of electrolyte in electrochromic devices (Scheme S1 and Figure S4). • The photocoloration process can be accomplished in daylight (no need for a UV lamp). • T-type photochromism of BCPD provides an opportunity to introduce the concepts of first-order kinetics. • The value of oxidation/reduction potential and the potential-induced changes in spectroscopic properties are solvent-dependent. Previously, several laboratory experiments have been published in this Journal, either to teach photochromism or electrochromism, or to employ photochromism or electrochromism as a means to instruct basic chemical concepts such as chemical kinetics, UV−vis spectroscopy, and electrochemistry.22−25 However, to the best of our knowledge, the present study is the first to introduce both electrochromism and photochromism in a single experiment. This report discusses an experiment that was designed and performed to • Engage students in chemistry using interesting reactions, connecting education to real-life situations, and reusing the compounds from one laboratory in other laboratories • Highlight the interdisciplinary nature of chemistry research • Teach the key concepts and skills of organic and physical chemistry such as photo/electrochemistry of imides, chemical kinetics, etc.

Physical Chemistry Laboratory

In the physical chemistry laboratory, students were teamed with two in each group. This part of the experiment was completed over two lab sessions, each 2 h in duration. Initially, after short instruction on how to use a UV−vis spectrophotometer and other required instruments, the UV−vis spectra of BCPD (dissolved in sulfuric acid) were collected before and after exposure to sunlight (by students under the supervision of an instructor). Afterward, the order of the back (colorbleaching) reaction and its rate constant were determined using the data collected from the decay of the visible band at 604 nm. Students measured the temperature of the lab before collecting kinetics data because the bleaching reaction is dependent on temperature. In the second laboratory session, after a short introduction to cyclic voltammetry, students collected the voltammograms of BCPD dissolved in different solvents (sulfuric acid and DMF) using a three-electrode system (two platinum wires as working and counter electrodes, as well as a standard calomel electrode (SCE) as a reference electrode). Simultaneous with potential sweeping, students traced the changes in the color of the working electrode. For the DMF solution, the voltammogram was collected once in

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EXPERIMENTAL SECTION Necessary data and notes for conducting of experiment are provided for instructors (Supporting Information, pages S2− B




Figure 1. (a) Recording the absorption of blue species (produced by exposing to sunlight) vs time. (b) UV−vis absorption spectra of BCPD before/after exposure to light, and corresponding color changes. (c) ln(Abs) vs time for the color-bleaching reaction of BCPD.

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the absence of electrolyte and once in the presence of electrolyte. Thereafter, students investigated the intrinsic electrochromism of a BCPD/organic base mixture by measuring conductivity of BCPD, imidazole (or any organic base such as butylamine, propylamine, etc.), and a BCPD/ imidazole mixture in DMF solution, followed by collecting their voltammograms. Finally, the chromogenic reaction of BCPD with active metals was analyzed by adding a drop of the acidic solution of BCPD on sanded and unsanded aluminum foils.

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RESULTS AND DISCUSSION

Organic Chemistry Laboratory

To date, this component of the experiment has been completed three times by 48 students, with 15−17 students enrolled in each laboratory class. Some results obtained by students in the organic chemistry laboratory are in the Supporting Information, pages S31−S32. The calculation method applied by students to obtain the amount of needed PMDA to react with cysteine showed that most of the students do not use the dimensional analysis method in stoichiometry calculations (even at the undergraduate level). However, most groups obtained the correct answer. The analysis of students’ laboratory reports and attached data showed that, except recrystallization, all of the 48 students successfully fulfilled the requested tasks. All groups were able to synthesize BCPD with crude yields ranging from 53% to 61% when the mixture was vigorously refluxed for 1 h (literature value21 is 68% for 10 h reflux). In two of the three laboratory classes, gentle refluxing for 6 h was performed to obtain higher yields (65−68% crude yields). During the second laboratory session, the mixture was filtered, dried, and characterized by determination of melting point and by infrared spectroscopy. The reported melting points by students (recorded in an organic laboratory report sheet) ranged from 264 to 270 °C, which is in good agreement with the melting point reported in the literature21 (267−269 °C). In the case of IR spectroscopy, all groups successfully recorded an IR spectrum, assigned dominant peaks (1778− 1780 cm−1 related to imide CO, 2555−2575 cm−1 related to SH, and 2500−3400 cm−1 related to OH of COOH), and attached it to the laboratory report sheet (Figure S17). During the third laboratory session, each student examined the solubility of BCPD in various organic solvents (Table S6),

HAZARDS

In the chemistry laboratory, all chemicals should be considered as dangerous to the body, and precautions must be taken when working with them. Students must wear a lab coat, safety goggles, and gloves all of the time. Although sulfuric acid is one of the most common compounds in chemistry laboratories, its concentrated solution is extremely corrosive and can cause serious and irreversible damage upon contact with the skin or eyes. Accordingly, it should be handled under the surveillance of the instructor. Pyromellitic dianhydride is harmful. The inhalation of its dust, especially during weighing processes, can cause respiratory irritation. The use of open flames should be highly limited in the organic chemistry laboratory because the vapor of organic solvents is very flammable. The most safe and simplest methods include heating with oil or using a water bath heater. Though imides are known to be unreactive compounds, BCPD should be used with caution and treated as hazardous due to its unknown hazards. C




Figure 2. (a) Preparation of simple electrochromic device. (b) Reaction of sanded and unsanded aluminum foil with acidic solution of BCPD. (c) Voltammogram of BCPD recorded in sulfuric acid. Platinum wire is used as working and counter electrodes. SCE is the reference electrode.

