This work was supported by the Chung-Ang University Research Grants in 2019 and the National Research Foundation of Korea (NRF-2020R1C1C1011134).

1.&#160;1H NMR spectrum acquisition at photostationary state (PSS)
<ol>
	<li>In a natural quartz NMR tube containing 4.2 mg (0.01 mmol) of hydrazone switch 1, add 1.0 mL of deuterated dimethyl sulfoxide (DMSO-d6). Transfer half of the solution to another NMR tube.</li>
	<li>Place one of the NMR tubes 1 cm in front of a Xenon arc lamp equipped with a 436 nm bandpass filter. Start irradiation to the NMR sample and record a 1H NMR spectrum every d...

<ol>
	<li>Kathan, M., Hecht, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoswitchable+molecules+as+key+ingredients+to+drive+systems+away+from+the+global+thermodynamic+minimum.">Photoswitchable molecules as key ingredients to drive systems away from the global thermodynamic minimum.</a> Chemical Society Reviews. 46, 5536-5550 (2017).</li><li>Feringa, B. L., Browne, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Molecular Switches. 2nd ed. , (2011).</li><li>Baroncini, M., Silvi, S., Credi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photo-+and+redox-driven+artificial+molecular+motors.">Photo- and redox-driven artificial molecular motors.</a> Chemical Reviews. 120 (1), 200-268 (2020).</li><li>Goulet-Hanssens, A., Eisenreich, F., Hecht, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enlightening+materials+with+photoswitches.">Enlightening materials with photoswitches.</a> Advanced Materials. 32 (20), 1905966 (2020).</li><li>Bas&#237;lio, N., Pischel, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drug+delivery+by+controlling+a+supramolecular+host-guest+assembly+with+a+reversible+photoswitch.">Drug delivery by controlling a supramolecular host-guest assembly with a reversible photoswitch.</a> Chemistry-A European Journal. 22 (43), 15208-15211 (2016).</li><li>Wegener, M., Hansen, M. J., Driessen, A. J. M., Szymanski, W., Feringa, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photocontrol+of+antibacterial+activity:+shifting+from+UV+to+red+light+activation.">Photocontrol of antibacterial activity: shifting from UV to red light activation.</a> Journal of the American Chemical Society. 139 (49), 17979-17986 (2017).</li><li>Izquierdo-Serra, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+control+of+endogenous+receptors+and+cellular+excitability+using+targeted+covalent+photoswitches.">Optical control of endogenous receptors and cellular excitability using targeted covalent photoswitches.</a> Nature Communications. 7 (1), 12221 (2016).</li><li>Mourot, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+optical+control+of+nociception+with+an+ion-channel+photoswitch.">Rapid optical control of nociception with an ion-channel photoswitch.</a> Nature Methods. 9 (4), 396-402 (2012).</li><li>Griffiths, K., Halcovitch, N. R., Griffin, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+solar+energy+storage+under+ambient+conditions+in+a+MOF-based+solid-solid+phase-change+material.">Long-term solar energy storage under ambient conditions in a MOF-based solid-solid phase-change material.</a> Chemistry of Materials. 32 (23), 9925-9936 (2020).</li><li>Sun, C. -. L., Wang, C., Boulatov, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applications+of+photoswitches+in+the+storage+of+solar+energy.">Applications of photoswitches in the storage of solar energy.</a> ChemPhotoChem. 3 (6), 268-283 (2019).</li><li>Gu, M., Zhang, Q., Lamon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomaterials+for+optical+data+storage.">Nanomaterials for optical data storage.</a> Nature Reviews Materials. 1 (12), 16070 (2016).</li><li>Roke, D., Wezenberg, S. J., Feringa, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+rotary+motors:+Unidirectional+motion+around+double+bonds.">Molecular rotary motors: Unidirectional motion around double bonds.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (38), 9423-9431 (2018).</li><li>Stranius, K., B&#246;rjesson, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+the+photoisomerization+quantum+yield+of+photoswitchable+molecules+in+solution+and+in+the+solid+state.">Determining the photoisomerization quantum yield of photoswitchable molecules in solution and in the solid state.</a> Scientific Reports. 7 (1), 41145 (2017).</li><li>Schneider, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long+term+spectral+irradiance+measurements+of+a+1000-watt+xenon+arc+lamp.">Long term spectral irradiance measurements of a 1000-watt xenon arc lamp.</a> NASA-CR. , 132533 (1974).</li><li>Qian, H., Pramanik, S., Aprahamian, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochromic+hydrazone+switches+with+extremely+long+thermal+half-lives.">Photochromic hydrazone switches with extremely long thermal half-lives.</a> Journal of the American Chemical Society. 139 (27), 9140-9143 (2017).