This work was supported in part by grants-in-aid KAKENHI from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) Japan (#26104539, #26620020, #26810011, #15H03766, #15KT0060, #16H00826, and #16K13927); the Konica Minolta Science and Technology Foundation; the "Planting Seeds for Research" program of TokyoTech; the Imaging Science Project of the Center for Novel Science Initiatives (CNSI) at the National Institutes of Natural Sciences (NINS) (#IS261006); the RIKEN-IMS joint program on "Extreme Photonics;" and the Consortium for Photon Science and Technology (CPhoST).

<ol>
	<li>Stapelfeldt, H., Constant, E., Sakai, H., Corkum, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-resolved+Coulomb+explosion+imaging:+A+method+to+measure+structure+and+dynamics+of+molecular+nuclear+wave+packets.">Time-resolved Coulomb explosion imaging: A method to measure structure and dynamics of molecular nuclear wave packets.</a> Phys. Rev. A. 58, 426-433 (1998).</li><li>Hishikawa, A., Matsuda, A., Fushitani, M., Takahashi, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+Recurrently+Migrating+Hydrogen+in+Acetylene+Dication+by+Intense+Ultrashort+Laser+Pulses.">Visualizing Recurrently Migrating Hydrogen in Acetylene Dication by Intense Ultrashort Laser Pulses.</a> Phys. Rev. Lett. 99, 258302 (2007).</li><li>L&#233;gar&#233;, F., 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=Laser+Coulomb-explosion+imaging+of+small+molecules.">Laser Coulomb-explosion imaging of small molecules.</a> Phys. Rev. A. 71, 013415 (2005).</li><li>Stapelfeldt, H., Seideman, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloquium:+Aligning+molecules+with+strong+laser+pulses.">Colloquium: Aligning molecules with strong laser pulses.</a> Rev. Mod. Phys. 75, 543-557 (2003).</li><li>Ohshima, Y., Hasegawa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coherent+rotational+excitation+by+intense+nonresonant+laser+fields.">Coherent rotational excitation by intense nonresonant laser fields.</a> Int. Rev. Phys. Chem. 29, 619-663 (2010).</li><li>Kitano, K., Hasegawa, H., Ohshima, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+Angular+Momentum+Orientation+by+Linearly+Polarized+Laser+Fields.">Ultrafast Angular Momentum Orientation by Linearly Polarized Laser Fields.</a> Phys. Rev. Lett. 103, 223002 (2009).</li><li>Fleischer, S., Khodorkovsky, Y., Prior, Y., Averbukh, I. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+the+sense+of+molecular+rotation.">Controlling the sense of molecular rotation.</a> New J. Phys. 11, 105039 (2009).</li><li>Korobenko, A., Milner, A. A., Milner, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+Observation,+Study,+and+Control+of+Molecular+Superrotors.">Direct Observation, Study, and Control of Molecular Superrotors.</a> Phys. Rev. Lett. 112, 113004 (2014).</li><li>Rosca-Pruna, F., Vrakking, M. J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Revival+structures+in+picosecond+laser-induced+alignment+of+I2+molecules.+I.+Experimental+results.">Revival structures in picosecond laser-induced alignment of I2 molecules. I. Experimental results.</a> J. Chem. Phys. 116, 6567-6578 (2002).</li><li>Dooley, P. W., 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=Direct+imaging+of+rotational+wave-packet+dynamics+of+diatomic+molecules.">Direct imaging of rotational wave-packet dynamics of diatomic molecules.</a> Phys. Rev. A. 68, 023406 (2003).</li><li>Mizuse, K., Kitano, K., Hasegawa, H., Ohshima, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+unidirectional+rotation+directly+imaged+with+molecules.">Quantum unidirectional rotation directly imaged with molecules.</a> Sci. Adv. 1, 1400185 (2015).</li><li>Lin, K., 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=Visualizing+molecular+unidirectional+rotation.">Visualizing molecular unidirectional rotation.</a> Phys. Rev. A. 92, 013410 (2015).</li><li>Korobenko, A., Hepburn, J. W., Milner, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+nondispersing+classical-like+molecular+rotation.">Observation of nondispersing classical-like molecular rotation.</a> Phys. Chem. Chem. Phys. 17, 951-956 (2015).</li><li>Whitaker, B. 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> Imaging in Molecular Dynamics. , (2003).</li><li>Ullrich, J., 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=Recoil-ion+and+electron+momentum+spectroscopy:+reaction-microscopes.">Recoil-ion and electron momentum spectroscopy: reaction-microscopes.</a> Rep. Prog. Phys. 66, 1463 (2003).</li><li>Lee, S. K., 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=Coincidence+ion+imaging+with+a+fast+frame+camera.">Coincidence ion imaging with a fast frame camera.</a> Rev Sci Instrum. 85, 123303 (2014).</li><li>Lee, S. K., 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=Communication:+Time-+and+space-sliced+velocity+map+electron+imaging.">Communication: Time- and space-sliced velocity map electron imaging.