materials chemistry

ACS LiveSlides: Another Step in Multimedia Science Publishing

Last March I introduced the Hanson research group’s five minute GEOSET videos. I’ve since learned that, in July 2013, Prashant V. Kamat (Deputy Editor), George C. Schatz (Editor-in-Chief) and their co-workers at the Journal of Physical Chemistry Letters announced ACS LiveSlides™, a user friendly mechanism for generating and sharing video slideshows for each manuscript. As noted in their editorial piece, they were motivated by the “changing publication landscape and the wide availability of new electronic tools have made it increasingly important to explore new ways to disseminate published research.”

We recently created an ACS LiveSlides™ presentation for our J. Phys. Chem. Lett. manuscript, “Photon Upconversion and Photocurrent Generation via Self-Assembly at Organic–Inorganic Interfaces.” The paper introduces self-assembled bilayers as a means of facilitating molecular photon upconversion and demonstrates photocurrent generation from the upconverted state. It’s arguably the first example of directly extracting charge from a molecular upconverted state if using the first submission date, first public disclosure, or the patent application date as markers. If using the manuscript acceptance date, Simpson et. al’s publication holds that distinction.

An invitation to create an ACS LiveSlides™ presentation immediately followed the message notifying us that our manuscript was accepted. All we needed to do was provide 5-8 Power Point Slides summarizing the manuscript (using a format provided by the ACS) and record an accompanying <10-minute mp3 audio file. The editors took the files (and a list of times for each slide transitions) and published our LiveSlides™ presentation in less than a week. It was an easy process and now anyone can view our presentation. No subscription necessary.

One drawback is that the video cannot be embedded on a webpage. As stated in their terms:

Files available from the ACS website may be downloaded for personal use only. Users are not otherwise permitted to reproduce, republish, redistribute, or sell any Supporting Information from the ACS website…

So we have a backup plan for those preferring an embedded video. Below you’ll find our GEOSET video summary presented by Sean Hill.

Sharing Science: Distilling Publications Into 5 Minute Videos

Aiming to make our research more accessible, the Hanson research group will post five minute videos recapping each of our papers after they are published. This probably sounds like a very time consuming undertaking, but our group is very lucky to have access to GEOSET studio, a creation of our local Nobelist Harry Kroto.

Harry, a 2006 Nobel Prize winner for the discovery of the Buckminster Fullerene and current faculty member at Florida State University, has been heavily involved in outreach activities encouraging children and public involvement in science. Global Educational Outreach for Science, Engineering and Technology (GEOSET) is one branch of this effort. GEOSET is a free, online service that allows users to upload and view science-related videos. GEOSET videos mirror what students see in a seminar or classroom. Its dual-window format shows side-by-side views of the presenter and his or her presentation slides (or you can click to expand one or the other).

The process for creating a video is very user-friendly. All I need to bring to the GEOSET studio are myself and my presentation slides (quick aside: I don’t mean to underplay what may be a stressful activity for those who are camera-shy. It takes a lot to be a comfortable presenter. Thankfully, GEOSET makes it as easy as possible). The studio camera has a teleprompter that shows your presentation slides as you present. It’s a wonderful set-up that makes it look like you are presenting off the top of your head. After giving your presentation, just like you would at any group meeting, the in-studio software couples the recording with the presentation file and then the GEOSET staff post the video online.

There are numerous partner institutions around the world that have dedicated studios for creating GEOSET videos. At FSU the GEOSET studio is located on campus in the Dirac Library. Any student/faculty/staff can schedule an appointment, bring their presentation file (Keynote, PowerPoint, etc.) and quickly record a video.

The first GEOSET video from our research group is presented by second year graduate student Jamie Wang. Jamie recently published her paper “Modulating Electron Transfer Dynamics at Dye–Semiconductor Interfaces via Self-Assembled Bilayers”, in the Journal of Physical Chemistry C. Her research is focused on controlling electron transfer events at dye-semiconductor interfaces particularly for application in dye-sensitized solar cells.

I want to send a special thanks to Jamie for being the first group member to pioneer this Hanson Research group practice. She did a wonderful job and will serve as a solid example for future videos – a few of which will be available soon.

Explosive Solutions

mercury azides

Instead of starting at the beginning of a paper I want to kick off this commentary with a statement from near the end:

Caution! Covalent azides are potentially hazardous and can decompose explosively under various conditions! Especially Hg2(N3)2, α– and β-Hg(N3)2, and [Hg2N]N3 in this work are extremely friction/shock-sensitive and can explode violently upon the slightest provocation. Appropriate safety precautions (safety shields, face shields, leather gloves, protective clothing) should be taken when dealing with large quantities. Hg compounds are highly toxic! Experimental details can be found in the Supporting Information.”

