 Thank you very much. And I should start by thanking Steve. Thanks very much for the opportunity to speak here today. When I accepted your invitation last year, I did so based on hope that I would have something to say. We just started the group last year. But I'm glad to say that thanks to the dedicated effort of a really great team of co-workers, we actually have things to talk about today. So my group is a synthetic chemistry group. We make new materials. And the theme behind our work is to make hybrid materials that have molecules as a part, so integrated at the atomic level with extended solids. And the reasoning behind this is quite simple. Solution state molecular chemists will often sing the praises of molecules. So in terms of precisely knowing what you have in terms of structural definition, it's very hard to beat a molecular system, so a zero-dimensional system. We also have decades of synthetic chemistry knowledge, just through organic and metal-organic chemistry. And we are able to fine-tune the structure of molecules at a level of precision that we just cannot attain with solids. So for example, we can change a hydrogen atom to a fluorine atom at a specific carbon on an alkyl chain. We cannot yet do this with solids. But also we are aware of the shortcomings of molecules. We know, for example, that solids have far superior thermal properties, mechanical strength. We know that solids have far more varied electronic structures. So instead of making compromises and choosing to work with molecules or working with solids, we envision hybrid materials that have components that behave like molecules and also have some spatial extension and have components that behave like solids. So we try to make these materials as a single-phase material. And by this, I mean that we don't work with heterogeneous mixtures. We want one material that has components that behave like molecules and has components that behave like solids. So when I started my group last year, I wanted to start on somewhat familiar territory. So as an undergraduate student, I worked in Bob Carver's group at Princeton on metal oxide perovskites. And for my graduate and first doctoral work, I moved to a different world. I worked on molecules and solution state chemistry, so now that I'm back with solids, I still wanted to start with a familiar material. So instead of looking at metal oxide perovskites that require temperatures of about 1,500 degrees to synthesize, these are not conditions amenable for using organic groups, we looked at metal hairline perovskites that can be formed at room temperature. So I just want to take you very briefly through the perovskite structure. You can think of this as a negative framework comprised of metal hairline polyhedra. So each octahedron here has a divalent metal, so a 2-plus metal center at the center of each octahedron. And this is coordinated to six ligands, six bridging ligands. In this case, it's a hairline. So X can be chloride, bromide, or iodide. So this forms an extended 3D framework with a negative charge, and we need to add positive ions for charge neutrality, and these positive ions are denoted as A plus here, and these just sit in a cavity defined by eight of these octahedron. So this is solid state chemists and physicists have done many varied things with perovskites, but we wanted to look at these materials and incorporate organic groups into it. So that sounds like a great idea, but when you look at this material, you ask the question, how can I incorporate organic groups into this structure? You could swap out this inorganic A center here, so instead of, say, cesium plus, you could put an organic group, but that's a very small cavity, so you really just don't have that much space. So we want to create more space. We do this by layering the material. So we go from a 3D material to a 2D material, and this is still the perovskite structure. You can derive these layers by simply slicing through this 3D material, and now you just get more space to put more elaborate organic groups. So this has been the focus of the work in the group for our first year, and the hybrid perovskites or layered inorganic perovskites have been known since the 1970s, though more recently David Mitzi's group at IBM has done some really beautiful work studying the electronic properties of this dimensionally reduced inorganic sheets, and he has incorporated these materials as organic inorganic electronics, so he has built diodes and transistors with these. And David Mitzi's work has really, we've used this as a stepping stone for almost everything we've done in the group. So this is why we love these materials. These are well-defined materials. These are crystalline, and chemists love crystalline materials because we can grow single crystals of these materials, and we can use X-ray diffraction to know the precise atomic structure and connectivity of these solids. So it's a hybrid material where we have just perfect structural definition. It's also a really neat way to access dimensionally reduced inorganic structures within a bulk material, so you have heard of quantum dots and quantum wires. These materials have very unique electronic properties, but the way you access these properties is using very complicated processing techniques. When you have sheets or chains as a part of a bulk crystalline structure, the organic groups will isolate these sheets such that these materials will actually act like quantum confine inorganic structures, but these are much easier to synthesize. These structures are highly tunable. We can change this red sphere here, the metal 2+, we can change the hairline, we can change the connectivity of this inorganic sheet, we can change the thickness of the sheet, and of course we have all the vast structural and functional diversity of organic groups to put in as the R group here. And of course the idea is to make a material that