</a> J. Chem. Phys. 141, 221101 (2014).</li><li>John, J. J., 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=PImMS,+a+fast+event-triggered+monolithic+pixel+detector+with+storage+of+multiple+timestamps.">PImMS, a fast event-triggered monolithic pixel detector with storage of multiple timestamps.</a> Journal of Instrumentation. 7, 8001 (2012).</li><li>Nomerotski, 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=Pixel+Imaging+Mass+Spectrometry+with+fast+and+intelligent+Pixel+detectors.">Pixel Imaging Mass Spectrometry with fast and intelligent Pixel detectors.</a> Journal of Instrumentation. 5, 07007 (2010).</li><li>Luria, K., Christen, W., Even, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+and+Propagation+of+Intense+Supersonic+Beams.">Generation and Propagation of Intense Supersonic Beams.</a> J. Phys. Chem. A. 115, 7362-7367 (2011).</li><li>Eppink, A. T. J. B., Parker, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Velocity+map+imaging+of+ions+and+electrons+using+electrostatic+lenses:+Application+in+photoelectron+and+photofragment+ion+imaging+of+molecular+oxygen.">Velocity map imaging of ions and electrons using electrostatic lenses: Application in photoelectron and photofragment ion imaging of molecular oxygen.</a> Rev. Sci. Instrum. 68, 3477-3484 (1997).</li><li>Gebhardt, C. R., Rakitzis, T. P., Samartzis, P. C., Ladopoulos, V., Kitsopoulos, T. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Slice+imaging:+A+new+approach+to+ion+imaging+and+velocity+mapping.">Slice imaging: A new approach to ion imaging and velocity mapping.</a> Rev. Sci. Instrum. 72, 3848 (2001).</li><li>St&#246;hr, 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> NEXAFS Spectroscopy. , 132 (1992).</li><li>Siders, C. W., Siders, J. L. W., Taylor, A. J., Park, S. -. G., Weiner, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+High-Energy+Pulse-Train+Generation+Using+a+2+n-Pulse+Michelson+Interferometer.">Efficient High-Energy Pulse-Train Generation Using a 2 n-Pulse Michelson Interferometer.</a> Appl. Opt. 37, 5302-5305 (1998).</li><li>Pitzer, 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=Direct+Determination+of+Absolute+Molecular+Stereochemistry+in+Gas+Phase+by+Coulomb+Explosion+Imaging.">Direct Determination of Absolute Molecular Stereochemistry in Gas Phase by Coulomb Explosion Imaging.</a> Science. 341, 1096-1100 (2013).</li><li>Rakitzis, T. P., Samartzis, P. C., Kitsopoulos, T. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observing+the+symmetry+breaking+in+the+angular+distributions+of+oriented+photofragments+using+velocity+mapping.">Observing the symmetry breaking in the angular distributions of oriented photofragments using velocity mapping.</a> J. Chem. Phys. 111, 10415 (1999).</li><li>Chang, B. -. Y., Hoetzlein, R. C., Mueller, J. A., Geiser, J. D., Houston, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+two-dimensional+product+imaging:+The+real-time+ion-counting+method.">Improved two-dimensional product imaging: The real-time ion-counting method.</a> Rev. Sci. Instrum. 69, 1665 (1998).</li><li>Wiley, W. C., McLaren, I. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-of-Flight+Mass+Spectrometer+with+Improved+Resolution.">Time-of-Flight Mass Spectrometer with Improved Resolution.</a> Rev. Sci. Instrum. 26, 1150 (1955).</li><li>Townsend, D., Minitti, M. P., Suits, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+current+slice+imaging.">Direct current slice imaging.</a> Rev. Sci. Instrum. 74, 2530 (2003).</li><li>Wu, G., 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=A+new+crossed+molecular+beam+apparatus+using+time-sliced+ion+velocity+imaging+technique.">A new crossed molecular beam apparatus using time-sliced ion velocity imaging technique.</a> Rev. Sci. Instrum. 79, 094104 (2008).</li><li>Treacy, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+pulse+compression+with+diffraction+gratings.">Optical pulse compression with diffraction gratings.</a> Quantum Electronics, IEEE Journal of. 5, 454-458 (1969).</li><li>D&#246;rner, R., 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=Cold+Target+Recoil+Ion+Momentum+Spectroscopy:+a+'momentum+microscope'+to+view+atomic+collision+dynamics.">Cold Target Recoil Ion Momentum Spectroscopy: a 'momentum microscope' to view atomic collision dynamics.</a> Physics Reports. 330, 95-192 (2000).</li><li>Herwig, P., 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=Imaging+the+Absolute+Configuration+of+a+Chiral+Epoxide+in+the+Gas+Phase.">Imaging the Absolute Configuration of a Chiral Epoxide in the Gas Phase.</a> Science. 342, 1084-1086 (2013).</li><li>Suzuki, Y. -. I., Suzuki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Linear+and+circular+dichroism+in+photoelectron+angular+distributions+caused+by+electron+correlation.">Linear and circular dichroism in photoelectron angular distributions caused by electron correlation.</a> Phys. Rev. A. 91, 053413 (2015).</li></ol>