identical in all lab sessions). The comparisons showed lower rate constants at low temperatures. The second lab session was allocated to investigate the electrochromic properties of BCPD. All students successfully collected the voltammograms of BCPD in different solvents (sulfuric acid and DMF) and applied them to extract the electrochemical properties of BCPD (Figure 2 and pages S34− S35 of Supporting Information). By tracing the color changes at the cathodic electrode, during potential sweep, students correctly recognized that the electrochromism of BCPD is reduction-type. The comparison of the voltammograms of BCPD recorded in different solvents, as well as corresponding changes in the color of the cathodic electrode during potential sweep, allowed students to understand the role of the solvent in electrochromism of BCPD. To introduce intrinsic electrochromism, students prepared DMF solutions of BCPD (0.08 M) and imidazole (0.14 M). After measuring the conductivity of the prepared solutions and recording their voltammograms, students performed the same actions for their mixture. The conductivities obtained for BCPD and imidazole solutions ranged from 4 to 20 and from 6 to 25 μs, respectively. The conductivity was significantly increased upon mixing the solutions (150−220 μs), indicating an increase in ionic species due to an acid−base reaction. As was expected, due to poor conductivity, the potential scanning of BCPD and imidazole solutions did not produce a voltammogram. The necessity of suitable conductivity of a solution to collect a voltammogram and attain an electrocoloration provided an opportunity for students to understand the role of electrolytes in electrochromic devices. In the final step, students set up a simple electrochromic system using a BCPD/imidazole mixture, commercial power supply, Pt wires, FTO glass, and other necessary tools. Also, they examined the reaction of BCPD with various metals. With little help from the instructor, all groups were able to prepare the mentioned electrochromic device (Figure 2a). Approximately 86% of the students correctly explained the observed color changes for the reaction of BCPD with active metals (Figure 2b) such as aluminum,

tried to recrystallize it (Table S7), and explored its photo/ electrocoloration. Of the 48 students, only 26 (58%) were able to recrystallize the crude product. Conversations with unsuccessful groups showed that two factors, too fast cooling of the solution and using an inappropriate ratio of solvents, were the main reasons for the failures. The analysis of students’ explanations, written in the “more explanation” part of the organic laboratory report sheet (Table S8), showed that the final part of experiment (photo/electrocoloration) was the most interesting. Nearly all groups included the description of photo/electrocoloration in their explanations. They used words such as interesting, attractive, and amazing in their description, indicating the success of the experiment in increasing their interest. Examples of student explanations are provided in Supporting Information. Physical Chemistry Laboratory

To date, this part of the experiment has been carried out two times by 30 students with 14−16 students enrolled in each laboratory class. In the physical chemistry laboratory, due to the instrumental limitations, all experiments were performed in rotation. Some results obtained by students in the physical chemistry laboratory are in the Supporting Information, pages S33−S35. In the first laboratory session, the UV−vis spectra of BCPD were collected before and after exposure to sunlight (Figure 1b) using a scanning UV−vis spectrophotometer (Figure S9). Next, students obtained the order of the back reaction (color-bleaching) and its rate constant using a single beam spectrophotometer adjusted to 604 nm (Figure 1a,c). To do this, they exposed an acidic solution of BCPD to sunlight (for a definite time) and recorded A604 versus time. All of the students successfully collected the UV−vis spectra before and after irradiation. Moreover, all groups also correctly identified that the color-bleaching reaction is first-order and determined its rate constant. The rate constants obtained ranged from 0.0011 to 0.0037 s−1. The dependency of the rate constant on temperature was easily detectable by comparing the rate constant values obtained under various temperatures (because of the changes in climate, the temperature of the lab was not D



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ACKNOWLEDGMENTS Authors gratefully acknowledge financial support by University of Mohaghegh Ardabili.

zinc, etc. This indicates the students’ ability to apply their learning to explain new phenomena. To further assess students’ learning, they answered a number of questions, labeled as “postlab questions” (Supporting Information, pages 36−39, for questions, answers and the percentage of correct answers to each question) related to this experiment in the next laboratory session. The evaluation of the responses to the questions implied their satisfaction with the experiment. All of them agreed to conduct similar experiments in other subjects. Furthermore, the results showed that the students were able to remember what they had learned in organic laboratory. For example, in response to the question related to synthesis of the imide (question 1 in part 1 of postlab questions, page S36), all students used the correct amine and anhydride in their synthesis design. Such good learning retention could be considered one of the advantages associated with interdisciplinary experiments as compared with discipline-specific education.7,26,27 The comparison of students’ understanding and skills before (based on their answers to prelab questions, initial conversations with them, and observing their performances in laboratory) and after (based on students’ answers to postlab questions, their lab-reports, and observing their performances in laboratory) conducting the experiment showed significant progress in all learning goals (Table S11).

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CONCLUSION In this interdisciplinary laboratory experiment, students in organic chemistry laboratory I successfully synthesized and characterized an aromatic diimide. Then, they performed an elementary investigation on photo/electrochromic properties of the synthesized diimide. In physical chemistry laboratory II, students reused the diimide saved from the organic laboratory to perform a comprehensive investigation of its photo/ electrochromic properties. The laboratory reports of the students and their answers to postlab questions showed that they learned basic concepts and acquired the necessary skills. Through these experiments, students not only had an opportunity to observe the interdisciplinary nature of chemistry but also perceived the value of their product in organic chemistry laboratory. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00540. Listing of materials, equipment, precautions, prelab and postlab examination questions, notes for instructor, student handouts, and samples of student experimental results (PDF, DOCX) Video of photocoloration (AVI) Video of electrocoloration (AVI)

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Mohammad R. Zamanloo: 0000-0002-1569-221X Notes

The authors declare no competing financial interest. E




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Photochromic and Electrochromic Diimide ... - ACS Publications

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