This wonderful statement appears in a recent publication by Professors Schultz and Villinger at the University of Rostock in Germany. They discuss the preparation of mercury azides and the azide of something called Millon’s Base. This compound was new to me and it turns out to be nitridodimercury hydroxide, [Hg2N]OH.2H2O, which Millon1 discovered by the reaction of mercurous oxide and ammonia in the mid 1800s. In a classic example of understatement the authors’ state that as is the case with most transition metal nitrogen compounds the extremely low energy barriers to explosive decomposition result in difficulties in the isolation and manipulation of said species! Curtius, of rearrangement fame, was apparently the first person to isolate mercury azide Hg2(N3)2 from the reaction of hydrogen azide and mercury2. I guess this was after the discovery of his famous rearrangement.

Structural data for this compound is available from x-ray and revealed two modifications, called α and β. Due to its lability the β modification has not been fully characterised. Schultz etal have now rectified this situation and also report the preparation of the azide salt, [Hg2N]N3 of Millon’s base. They prepared α & β-Hg(N3)2, the latter compound by slow diffusion of aqueous sodium azide into a solution of mercury (II) nitrate separated by a layer of aqueous sodium nitrate. In this synthesis one wonders how any yield was obtained because when the needles of β-Hg(N3)2 begin to form in the lower mercury(II) nitrate layer spontaneous explosions occur during crystal growth. If you want large crystals of either modification, usually obtained by slow crystallisation, I would not recommend it as apparently large crystals seem to explode when you look at them the wrong way, even in solution they detonate. Explosive solutions would be a great name for a company! Anyway, in spite of these difficulties an X-ray structure along with a melting point was obtained.

Turning now to the synthesis of the azide of Millon’s base the authors note that the normal method always produced a mixture of the two modifications. Pure α-[Hg2N]N3 was obtained by treatment of α-[Hg2N]Br with concentrated aqueous sodium azide for 300 days, so you need patience when dealing with these compounds, not only because they are explosive but they suffer from long reaction times. However starting with β-[Hg2N]NO3 the reaction was faster, only taking 4 days for the exchange with azide but produced a mixture of modifications. However, they did manage to obtain both modifications.

Elemental analysis could not be carried out due to their explosive nature and both modifications are sensitive towards heat, shock and especially friction. The bigger the crystal the more sensitive it is. However, slow heating in a DSC instrument showed that they are stable up to 283°C for the β form and 313°C for the α. Rapid heating in a closed vessel caused violent heavy detonation accompanied by a bright blue flash.

The paper has some fascinating x-ray pictures of all the molecules discussed and allowed determination of the N-Hg bond lengths. Together with the chemistry and the dangers involved in this chemistry, a great piece of work has evolved into a wonderful very readable paper. Congratulations to all who participated.

 

References:

1      E. Millon, J. Prakt. Chem. 1839, 16, 58.

2      T. Curtius, Chem. Ber. 1890, 23, 3023

Alexandrite Effect: Not All White Light is Created Equal

Alexandrite is a gem that exhibits an amazing property. It appears red in incandescent light and green in sunlight. Incandescent light and sunlight both appear white when we look at them but, as Alexandrite demonstrates, not all white light is the same. Differences in white light sources can have a profound effect on how we perceive an object’s color. The Alexandrite Effect is a perfect example.

Image 1-compared

Blue, green, and red light are defined by single, specific wavelengths of the electromagnetic spectrum (~470 nm, ~540 nm, and ~650 nm, respectively). In contrast, white light is not a single wavelength. It is the sum of multiple, distinct portions of the visible spectrum. Just as many different numbers can be added together to reach 100 (50 + 50, 33 + 67, 99 + 1, etc.) there are many ways to add colors of “pure” light to make white light.

One of the most common man-made sources of white light is black-body radiation. Metallurgist produce white light via black-body radiation when they heat metal in a furnace.  Similarly, incandescent bulbs generate their glow by passing current across a metal element until it heats up and radiates.  Yet, while black-body radiation is an effective means of producing white light, it is very energetically inefficient (most of the energy input is used to produce infrared light/heat). A much more efficient means of creating white light is to combine a few specific wavelengths of the visible spectrum. The color combinations that produce white light are depicted in the CIE color diagram below.

Image 2 CIE

The colors along the rounded edge of the shape (everything but the bottom, straight edge) can be thought of as “pure” because they’re defined by a specific wavelength of light between 380 and 700 nm.  All colors inside the border as well as along the bottom, straight edge are created when two or more “pure” colors are combined. White light is at the “center” of the CIE diagram (x = 0.33 and y = 0.33).