The authors have nothing to disclose.

The present procedure enables us to capture a real-time movie of molecular rotation with a slit-based 2D imaging setup. Because the observed ions pass through the slit, step 1.5 is one of the critical steps. The edges of the slit blades must be sharp. When there is a small defect, such as a 0.3 mm dent in the slit, a scratch is observed in the ion image (Figure 6). In such a case, the slit blade should be polished with 2,000-grit wet sandpaper.
Apart from the unique camera angle shown in Figure 1, this method has several advantages over the 3D imaging detector, which was previously the only solution for rotational wave packet imaging.
First, in the present procedure, optical beam alignment can be carried out easily by monitoring raw ion images, as in steps 4.1-4.2. Figure 7 shows the raw camera image at the optimized pump-probe overlap condition. When the pump-probe beam overlap is lost, anisotropic or enhanced image signatures cannot be seen, as in Figure 4A. This fact emphasizes the importance of steps 4.1-4.2 in the present method. Because the spot sizes of the pump and probe beams are on the order of 10 &#181;m, it is generally difficult to find an optimal overlap condition without monitoring real-time images. In the case of a 3D imaging detector, several seconds are required to form an image with sufficient data points (at least 1,000 ions) when a 1,000 Hz or lower repetition-rate laser is employed, because the count rate is limited to a few events per laser shot in the 3D detector. In the present method, on the other hand, the count rate is essentially unlimited, and the number of ions per frame can be increased simply by extending the exposure time. In the present case, more than 1,000 ions are detected within the 50 ms exposure time.
The high count rate of the present method also leads to a shorter data acquisition time. Because the frame rate of the camera is 250 fps, it takes only ~40 s to take one snapshot of the molecular motion at a particular time. For the measurement over the one molecular rotational revival time (~8.4 ps) with a ~33-fs step, the measurement time is only a few hours. This is another advantage, because experimental data would be degraded by the limited long-term stability of the lasers and the entire experimental setup. In our setup, for example, time duration changes with time, partly due to the temperature change in the fs amplifier. A 3-K change within 6 h resulted in the thermal expansion of the amplifier, including the elongation of the distance between the pulse compressor gratings, leading to the elongation of the pulse duration31. Laser-beam drift, which degrades the signal of the pump-induced dynamics, was also detected within ~8 h, although the origin of this drift was not identified.
The present technique is a type of 2D imaging, limiting the information in 3D. In the case of a Coulomb explosion, only the fragment of ions ejected in the detection plane contribute to the image. This implies that it is difficult to apply the present method directly to complicated fragmentation processes, such as those involved in coincidence imaging studies25,32,33. We note that the sum of the signal intensity with our method is proportional to the probability in the detection plane. This represents indirect information on the dimension not included in the imaging plane11,12.
While we focus on Coulomb explosion imaging in this paper, the present approach can be, in principle, applied to general charged-particle imaging, such as that involved in photodissociation studies14. In the existing imaging procedure, to obtain a 2D tomogram of a 3D Newton sphere of charged particles, the polarization of light should be parallel to the detector surface. In other words, the camera angle is limited to particular conditions. Also, in the present 2D imaging technique, a 3D ion cloud is spatially sliced to a 2D cut and is then imaged. With this slice imaging, the freedom of the camera angle will open a way to obtain hitherto-unobserved information that sometimes appears in the laser propagation direction26,34.