</li><li>Shao, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solution+and+solid-state+emission+toggling+of+a+photochromic+hydrazone.">Solution and solid-state emission toggling of a photochromic hydrazone.</a> Journal of the American Chemical Society. 140 (39), 12323-12327 (2018).</li><li>Shao, B., Qian, H., Li, Q., Aprahamian, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+property+analysis+of+the+solution+and+solid-state+properties+of+bistable+photochromic+hydrazones.">Structure property analysis of the solution and solid-state properties of bistable photochromic hydrazones.</a> Journal of the American Chemical Society. 141 (20), 8364-8371 (2019).</li><li>Moran, M. J., Magrini, M., Walba, D. M., Aprahamian, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Driving+a+liquid+crystal+phase+transition+using+a+photochromic+hydrazone.">Driving a liquid crystal phase transition using a photochromic hydrazone.</a> Journal of the American Chemical Society. 140 (42), 13623-13627 (2018).</li><li>Guo, X., Shao, B., Zhou, S., Aprahamian, I., Chen, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+intracellular+particles+and+precise+control+of+drug+release+using+an+emissive+hydrazone+photochrome.">Visualizing intracellular particles and precise control of drug release using an emissive hydrazone photochrome.</a> Chemical Science. 11 (11), 3016-3021 (2020).</li><li>Yang, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+enzymatic+synthesis+of+&#947;-cyclodextrin+using+a+photoremovable+hydrazone+template.">Dynamic enzymatic synthesis of &#947;-cyclodextrin using a photoremovable hydrazone template.</a> Chem. 7 (8), 2190-2200 (2021).</li><li>Yang, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multistage+reversible+Tg+photomodulation+and+hardening+of+hydrazone-containing+polymers.">Multistage reversible Tg photomodulation and hardening of hydrazone-containing polymers.</a> Journal of the American Chemical Society. 143 (40), 16348-16353 (2021).</li><li>Connors, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chemical kinetics : the study of reaction rates in solution. , (1990).</li><li>Shao, B., Qian, H., Li, Q., Aprahamian, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+property+analysis+of+the+solution+and+solid-state+properties+of+bistable+photochromic+hydrazones.">Structure property analysis of the solution and solid-state properties of bistable photochromic hydrazones.</a> Journal of the American Chemical Society. 141 (20), 8364-8371 (2019).</li><li>Kuhn, H., Braslavsky, S., Schmidt, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+actinometry+(IUPAC+technical+report).">Chemical actinometry (IUPAC technical report).</a> Pure and Applied Chemistry. 76 (12), 2105-2146 (2004).</li><li>Murov, S. L., Carmichael, I., Hug, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of hotochemistry 2nd ed. Rev. And expanded. , (1993).</li><li>D&#252;rr, H., Bouas-Laurent, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Photochromism: Molecules and Systems. , (2003).</li><li>Kl&#225;n, P., Wirz, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Photochemistry of Organic Compounds: From Concepts to Practice. , (2009).</li><li>Harris, J. D., Moran, M. J., Aprahamian, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+molecular+switch+architectures.">New molecular switch architectures.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (38), 9414-9422 (2018).</li><li>Maafi, M., Brown, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+kinetic+model+for+AB(1&#981;)+systems:+A+closed-form+integration+of+the+differential+equation+with+a+variable+photokinetic+factor.">The kinetic model for AB(1&#981;) systems: A closed-form integration of the differential equation with a variable photokinetic factor.</a> Journal of Photochemistry and Photobiology A: Chemistry. 187, 319-324 (2007).</li><li>Lahikainen, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunable+photomechanics+in+diarylethene-driven+liquid+crystal+network+actuators.">Tunable photomechanics in diarylethene-driven liquid crystal network actuators.</a> ACS Applied Materials &amp; Interfaces. 12 (42), 47939-47947 (2020).</li><li>Mallo, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochromic+switching+behaviour+of+donor-acceptor+Stenhouse+adducts+in+organic+solvents.">Photochromic switching behaviour of donor-acceptor Stenhouse adducts in organic solvents.</a> Chemical Communications. 52, 13576-13579 (2016).</li><li>Feldmeier, C., Bartling, H., Riedle, E., Gschwind, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LED+based+NMR+illumination+device+for+mechanistic+studies+on+photochemical+reactions+-+Versatile+and+simple,+yet+surprisingly+powerful.">LED based NMR illumination device for mechanistic studies on photochemical reactions - Versatile and simple, yet surprisingly powerful.</a> Journal of Magnetic Resonance. 232, 39-44 (2013).</li></ol>