shows properties of molecules and also shows properties of inorganic solids, but what I find even more fascinating is that the synergistic effects of having these molecular centers and inorganic solids can give rise to new properties in the hybrid that are not inherent to the parent components. These are synthesized in water or inorganic solvents at room temperature and pressure, these are extremely mild conditions compared to conditions of typical solid state synthesis. And we can deposit films of these materials on various substrates using solution state chemistry, so we can simply dip a wafer into a solution and coat that wafer with these materials. We can use drop casting, spin coating, and other extremely cheap techniques. And I wanted to highlight how we make these materials attempting to think about layer by layer deposition techniques when you see a layered material. This is not what we do, that's too hard. So we just throw everything into solution. So in solution, just in a beaker on the bench, we have all these precursors floating around and we ask these metal ions and these organic linkers to form this very ordered structure. So what I'm trying to show with this picture is that there are hundreds of other things that could form and we allow self-assembly to dictate the structure we want. So the challenge of self-assembly is that we need to sample a very large reaction space and find the correct conditions such that this whole bunch of this big mess here will actually form this beautiful ordered structure. But the beauty of self-assembly is that once you identify these conditions to make the layered structure, you can make the same structure each time you do it. So it's ideally reproducible and it's also a very nice way to get the same inorganic structure each time. So the thickness of the inorganic layers and the organic layers is dictated by the crystal structure. So it's just perfectly reproducible. There is no size distribution between synthesis. So today I will tell you about, I'll tell you two brief stories about studies that we very recently finished in the group as of yesterday. So this is very recent news. And I think this beautifully shows the strength of the hybrid platform. The first study I'll tell you about has what I like to call action at the organic layer and the second study will talk about action at the inorganic layer. So the first study was done by Dr. Diego Solicibara. He's a postdoctoral scholar in my group. And Diego found this really neat way to capture gases from air streams using a nonporous material. This is unusual because typically gas capture materials are porous. I mean, where would the substrates go? So these materials expand dramatically to incorporate substrates and we also found that we can release these substrates. And for the second part of my talk, I'll talk about Emma Donner's work. Emma is a junior at Stanford and she's worked in my group for two years now. And Emma found a way to stabilize this corrugated inorganic sheets instead of these flat sheets. And she found that these are very promising as white light emitters, so phosphors for solid state lighting devices. Very unusual for one single phase bulk material to emit white light, which corresponds to all the wavelengths in the visible spectrum. And I'll tell you about that towards the end. So when I started my group last year, I just asked my group to put anything that fits into the organic layer. I just wanted to see what we could form. So the goals were somewhat low initially. We just wanted to see if we could make this layer of materials. So in the process of making a more elaborate linker, Diego formed this alkyl chain with a terminal alkyne group. So chemists have a very nasty habit of not showing hydrogens. This might look a little odd, but there's simply a carbon-carbon triple bond that's hanging at the end of an alkyl chain. So we made this hybrid, well, Diego made this hybrid material with lead bromide sheets with dangling organic linkers between the sheets. And if you look at this material, it's completely non-porous. So here, so every picture I show you is a single crystal x-ray structure. So we can grow single crystals of these materials and these are the precise atomic positions of the materials. So if you look at the space-filling model, you see that the organic groups form a very densely packed layer and there is no space within this material. But if you open up a freshman organic chemistry book, I think somewhere in the first few chapters you find that alkyne groups, so carbon-carbon triple bonds, will react with halogens like chlorine, bromine, iodine and those halogens will add across the bonds. So because the solution state chemistry of triple bonds with iodine was known, we were just curious to see whether iodine could react with this solid state material. And I think we just did this because we could. But we exposed this crystalline solid to iodine vapor just in a beaker. It's a very simple experiment. We were really surprised to find that the entire material gets iodinated. So iodine vapor adds across this triple bond to form this double bond with two iodines. So it forms chemical bonds within this material. What's really remarkable about this transformation is that the crystallinity of the material remains. So initially you have this partially interdigitated organic layer that looks a bit like this and the whole material just swells only in one direction. And the swelling is huge. It's about 40% of the parent structure and it's really remarkable that this maintains the crystallinity. There's the largest reported unit cell expansion for a crystalline material. So this was neat and we, as chemists, we get excited over things like this. But I didn't actually think there was a use for this but we were pleased to find out after the fact that there's actually a need to capture iodine gas from air. So it turns out that