For a deeper understanding and better use of the dynamic nature of molecules, it is essential to clearly visualize molecular motions of interest. Time-resolved Coulomb explosion imaging is one of the powerful approaches to achieve this objective1,2,3. In this approach, the molecular dynamics of interest are initiated by a pump ultrashort laser field and are then probed by a time-delayed probe pulse. Upon probe irradiation, molecules are multiply ionized and broken into fragment ions due to the Coulomb repulsion. The spatial distribution of the ejected ions is a measure of the molecular structure and spatial orientation at the probe irradiation. A sequence of measurement scanning the pump-probe delay time leads to the creation of a molecular movie. It is noteworthy that, for the simplest case &#8211; diatomic molecules &#8211; the angular distribution of the ejected ions directly reflects the molecular axis distribution (i.e., the squared rotational wave function).
With regard to the pump process, recent progress in the coherent control of molecular motion using ultrashort laser fields has led to the creation of highly controlled rotational wave packets4,5. Furthermore, the direction of rotation can be actively controlled by using a polarization-controlled laser field6,7,8. It has therefore been expected that a detailed picture of molecular rotation, including wave natures, could be visualized when the Coulomb explosion imaging technique is combined with such a pump process9,10,11,12,13. However, we sometimes encounter experimental difficulties associated with the existing imaging methods, as mentioned below. The purpose of this paper is to present a new way of overcoming these difficulties and of creating a high-quality movie of molecular rotational wave packets. The first experimental movie of molecular rotation taken with the present method, along with its physical implications, were presented in our previous paper11. The background of development, the detailed theoretical aspect of the present imaging technique, and a comparison with other existing techniques will be given in a forthcoming paper. Here, we will mainly focus on the practical and technical aspects of the procedure, including the combination of the typical pump-probe optical setup and the new imaging apparatus. As in the previous paper, the target system is unidirectionally rotating nitrogen molecules11.
The main experimental difficulty of the existing imaging setup, schematically shown in Figure 1, has to do with the position of the detector, or the camera angle. Because the rotational axis coincides with the laser propagation axis6,7,8 in laser-field-induced molecular rotation, it is not practical to install a detector along the rotational axis. When the detector is installed so as to avoid laser irradiation, the camera angle corresponds to a side observation of rotation. In this case, it is impossible to reconstruct the original orientation of molecules from the projected (2D) ion image14. A 3D imaging detector14,15,16,17,18,19, with which the arrival time to the top detector and the ion impact positions can be measured, offered a unique way to directly observe molecular rotation using Coulomb explosion imaging10,12. However, the acceptable ion counts per laser shot are low (typically &#60; 10 ions) in the 3D detector, meaning that it is difficult to create a long movie of molecular motion with high image quality14. The dead time of the detectors (typically ns) also affects the image resolution and imaging efficiency. It is also not a simple task to make a good pump-probe beam overlap by monitoring a real-time ion image with a laser repetition rate of &#60;~1 kHz. Although several groups have observed rotational wave packets using the 3D technique, the spatial information was limited and/or direct, and a detailed visualization of wave nature, including complicated nodal structures, was not achieved10,12.
The essence of the new imaging technique is the use of the &#34;new camera angle&#34; in Figure 1. In this configuration, laser beam exposure to a detector is avoided while the 2D detector is parallel to the rotational plane, leading to the observation from the rotational axis direction. The slit allows only the ion in the rotational plane (the polarization plane of the laser pulses) to contribute to an image. A 2D detector, which offers a higher count rate (typically ~100 ions) than a 3D detector, can be used. The setup of the electronics is simpler than in the case of 3D detection, while the measurement efficiency is higher. Time-consuming mathematical reconstruction, such as Abel inversion14, is also not needed to extract angular information. These features lead to the easy optimization of the measurement system and to the production of high-quality movies. A standard 2D/3D charged-particle imaging apparatus can be easily modified to the present setup without the use of expensive equipment.