Various strategies to tune the spectral and switching properties of photoswitches have been developed, and the register of photoswitches is rapidly expanding28. It is thus crucial to correctly determine their photophysical properties, and we anticipate the methods summarized in this article will be a helpful guide to experimenters. Provided that the thermal relaxation rate is very slow at room temperature, measurement of PSS compositions at different irradiation wavelengths, molar attenuation coef...

Photochromic organic molecules have attracted considerable attention in a wide range of scientific disciplines as light is a unique stimulus that can drive a system away from its thermodynamic equilibrium non-invasively1. Irradiation of light with appropriate energies allows structural modulation of photoswitches with high spatiotemporal precision2,3,4. Thanks to these advantages, various types of photoswitches based on configurational isomerization of the double bonds (e.g., stilbenes, azobenzenes, imines, fumaramides, thioindigos) and ring opening/closure (e.g., spiropyrans, dithienylethenes, fulgides, donor-acceptor Stenhouse adducts) have been developed and utilized as the core components of adaptive materials at various length scales. Representative applications of photoswitches involve photochromic materials, drug delivery, switchable receptors and channels, information or energy storage, and molecular machines5,6,7,8,9,10,11,12. In most studies presenting newly designed photoswitches, their photophysical properties such as &#955;max of absorption and emission, molar attenuation coefficient (&#949;), fluorescence lifetime, and photoisomerization quantum yield are characterized thoroughly. The investigation of such properties provides key information on the electronic states and transitions that are crucial for understanding the optical properties and isomerization mechanism.
However, accurate measurement of photoisomerization quantum yield-the number of photoisomerization events that occurred divided by the number of photons at the irradiation wavelength absorbed by the reactant-is often complicated in a typical laboratory setting due to several reasons. Determination of the photoisomerization quantum yield is generally achieved by monitoring the advancement of reaction and measuring the number of absorbed photons during irradiation. The primary concern is that the amount of photon absorption per unit time changes progressively because the total absorption by the solution changes over time as the photochemical reaction proceeds. Therefore, the number of consumed reactants per unit time depends on the time section in which it is measured during the irradiation. Thus, one is obliged to estimate the photoisomerization quantum yield that is defined differentially.
A more troublesome problem arises when both the reactant and photoproduct absorb light at the irradiation wavelength. In this case, the photochemical isomerization occurs in both directions (i.e., a photoreversible reaction). The two independent quantum yields for the forward and backward reactions cannot be obtained directly from the observed reaction rate. Inaccurate light intensity is also a common cause of error. For example, the aging of the bulb gradually changes its intensity; irradiance of the Xenon arc lamp at 400 nm decreases by 30% after 1000 h of operation14. The spreading of non-collimated light makes the actual incident irradiance significantly smaller than the nominal power of the source. Thus, it is crucial to accurately quantify the effective photon flux. Of note, thermal relaxation of the metastable form at room temperature should be sufficiently small to be ignored.