nuclear power plants emit radioactive iodine as a final oxidation product of uranium and plutonium fuel. And initially these power plants will emit a whole bunch of different isotopes of iodine. So five to ten different isotopes of iodine and many of these have very short lifetimes. So if you let this nuclear fuel sit for about a week, you're left with just two isotopes. So I127 is the stable isotope and that's not a problem. But iodine 129 is a problem. So this is a gamma and beta emitter and has a half-life of 10 million years. And iodine is a gas. So we have a radioactive gas that lives for 10 million years. So there's a lot of interest in capturing this material. Iodine is especially nasty because it can very easily get into the food chain and get into waterways and any iodine that we consume ends up in a thyroid and there are strong correlations between this and thyroid cancers. So there's a lot of interest, especially in government labs, for creating a material that can capture iodine as a solid state product. The idea is to bury it somewhere safe for 10 million years. I'm not sure what's safe for 10 million years, but we certainly need to make iodine a non-volatile material through this capture material. There's also some developmental work on nuclear transmutation where you can capture all that iodine in a solid state material and zap it with radiation and convert it into a stable isotope, which sounds safer to me. So we looked at this material in terms of an iodine capture agent and it actually performs quite well. So if you look at the gravimetric capacity for iodine capture of this material, that is just how much iodine does it capture. So amount of iodine capture divided by amount of iodine plus weight of the capture material, we get a weight capacity of 43%. If we look at the highest reported numbers for iodine capture materials, we get 64% and 55% in metal-organic frameworks. But these frameworks are poorer structures. So it's quite impressive that a non-porous material has comparable weight capacities to porous materials. Now, for this specific purpose, we don't care so much about gravimetric capacity. You're not going to carry this iodine with you. So what really matters is volumetric capacity. And in terms of volumetric capacity, a non-porous structure will always win. So these materials have the highest volumetric capacities reported for iodine capture materials. And just to give you an idea of what's out there, right now most government labs at Sandia and Idaho are studying silver impregnated zeolites. So zeolites are porous metal oxide frameworks and these pores can be lined with silver nanoparticles. So the idea is that when iodine goes through, it just reacts with the silver form silver iodide, which is a solid. But we calculated the highest possible weight capacities of these materials and they have to be below 33%. So these numbers are better than the current technologies. So this looks great, but a question arises. Here the iodine capture occurs at the organic layer. So why make the hybrid? Why not use the organic molecule on its own? So we asked a question and we did a series of experiments where we assessed the activity of the organic molecule alone versus the hybrid perovskite. And we found that there are many reasons to make the hybrid material. So these organic groups on their own are extremely hygroscopic. It will just dissolve at ambient humidity and just form a puddle on your bench. And stability to moisture is important for capturing radioactive iodine because the waste streams are saturated with water. So your capture material cannot dissolve in the waste stream. And in contrast, the hybrid perovskite that we make with these groups can be stored on the benchtop for months and is stable at even very high relative humidity. In terms of thermal stability, all the hybrid materials we've made are at least 50 degrees more stable, sorry, stable two at least 50 degrees higher temperatures than the organic groups alone and these are all stable up to about 200 degrees Celsius, if not more. These waste streams also have more NOx gases than iodine. So NOx is NO and NO2. And the organic groups will typically react with NOx and it will simply get deactivated if you use the organic group alone. But what we found is that if you put these organic groups in the hybrid perovskite, it has far greater resistance to reactivity with NOx gases and selectively binds just iodine. We also found out there's something rather cool which is that lead shields are used as radiation shields. So we calculated if we did capture radioactive iodine in the organic groups, can the inorganic sheets actually shield that radiation? So we calculated the adsorption for both the gamma radiation and the beta radiation emitted from radioactive iodine and we found that using the hybrid material is far better than using the organic group which is not surprising because the lead bromide sheets have so much electron density. And the hybrid material will absorb that radiation a hundred times better than the organic group alone. So right now we think that we can use these materials to capture iodine in a very soft organic matrix and we can actually use the inorganic sheets to shield some of the radiation at least that is emitted from the iodine. And remember we formed covalent bonds so these are very strong linkages between iodine and carbon so that iodine is not going to come off. What we need to assess though is the binding enthalpies of these materials. The challenge with capturing radioactive iodine is that there's very low concentration of iodine in these waste streams. So we need either to increase the mixing efficiency of the gas and the solid such that the solid will constantly be able to capture this gas or we need to get a material with very high binding enthalpies and that this is planned for the future. So this was reactivity with triple bonds. We