<table border="0" cellpadding="0" cellspacing="0" width="618">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">CMOS camera</td>
			<td style="width:83px;">Toshiba TELI</td>
			<td style="width:119px;">BU-238M-ES</td>
			<td style="width:167px;">equipped with SONY IMX174 sensor</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">High voltage switch</td>
			<td style="width:83px;">Behlke</td>
			<td style="width:119px;">HTS-41-03-GSM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">High voltage switch</td>
			<td style="width:83px;">Behlke</td>
			<td style="width:119px;">HTS-80-03</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Digital delay generator</td>
			<td style="width:83px;">Stanford research systems</td>
			<td style="width:119px;">DG535</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Digital delay generator</td>
			<td style="width:83px;">Stanford research systems</td>
			<td style="width:119px;">DG645</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Microchannel plate</td>
			<td style="width:83px;">Photonis</td>
			<td align="right" style="width:119px;">3075</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Pulsed valve</td>
			<td style="width:83px;">LAMID LTD</td>
			<td style="width:119px;">Even-Lavie valve&#160;</td>
			<td style="width:167px;">High repetition, room temperature model</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:249px;">Molecular beam skimmers</td>
			<td style="width:83px;">Institute for Molecular Science</td>
			<td style="width:119px;">13C11</td>
			<td style="width:167px;">3 and 1.5 mm center hole, 25 degrees full inner angle, and ~50 mm length</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Optical Comparator</td>
			<td style="width:83px;">Nikon</td>
			<td style="width:119px;">V-24B</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">DPSS laser</td>
			<td style="width:83px;">Lighthouse Photonics</td>
			<td style="width:119px;">Sprout</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Femtosecond Ti:Sapphire oscillator</td>
			<td style="width:83px;">KMLabs</td>
			<td style="width:119px;">Halcyon</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Femtosecond Ti:Sapphire amplifier</td>
			<td style="width:83px;">Quantronix</td>
			<td style="width:119px;">Odin-II HE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Motorized linear stage</td>
			<td style="width:83px;">Sigma Koki</td>
			<td style="width:119px;">KST(GS)-100X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Manual X-stage</td>
			<td style="width:83px;">Sigma Koki</td>
			<td style="width:119px;">TSD-601S</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">High resolution mirror mount</td>
			<td style="width:83px;">Newport</td>
			<td style="width:119px;">Suprema SX100-F2KN-254</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">High resolution mirror mount</td>
			<td style="width:83px;">LIOP-TEC GmbH</td>
			<td style="width:119px;">SR100-100R-2-HS</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:249px;">Polarization checker</td>
			<td style="width:83px;">Paradigm Devices, Inc.</td>
			<td style="width:119px;">O-tool VIS</td>
			<td></td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:249px;">Instrument communication interface</td>
			<td style="width:83px;">National Instruments</td>
			<td style="width:119px;">NI-MAX</td>
			<td></td>
		</tr>
		<tr height="45">
			<td height="45" style="height:45px;width:249px;">Graphical development environment for measurement programs</td>
			<td style="width:83px;">National Instruments</td>
			<td style="width:119px;">LabVIEW 2014</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">CVI/LEO</td>
			<td style="width:119px;">TLM2-400/800-45UNP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">Altechna</td>
			<td colspan="2">Low GDD Ultrafast mirror</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:249px;">Laser line dielectric mirror</td>
			<td style="width:83px;">Altechna</td>
			<td colspan="2">Low GDD Ultrafast mirror</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:249px;">Femtosecond polarizer</td>
			<td style="width:83px;">Advanced Thin Films</td>
			<td style="width:119px;">PBS-GVD</td>
			<td></td>
		</tr>
	</tbody>
</table>

direct imaging of laser-driven ultrafast molecular rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

Figure 4A shows a probe-only raw image of the N2+ ion ejected upon probe irradiation (Coulomb explosion), taken for one probe laser shot. Each bright spot corresponds to one ion. Figure 4B shows a summed image of 10,000 binarized raw camera images. These images show that our imaging setup can monitor the molecules of all the orientation angles in the polarization plane. Figure 4C shows the normalized polar plot corresponding to that of Figure 4B. Because the rotational control (pump) pulse was absent, the distribution is isotropic (Figure 4C shows a circle).