This paper introduces a set of procedures to determine the photoisomerization quantum yield of a bistable photoswitch. A number of hydrazone photoswitches developed by the group of Aprahamian, the pioneering research team in the field, have been in the spotlight thanks to their selective photoisomerization and remarkable stability of their metastable isomers15,16,17. Their hydrazone photoswitches comprise two aromatic rings joined by a hydrazone group, and the C=N bond undergoes selective E/Z isomerization upon irradiation at appropriate wavelengths (Figure 1). They have been successfully incorporated as the motile components of dynamic molecular systems18,19,20,21. In this work, we prepared a new hydrazone derivative bearing amide groups and investigated its photoswitching properties for the determination of the photoisomerization quantum yield.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1,10-phenanthroline</td>
			<td>Sigma-Aldrich</td>
			<td>131377-2.5G</td>
			<td></td>
		</tr>
		<tr>
			<td>340 nm bandpass filter, 25 mm diameter, 10 nm FWHM</td>
			<td>Edmund Optics</td>
			<td>#65-129</td>
			<td></td>
		</tr>
		<tr>
			<td>436 nm bandpass filter, 25 mm diameter, 10 nm FWHM</td>
			<td>Edmund Optics</td>
			<td>#65-138</td>
			<td></td>
		</tr>
		<tr>
			<td>Anhydrous sodium acetate</td>
			<td>Alfa aesar</td>
			<td>A13184.30</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>Samchun</td>
			<td>D1138</td>
			<td>HPLC grade</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide-d6</td>
			<td>Sigma-Aldrich</td>
			<td>151874-25g</td>
			<td></td>
		</tr>
		<tr>
			<td>Gemini 2000; 300 MHz NMR spectrometer</td>
			<td>Varian</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>H2SO4</td>
			<td>Duksan</td>
			<td>235</td>
			<td></td>
		</tr>
		<tr>
			<td>Heating bath</td>
			<td>JeioTech</td>
			<td>CW-05G</td>
			<td></td>
		</tr>
		<tr>
			<td>MestReNova 14.1.1</td>
			<td>Mestrelab Research S.L., https://mestrelab.com/</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Natural quartz NMR tube</td>
			<td>Norell</td>
			<td>S-5-200-QTZ-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium ferrioxalate trihydrate</td>
			<td>Alfa aesar</td>
			<td>31124.06</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz absorption cell</td>
			<td>Hellma</td>
			<td>HE.110.QS10</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-VIS spectrophotometer</td>
			<td>Scinco</td>
			<td>S-3100</td>
			<td></td>
		</tr>
		<tr>
			<td>Xenon arc lamp</td>
			<td>Thorlabs</td>
			<td>SLS205</td>
			<td>Fiber adapter was removed</td>
		</tr>
	</tbody>
</table>

determination of the photoisomerization quantum yield of a hydrazone photoswitch

Photoswitching organic molecules that undergo light-driven structural transformations are key components to construct adaptive molecular systems, and they are utilized in a wide variety of applications. In most studies employing photoswitches, several important photophysical properties such as maximum wavelengths of absorption and emission, molar attenuation coefficient, fluorescence lifetime, and photoisomerization quantum yield are carefully determined to investigate their electronic states and transition processes. However, measurement of the photoisomerization quantum yield, the efficiency of photoisomerization with respect to the absorbed photons, in a typical laboratory setting is often complicated and prone to error because it requires the implementation of rigorous spectroscopic measurements and calculations based on an appropriate integration method. This article introduces a set of procedures to measure the photoisomerization quantum yield of a bistable photoswitch using a photochromic hydrazone. We anticipate that this article will be a useful guide for the investigation of bistable photoswitches that are being increasingly developed.