I regularly referenced this diagram while researching organic light emitting diodes (OLEDs) because molecules emit specific wavelengths of light and are not broad emitters (like heated metal). To make an OLED TV that displays most CIE colors, including white, manufactures incorporate blue (x = 0.1666, y = 0.0089), green (x = 0.2738, y = 0.7174) and red (x = 0.7347, y = 0.2653) emitting molecules in the screen design.  To make an OLED screen appear yellow, both the red and the green molecules must be electronically excited and emit at the same time. The resulting color is entirely dependent on the proportion of red and green molecules excited. Exciting more green than red molecules makes the screen appear greenish-yellow. Exciting more red than green molecules makes it appear reddish-orange. If we want the screen to appear yellow, then the intensities of the emitting red and green molecules must be balanced. These “summed” emission can be depicted by drawing a straight line between the red and green points on the CIE diagram (image below).

Image 3-Yellow CIE

Similar strategies are used to generate different types of white emitting OLEDs. Every day, ambient white light is sometimes created by summing the emissions of blue and yellow emitting molecules (image below left). White pixels on OLED TVs are created by summing red, green and blue emitters (image below right).

Image 4- white light cie

We perceive any light source emitting these two color combinations as white. However, illuminating an object, like alexandrite, under these various white light sources can uncover really interesting color chemistry.

Chrysoberyl is an oxide with the formula BeAl2O4 which is typically colorless or yellow because it absorbs little to no visible light. Alexandrite is the rarest and most valuable member of the chrysoberyl family and is formed when some of the Al3+ is replaced by Cr3+, either naturally or intentionally.

The small amount of Cr3+ impurity in Alexandrite (<1 %) is directly responsible for its interesting colors. This coloration can be depicted via the absorption spectrum below.

Image 5- absorbance spectrum

This absorption spectrum is a graphical depiction of the amount of light absorbed/removed/not transmitted (y-axis) versus the wavelength of light (x-axis). Unlike undoped chrysoberyl, Alexandrite has two strong absorption peaks in the visible spectrum at ~400 nm and ~600 nm (for those of you crystal field junkies, the peaks at ~400 nm and ~600 nm are assigned to the 4A2 to 4T1 and the 4A2 to 4T2 transitions of octahedrally coordinated Cr3+). Conversely, it has two low absorptions, or high transmission windows, in the blue-green (470-520 nm) and red (>650 nm) portions of the spectrum.

When Alexandrite is viewed under uniform white light (the sum of ALL visible wavelengths of light) the blue and yellow portions of visible light are absorbed and the blue-green and red portions are not (below left). This gives the gem a purple-grey–the sum of blue-green and red emission–appearance (below right).

Image 6-full white

But, as I said above, not all white light sources are the same. Even though sunlight appears white if you look directly at it (don’t look directly at it!), it actually has a larger contribution from the blue and green portions of the spectrum. Under sunlight, Alexandrite absorbs yellow and blue. Yet, since more green and blue light is transmitted than red light, the gem appears blue-green, as depicted below.

Image 7- sunlight

In contrast, when Alexandrite is placed under incandescent lights or a candle, which have a larger contribution from the red portion of the spectrum, the gem appears red.

Image 8-Candle light

Based on the absorption spectra above, the Alexandrite effect could be greatly amplified if we viewed it under a two-component, white OLED (or a comparable two-color emitter). We could produce a white OLED by combining light from a ~490 nm and a ~590 nm emitter. When viewed under this light source, I’d expect Alexandrite to be a very sharp cyan color because the amber component (590 nm) would be entirely absorbed.

Image 9-cyan from OLED

The relatively narrow emission of molecular species (50-100 nm) would also likely result in a much sharper color for Alexandrite than what is observed in the sun or under incandescent lights. If anyone has an easy way to perform this experiment, I would love to see the result.

That concludes my lengthy but thorough explanation of the interesting color chemistry of Alexandrite, a gem that is sometimes describes as an “emerald by day, ruby by night.” And maybe, experiment pending, this phrase will one day include “cyan by OLED.”

References

Farrell, E. F.; Newnham, R. E.; The American Mineralogist, 1965, 50, 1972-1981.

Liu, Y.; Shigley, J. E.; Fritsch, E.; Hemphill, S.; Mineralogical Magazine 1995, 59, 111-114.

http://www.alexandrite.net/chapters/chapter5/index.html

http://nature.berkeley.edu/classes/eps2//wisc/Lect7.html