In Figure 4B, a small defect due to detector inhomogeneity can be seen in the bottom of the ellipse. Such a defect always appears in the same position of the image. Therefore, it can be compensated for by normalizing the observed images with a probe-only image (step 4.5.3.7).
Figure 5 shows selected snapshots taken after the irradiation of the two pump pulses. So as to improve understanding, not only the observed ion images, but also the corresponding polar plots and &#34;dumbbell&#34; model pictures are shown as a function of probe time. The polar plots are created in step 4.5.3.5. The dumbbell picture is an overlapped image of dumbbells of various orientation angles, and their weights (opacity) are the observed angular probabilities. The sequence of images forms a clear movie of unidirectional molecular rotation. The wave nature of motion can be seen as the complicated nodal structures and the dispersion, including an &#34;X&#34;-shape formation.
Figure 6 shows an ion image taken with a damaged slit and a photograph of the slit edge with a dent. A small defect largely affects the observed image. In such a case, repeating step 1.5 is required. This fact is also discussed in the discussion section.
Figure 7 shows the raw camera image at the optimized pump-probe overlap condition. By monitoring such a beam overlap signal, the optical paths can be optimized. This leads to a clear movie, as in Figure 5.
<img alt="Figure 1" src="/files/ftp_upload/54917/54917fig1.jpg" /> 
Figure 1: Conceptual diagram of the camera angles in the impractical, typical, and new configurations. In the typical camera angle, a detector is installed to avoid laser exposure, but the ejection angles of ions cannot be reconstructed from the 2D projected image. In the present, new camera angle, the rotational plane (laser polarization plane) is parallel to the detector surface and is therefore suitable for visualizing the rotational motion. Typical bias voltages are 2,500 V, 1,799 V, 1,846 V, 253 V, 0 V, 3,500 V, -800 V, and 4,500 V for ion optics 1, 2, 3, 4, and 5, the pulsed repeller, the microchannel plates, and the phosphor screen, respectively. The ion optics numbering starts at the bottom electrode. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54917/54917fig2.jpg" /> 
Figure 2: Schematic diagrams of the 2D imaging unit. (A) Schematic diagram of the detector assembly. A circle plate colored in orange is a baseplate to which the other parts are mounted with bolts. (B) Schematic diagram of the slit assembly. The right picture explains the motion of the slit. The size values are in mm. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54917/54917fig3.jpg" /> 
Figure 3: Schematic diagram of the present pump-probe optical setup. The optical paths of the pump pulses for rotational excitation are illustrated by the red lines, while that of the probe (imaging) pulse is shown by the blue line. NLC, nonlinear crystal for second-harmonic generation; HWP, half-waveplate; QWP, quarter-waveplate; DM, dichroic mirror; BS, 50:50 beam splitter; HRM: high-resolution mirror mount. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54917/54917fig4.jpg" /> 
Figure 4: Raw and analyzed Coulomb exploded ion images. (A) A typical raw image of N2+ taken for one probe shot. (B) Summed image for 10,000 binarized camera images. The size of the camera image is 1,200 x 750 pixels. The corresponding real-space size is 80 mm x 50 mm. (C) The normalized polar plot constructed from the summed image. In the raw and summed images, false color was added to show the signal intensity. The polar angles in degrees are shown along the circumference. The radial value is an angle-dependent probability (arbitrary unit). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54917/54917fig5.jpg" /> 
Figure 5: Selected snapshots of the laser-induced rotational wave packet dynamics. In each time delay, the upper panel shows the ion image in which the elliptical shape has been converted to a circle. The middle panel shows the corresponding polar plot. The bottom panel shows a dumbbell model of the angular distribution. This dumbbell picture is an overlapped image of dumbbells from various orientation angles, and their weights (opacity) are the observed angular probabilities. The polar plot uses the same unit and scale as in Figure 4. The ion image employs transformed coordinates, as in step 4.5.3.4. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/54917/54917fig6.jpg" /> 
Figure 6: Effect of the slit defect on the experimental ion image. (A) Observed probe-only N2+ ion image taken with a damaged slit. (B) Photograph of the slit edge having a sub-mm dent. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/54917/54917fig7.jpg" /> 
Figure 7: Raw camera image at the optimized pump-probe overlap condition. The probe time is set at t = 4.0 ps after the first pump pulse irradiation. At this time, the maximum degree of molecular alignment is achieved. The size of the camera image is 1,200 x 750 pixels. The corresponding real-space size is 80 mm x 50 mm. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54917/54917fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Direct Imaging of Laser-driven Ultrafast Molecular Rotation at JoVE.com