Upon irradiation of 1 in an NMR tube with 436 nm light (Z:E = 54:46 in the initial state), the proportion of 1-E increases due to the dominant Z-to-E isomerization of the hydrazone C=N bond (Figure 1). The isomeric ratio can be readily obtained from the relative signal intensities of distinct isomers in the 1H NMR spectrum (Figure 2). After 5 days of irradiation at 436 nm, the sampl...

Watch this Scientific Journal Video about Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch at JoVE.com

Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch

Photoisomerization quantum yield is a fundamental photophysical property that should be accurately determined in the investigation of newly developed photoswitches. Here, we describe a set of procedures to measure the photoisomerization quantum yield of a photochromic hydrazone as a model bistable photoswitch.

Photoswitching organic molecules that undergo light-driven structural transformations are key components to construct adaptive molecular systems, and they ...

Here we explain a set of protocols for precise measurement of the photoisomerization quantum yield of a photochromic hydrazone as a model photoswitching molecule. The methods introduced here can be applied to other families of bi-stable photoswitches. Protocols for photoswitches with different for photo-physical properties and their selection guidelines are provided in the supplementary information.To begin, place the NMR sample at the distance of one centimeter in front of a xenon arc lamp equipped with a 436-nanometer band pass filter and start irradiation. Record a proton NMR spectrum every day till there is no exchange in the spectra as switch one reaches PSS. For another NMR sample, irradiate the solution using a 340-nanometer band pass filter and record the NMR spectrum as described previously.Open FID files of the NMR spectra at the PSSs with NMR processing software. Integrate a distinctive set of peaks of the distinct isomers and calculate the isomeric ratios. Place the prepared sample at the distance of one centimeter in front of a xenon arc lamp equipped with a 436-nanometer band pass filter and start irradiation.Measure the UV-visible absorption spectrum every two hours until there is no change in the spectra as switch one reaches PSS. For another sample, irradiate the solution using a 340-nanometer band pass filter and measure the UV visible spectrum at PSS in the same way. Deduce the absorbance spectra of the pure 1-Z and 1-E isomers and calculate their molar attenuation coefficients at all wavelengths as described in the text.Heat the silicon oil filled in a heating bath circulator to 131 degrees Celsius and check whether the temperature of the bath is stabilized. Submerge two NMR sample tubes in the heating bath. After one hour of heating, transfer the NMR tubes quickly to a dry ice bath to pause the thermal relaxation caused by latent heat.Thaw the NMR samples at room temperature and ensure dimethyl sulfoxide is defrosted. Then, record the proton NMR spectra of the samples. Again perform the heating and thawing process and record the proton NMR spectra of the samples until there is no change in the proton NMR spectra as switch one reaches thermodynamic equilibrium.Open FID files of the NMR spectra obtained in the course of heating and calculate the concentration of 1-E based on the total sample concentration and the isomeric ratio. Then, plot the averaged concentration of 1-E as a function of the heating time. Perform an exponential fit to the data to obtain the rate constant of thermal relaxation, K, using the equation as described in the text.Plot natural log of K versus reciprocal of T.Perform a linear fit according to the Arrhenius equation as described in the text to extrapolate the rate constant at room temperature and calculate the thermal half-life of 1-E at room temperature using the equation as described in the text. In a 20-milliliter glass vial containing 29.48 milligrams of potassium ferrioxalate trihydrate, add eight milliliters of deionized water. Add one milliliter of 0.5 molar aqueous sulfuric acid to the ferrioxalate solution and dilute to 10 milliliters with deionized water to prepare a 0.006 molar ferrioxalate in 0.05 molar aqueous sulfuric acid solution.In another 20-milliliter glass vial containing 10 