then moved to reactivity with double bonds. So the solution state reactions of a double bond carbon with iodine leads to iodine again addition across this double bond but this reaction now is reversible. So we were interested to see if the solid state material will also capture iodine reversibly. And we found that it does so this is an x-ray pattern that just shows that this material can get iodinated and it will lose that iodine. So you can see that the morphology of the crystals are actually maintained as iodine comes on and off so this material just breeds iodine in and out. So in solution the reaction of iodine with alkene groups will form the diidoalkane and this will live for about one hour. In the solid state we have this very large network of iodine-iodine interactions which we don't have in solution. So we can use this to stabilize the iodinated material and this allows us to form time-released capture materials. So using crystal engineering we were able to change the lifetime of this iodinated material from three hours all the way up to three days. And a time to release capture material is an interesting way to regenerate your capture material free of charge. So you can imagine using the capture material having that iodine flow come in and then engineering the material such that it holds the iodine for three days and during this time you can just transport it to your sequestration facility and just allow the iodine to be released and now you have regenerated your capture material. And it can also be used for sustained release of iodine. Iodine is a potent antiseptic and iodine is often used to disinfect the dust streams and for medical applications. So and the final thing we looked at is again you know pulling out organic chemistry books. We are in organic chemistry so we don't know much organic chemistry but these are very simple reactions. We know that the addition of bromine across double bonds is not reversible even though the addition of iodine is reversible. So indeed we found that if we add bromine to these materials we form the dibromo alkene and this is not reversible. So this is actually a nice way to remove small amounts of bromine from an iodine stream and this is important because iodine is an essential nutrient bromine is toxic to our bodies and everywhere you get iodine you get a small amount of bromine because it's very hard to separate iodine and bromine these have very similar chemical properties. So what we can do is use these materials which will reversibly bind iodine and irreversibly bind bromine to remove trace amounts of bromine from iodine streams which sounds useful. So that's activity at the organic layer now I want to change gears and tell you about Emma's work on synthesizing again hybrid perovskites that are white light emitters. And I'll give you a very brief background into why you would want to make phosphors for solid state lighting so as you all probably know the typical incandescent bulbs that we use the tungsten filament bulbs as well as fluorescent lamps are just inherently inefficient there's a lot of interest in moving to solid state lighting and this transition has been projected to reduce the electricity used for lighting by about half by the year 2025 so there's a lot of interest in developing these light emitting diodes and phosphors that are required for solid state lighting. So the way that white light is generated using solid state lighting devices is to use is to couple a light emitting diode and LED with some phosphors so the LED will excite the phosphor will emit some radiation and together this must appear white to our eye. So there are two ways currently explored to do this you could imagine a blue LED coated with a yellow phosphor and the idea is that some of the blue emission is allowed to penetrate through the LED such that the blue and the yellow will combine to appear white to our eye. And this gives a decent white light and it's no problem if you're just reading black text on a white sheet of paper this has very poor color rendition so a red does not look red to it using this light so you can imagine applications where color rendition is important if you're a surgeon doing an operation blood must appear red you must be able to distinguish internal organs so there are cases when this light will not do. Another strategy is to mix phosphors so you can imagine an ultraviolet LED hitting three different phosphors a red, green and blue phosphor this emission could look white. This also has problems because when you have three phosphors the emission of one phosphor might overlap with the excitation of another phosphor what this means is that the emitted light of one phosphor will just be reabsorbed by another phosphor instead of contributing to the white light and this causes inherent energy losses. It's also because you have three phosphors it's extremely unlikely that all three will degrade at the same rate so even though you start with a white light this light will get colored over time because it will decay faster than the others. So for these reasons there's a lot of interest in a single phase so one emitter which degrades at one rate broadband emitter so a single phase means one emitter and a broadband emitter that emits throughout the entire visible spectrum such that you also get good color rendition and there is a major target in solid state research. So Emma was studying directed self-assembly of hybrid perovskites she wanted to see what kinds of organic groups will template different connectivities of the inorganic sheets and what she found is that you could use two very similar organic groups and the difference between these two groups is just the length of this alkyl chain between the nitrogens and she found out that if she threw this into solution with lead bromide she made this material which has flat sheets and with lead bromide into solution she made this highly