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

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9.6K Views.  Tokyo Institute of Technology. We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

Video: Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Synthesis of Immunotargeted Magneto-plasmonic Nanoclusters

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications including contrast enhancement in novel magnetomotive imaging modalities, simultaneous capture&#160;and detection of circulating tumor cells (CTCs),&#160;and multimodal molecular imaging combined with photothermal therapy of cancer cells. These applications have stimulated significant interest in development of protocols for synthesis of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared (NIR) region and a strong magnetic moment. Here, we present a novel protocol for synthesis of such hybrid nanoparticles that is based on an oil-in-water microemulsion method. The unique feature of the protocol described herein is synthesis of magneto-plasmonic nanoparticles of various sizes from primary blocks which also have magneto-plasmonic characteristics. This approach yields nanoparticles with a high density of magnetic and plasmonic functionalities which are uniformly distributed throughout the nanoparticle volume. The hybrid nanoparticles can be easily functionalized by attaching antibodies through the Fc moiety leaving the Fab portion that is responsible for antigen binding available for targeting.

Here, we describe a protocol for synthesis of magneto-plasmonic nanoparticles with a strong magnetic moment and a strong near-infrared (NIR) absorbance. The protocol also includes antibody conjugation to the nanoparticles through the Fc moiety for various biomedical applications which require molecular specific targeting.

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications ...

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered &#39;random&#39;. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

We describe an experiment designed to probe the electronic damage induced in nanocrystals of Buckminsterfullerene (C60) by intense, femtosecond pulses of X-rays. The experiment found that, surprisingly, rather than being stochastic, the X-ray induced electron dynamics in C60 are highly correlated, extending over hundreds of unit cells within the crystals1.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the ...

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The devices are patterned from epoxy glue using soft lithography and are suitable for in situ X-ray diffraction experiments at room temperature. The sample wells are lidded on both sides with polymeric polyimide foil windows that allow diffraction data collection with low X-ray background. This fabrication method is undemanding and inexpensive. After the sourcing of a SU-8 master wafer, all fabrication can be completed outside of a cleanroom in a typical research lab environment. The chip design and fabrication protocol utilize capillary valving to microfluidically split an aqueous reaction into defined nanoliter sized droplets. This loading mechanism avoids the sample loss from channel dead-volume and can easily be performed manually without using pumps or other equipment for fluid actuation. We describe how isolated nanoliter sized drops of protein solution can be monitored in situ by dynamic light scattering to control protein crystal nucleation and growth. After suitable crystals are grown, complete X-ray diffraction datasets can be collected using goniometer based in situ fixed target serial X-ray crystallography at room temperature. The protocol provides custom scripts to process diffraction datasets using a suite of software tools to solve and refine the protein crystal structure. This approach avoids the artefacts possibly induced during cryo-preservation or manual crystal handling in conventional crystallography experiments. We present and compare three protein structures that were solved using small crystals with dimensions of approximately 10-20 &#181;m grown in chip. By crystallizing and diffracting in situ, handling and hence mechanical disturbances of fragile crystals is minimized. The protocol details how to fabricate a custom X-ray transparent microfluidic chip suitable for in situ serial crystallography. As almost every crystal can be used for diffraction data collection, these microfluidic chips are a very efficient crystal delivery method.

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes in detail how to fabricate and operate microfluidic devices for X-ray diffraction data collection at room temperature. Additionally, it describes how to monitor protein crystallization by dynamic light scattering and how to process and analyze obtained diffraction data.

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The ...