milligrams of 1, 10-phenanthroline and 1.356 grams of anhydrous sodium acetate, add 10 milliliters of 0.1 molar aqueous sulfuric acid to make a buffered 0.1%phenanthroline solution. Measure the UV-visible absorption spectrum of the ferrioxalate solution. Determine the fraction of absorbed light at 340 and 436 nanometers using the absorbances of the ferrioxalate solution as described in the text.Place the quartz cuvette containing the ferrioxalate solution one centimeter in front of the xenon arc lamp equipped with a 436-nanometer band pass filter. Start irradiation to the sample for 90 seconds. After irradiation, add 0.35 milliliters of the phenanthroline solution and a magnetic bar into the cuvette, followed by stirring for one hour in the dark to form a ferroin complex.Prepare a quartz cuvette containing two milliliters of non-irradiated ferrioxalate solution and 0.35 milliliters of the phenanthroline solution as a non-irradiated sample. Measure the UV-visible absorption difference between the non-irradiated and irradiated samples. Repeat the procedure for sample preparation and measurement of the UV-visible absorption spectrum described previously with a 340-nanometer band pass filter.Calculate the molar photon flux arriving at the cuvette using this equation. Place the prepared sample one centimeter in front of the xenon arc lamp equipped with a 436-nanometer band pass filter and start irradiation. Measure the UV-visible absorption spectrum with different intervals until there is no change in the spectra as switch one reaches PSS.Once reaching PSS, recover the cuvette from the UV-Vis spectrophotometer and irradiate the solution using a 340-nanometer band pass filter. Measure UV-visible absorption spectrum as described previously. From the obtained UV-Vis absorption spectra, calculate the values of photokinetic factor Ft using the observed absorbances at the irradiation wavelengths.Calculate the unidirectional quantum yields for Z to E and E to Z photoisomerization processes. Upon irradiation at 436 nanometers, the proportion of 1-E increases due to the dominant Z to E isomerization of the hydrazone CN double bond. The isomeric ratio was obtained from the relative signal intensities of distinct isomers in the 1H NMR spectrum.At 436 nanometers, the sample shows 92%of 1-E, while at 340 nanometers, 82%of 1-Z was found. The ismomeric ratios and UV-Vis absorption spectra at PSS are used to deduce the UV-Vis spectra of the pure 1-Z and 1-E isomers. These spectra of the pure isomers suggest that the incomplete photoisomerization is attributed to the reverse photochemical process.For determining the photoisomerization quantum yield, measurement of the E to Z thermal relaxation rate and the effective molar photon flux is required. The rate constant of thermal relaxation extrapolated from the Arrhenius plot was very small at room temperature, and thus, the effect of thermal relaxation in the photoisomerization process could be ignored. The effective molar photon flux arriving at the sample was obtained from ferrioxalate actinometry and the pseudo-quantum yield of photoisomerization at the irradiation wavelength can be calculated.Finally, the unidirectional quantum yields for Z to E and E to Z photoisomerization processes can be calculated from the pseudo-quantum yields. For determination of the photoisomerization quantum yield, it is essential to obtain precise values of the thermal relaxation rate at room temperature and the effective molar photon flux. For those who deal with bi-stable photoswitches other than hydrazones, it is important to use the proper integration method for the photokinetic factor, which is explained in the supplementary information.

determination-photoisomerization-quantum-yield-hydrazone

Research

JoVE Journal

Chemistry

3.1K visualizações.  Chung-Ang University. Aqui explicamos um conjunto de protocolos para medição precisa do rendimento quântico fotoisomerização de uma hidrato fotocrômica como uma molécula de fotochromia modelo. Os métodos introduzidos aqui podem ser aplicados a outras famílias de fotosvais bi-estáveis. Protocolos para fotos com diferentes para propriedades fotofísiais e suas diretrizes de seleção são fornecidos nas informações complementares.Para começar, coloque a amostra de NMR à distância de um centíme...