corrugated sheets so this was kind of neat that we could make two very different structures using very similar precursors and we just wanted to see what was different between these two materials so she looked at the optical properties of these materials and she measured the adsorption and the emission spectrum of this material and what she finds is something that's not surprising this is already documented in the literature this is an exotone binding energy this is characteristic of dimensionally reduced solids and then you get a band gap because this is a high band gap semiconductor if you look at the emission spectrum you get a very sharp emission band and this material appears blue so this is just a film of this material on a slide we irradiate it at about 400 nanometers and it emits blue and there are no surprises here but then she moved to the corrugated material and she did the same experiment and we were really surprised to find out that this glows white so the adsorption spectrum looks very similar again you get the exotone band and the band gap but the emission traverses the entire visible spectrum so from 400 to 700 nanometers so this is very unusual in a single material in a bulk material so she looked at the color produced by this white light and this is defined by the CIE coordinates shown here so what we found is that this material is pretty close to the emission of just sunlight and dune so if I focus on this inset in orange I show you the emission spectrum of the sun and we have just colored in yellow the visible region and this red line here shows the emission of MR's first generation material and if you look at this chromaticity diagram here we are right here in this shaded red box so there is a significant red component in this white light and that's actually exactly what you want this produces a warm white light which is perfect for internal illumination but she also found that you can tune the emission so she can change the amount of chloride and bromide she uses in this material and she can make a material that has the emission spectrum shown here in this black curve which basically gives you a cold white light so it's important that we can tune the emission because the transition of existing lighting to solid state lighting requires tuneability of the emission because there are certain applications where the specifications for the light have already been defined and must be met by the solid state replacements she also found that the color rendition is very high so because there is a broadband emission red looks red and doesn't look brown and the CRI values for our materials are above 80 and for any indoor application you want CRI values of above 80 it's actually quite close to this mixed phosphors but without the disadvantages of mixed phosphors we looked at the origin of the broadband emission and these are ongoing studies the lifetime of the emission across the entire range from 400 to 700 nanometers is about the same which tells us that a similar excited state emits to give this broad emission and Eric in material science for helping us take these lifetime measurements and we have a collaborator at the Max Planck Institute Bing Hai and he has done some very nice electronic structure calculations which have really guided our thinking here and we think that this is due to excited electrons that are trapped through elastic lattice deformations so as the material vibrates it traps the excited electrons which decays radiatively to give this broad emission so I want to I'm running out of time so I'm going to go a little quickly here but I just want to tell you where we stand with respect to the shortcomings of with respect to current technologies I mentioned previously that if you have a blue LED and a yellow phosphor you don't get great color rendition so if you look at this emission spectrum there's very little red in the spectrum so it's great for illuminating black and white but not very good for illuminating colors and also these materials are made at temperatures of about 1300 to 1900 degrees so very high temperature synthesis the emerging technologies involve using three different phosphors to generate white light and again I told you previously that this has problems with self-absorption and different degradation rates of the phosphors there are two new emerging technologies they both involve cadmium which is not great cadmium is toxic but it is interesting to note that quantum dots that are very very small so quantum dots in the 1 to 2 nanometers size scale emit white light and this is attributed to surface sites in these very small structures and this has very nice color rendition the problem is these materials these are tiny particles that have to be separated from each other if they aggregate the emission is quenched so along with developing these quantum dots you also have to develop some kind of dispersive polymer that is resistant to degradation with the UV light and of course no one really wants to work with cadmium in a large scale because of its toxicity so lead is not great in terms of toxicity either but cadmium is worse sure and this is also the next emerging technology is also based on cadmium so I just want to I'll just leave you with this this is a comparison of where we stand with respect to the current technologies and we think it's quite scalable though we do need to improve the quantum efficiencies I'm sorry I think I just lost the slide did we lose your students that was the most important part that was the most important part I should go back we can't lose the students that's important yeah I don't know how to get that back I would like to end with that slide she wants to get to the last slide if you just put out the last slide I'm done talking thank you so that's my group yeah and I just want to thank the following agencies for funding us perfect yes I'm really done talking thank you very much