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

Automation of a Positron-emission Tomography (PET) Radiotracer Synthesis Protocol for Clinical Production

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological targets and processes. However, the increasing number of different tracers creates challenges for their production at radiopharmacies. While historically it has been practical to dedicate a custom-configured radiosynthesizer and hot cell for the repeated production of each individual tracer, it is becoming necessary to change this workflow. Recent commercial radiosynthesizers based on disposable cassettes/kits for each tracer simplify the production of multiple tracers with one set of equipment by eliminating the need for custom tracer-specific modifications. Furthermore, some of these radiosynthesizers enable the operator to develop and optimize their own synthesis protocols in addition to purchasing commercially-available kits. In this protocol, we describe the general procedure for how the manual synthesis of a new PET tracer can be automated on one of these radiosynthesizers and validated for the production of clinical-grade tracers. As an example, we use the ELIXYS radiosynthesizer, a flexible cassette-based radiochemistry tool that can support both PET tracer development efforts, as well as routine clinical probe manufacturing on the same system, to produce [18F]Clofarabine ([18F]CFA), a PET tracer to measure in vivo deoxycytidine kinase (dCK) enzyme activity. Translating a manual synthesis involves breaking down the synthetic protocol into basic radiochemistry processes that are then translated into intuitive chemistry &#34;unit operations&#34; supported by the synthesizer software. These operations can then rapidly be converted into an automated synthesis program by assembling them using the drag-and-drop interface. After basic testing, the synthesis and purification procedure may require optimization to achieve the desired yield and purity. Once the desired performance is achieved, a validation of the synthesis is carried out to determine its suitability for the production of the radiotracer for clinical use.

Automation of a Positron-emission Tomography PET Radiotracer Synthesis Protocol for Clinical Production

Positron-emission tomography (PET) imaging sites that are involved in multiple early clinical research trials need robust and versatile radiotracer manufacturing capabilities. Using the radiotracer [18F]Clofarabine as an example, we illustrate how to automate the synthesis of a radiotracer using a flexible, cassette-based radiosynthesizer and validate the synthesis for clinical use.

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological ...

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces are demonstrated. This work requires careful design, considerable synthetic effort, and proper analysis. The rotary motion of the molecular motor in solution is shown by 1H NMR and UV-vis absorption spectroscopy techniques. In addition, the method to graft the motor onto an amine-coated quartz is described. This method helps to gain more insight into molecular machines.

The manuscript describes how to synthesize and graft a molecular motor on surfaces for single molecular imaging.

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces ...

Imaging Corrosion at the Metal-Paint Interface Using Time-of-Flight Secondary Ion Mass Spectrometry

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS), illustrating that SIMS is a suitable technique to study the chemical distribution at a metal-paint interface. The painted Al alloy coupons are immersed in a salt solution or exposed to air only. SIMS provides chemical mapping and 2D molecular imaging of the interface, allowing direct visualization of the morphology of the corrosion products formed at the metal-paint interface and mapping of the chemical after corrosion occurs. The experimental procedure of this method is presented to provide technical details to facilitate similar research and highlight pitfalls that may be encountered during such experiments.

Time-of-flight secondary ion mass spectrometry is applied to demonstrate the chemical mapping and corrosion morphology at the metal-paint interface of an aluminum alloy after being exposed to a salt solution compared with a specimen exposed to air.

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...

Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals

In this work, we describe a protocol for a novel application of hyperspectral imaging (HSI) in the analysis of luminescent lanthanide (Ln3+)-based molecular single crystals. As representative example, we chose a single crystal of the heterodinuclear Ln-based complex [TbEu(bpm)(tfaa)6] (bpm=2,2&#8217;-bipyrimidine, tfaa&#8211; =1,1,1-trifluoroacetylacetonate) exhibiting bright visible emission under UV excitation. HSI is an emerging technique that combines 2-dimensional spatial imaging of a luminescent structure with spectral information from each pixel of the obtained image. Specifically, HSI on single crystals of the [Tb-Eu] complex provided local spectral information unveiling variation of the luminescence intensity at different points along the studied crystals. These changes were attributed to the optical anisotropy present in the crystal, which results from the different molecular packing of Ln3+ ions in each one of the directions of the crystal structure. The HSI herein described is an example of the suitability of such technique for spectro-spatial investigations of molecular materials. Yet, importantly, this protocol can be easily extended for other types of luminescent materials (such as micron-sized molecular crystals, inorganic microparticles, nanoparticles in biological tissues, or labelled cells, among others), opening many possibilities for deeper investigation of structure-property relationships. Ultimately, such investigations will provide knowledge to be leveraged into the engineering of advanced materials for a wide range of applications from bioimaging to technological applications, such as waveguides or optoelectronic devices.

Here, we present a protocol to obtain luminescent hyperspectral imaging data and to analyze optical anisotropy features of lanthanide-based single crystals using a Hyperspectral Imaging System.