Department of Chemistry
Permanent URI for this collectionhttps://hdl.handle.net/1807/16837
Established in 1859, the Department of Chemistry, with its advanced research facilities, is dedicated in conducting top notch research and providing excellent learning experiences for future great scientists. With 50 faculty members, 30 staffs, and over 200 graduate and post-doctoral students, the department has its focus on a wide range of research within chemistry (analytical, biological and organic, environmental, inorganic, physical, polymer and material, as well as chemical physics). However, advancement does not rely on single studies or research area, thus, the department also provides interdisciplinary research with the medical sciences and engineering faculties for an integrative approach.
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Item Degradable π-Conjugated Polymers(American Chemical Society, 2024-04) Uva, Azalea; Michailovich, Sofia; Hsu, Nathan Sung Yuan; Tran, HelenThe integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.Item Trans Ligand Determines the Stability of Paramagnetic Manganese(II) Hydrides of the Type trans-[MnH(L)(dmpe)2]+ Where L is PMe3, C2H4, or CO(ACS Publications, 2023-05) Rennie, Benjamin E; Price, Jeffrey S; Emslie, David J H; Morris, Robert HParamagnetic metal hydride (PMH) complexes play important roles in catalytic applications and bioinorganic chemistry. 3d PMH chemistry has largely focused on Ti, Mn, Fe, and Co. Various MnII PMHs have been proposed as intermediates in catalysis, but isolated MnII PMHs are limited to dimeric high-spin MnII structures with bridging hydrides. In this paper, a series of the first low-spin monomeric MnII PMH complexes are generated by chemical oxidation of their MnI analogues. This series is of the type trans-[MnH(L)(dmpe)2]+/0 where the trans ligand L is PMe3, C2H4, or CO [dmpe is 1,2-bis(dimethylphosphino)ethane], and the thermal stability of the MnII hydride complexes was found to be strongly dependent on the identity of the trans ligand. When L is PMe3, the complex is the first example of an isolated monomeric MnII hydride complex. In contrast, when L is C2H4 or CO, the complexes are only stable at low temperatures; upon warming to room temperature, the former decomposed to afford [Mn(dmpe)3]+, accompanied by ethane and ethylene, whereas the latter eliminated H2, generating [Mn(MeCN)(CO)(dmpe)2]+ or a mixture of products including [Mn(κ1-PF6)(CO)(dmpe)2], depending on the reaction conditions. All PMHs were characterized by low-temperature electron paramagnetic resonance (EPR) spectroscopy, and stable [MnH(PMe3)(dmpe)2]+ was further characterized by UV-vis and IR spectroscopy, Superconducting Quantum Interference Device magnetometry, and single-crystal X-ray diffraction. Noteworthy spectral properties are the significant EPR superhyperfine coupling to the hydride (∼85 MHz) and an increase (+33 cm-1) in the Mn-H IR stretch upon oxidation. Density functional theory calculations were also employed to gain insights into the acidity and bond strengths of the complexes. MnII-H bond dissociation free energies are estimated to decrease in the series of complexes from 60 (L = PMe3) to 47 kcal/mol (L = CO).Item 35+1 challenges in materials science being tackled by PIs under 35(ish) in 2023(Elsevier, 2023-08) Allen, Monica; Bediako, Kwabena; Bowman, William J.; Calabrese, Michelle; Caretta, Lucas; Cersonsky, Rose K.; Chen, Wen; Correa, Santiago; Davidson, Rachel; Dresselhaus-Marais, Leora; Eisler, Carissa N.; Furst, Ariel; Ge, Ting; Hook, Andrew; Hsu, Yi-Ting; Jia, Chunjing; Lu, Jianfeng; Lunghi, Alessandro; Messina, Marco S.; Moreno-Hernandez, Ivan A.; Nichols, Eva; Rao, Reshma; Seifrid, Martin; Shulenberger, Katherine Emily; Simonov, Alexandr N.; Su, Xiao; Swearer, Dayne F.; Tang, Evelyn; Taylor, Mercedes K.; Tran, Helen; Trindade, Gustavo F.; Truby, Ryan; Utzat, Hendrik; Yang, Ying; Yee, Daryl W.; Zhao, Shenlong; Cranford, SteveHere we highlight 35 (+1) global researchers approximately under the age of 35. The annual cohort was self-generated by initial seed invitations sent by the editorial team, with each contributor inviting the next in a self-selecting unrestricted (nominally supervised) manner. The final collection is an inspiring look at the challenges the current generation of materials researchers are tackling, demonstrating the interdisciplinarity of materials science.Item Biobased, Degradable, and Conjugated Poly(Azomethine)s(ACS Publications, 2023-02) Uva, Azalea; Lin, Angela; Tran, HelenCarotenoids are a class of biobased conjugated molecules that bear a resemblance to the substructure of polyacetylene, a well-known conductive but insoluble polymer. Solubility is an important physical attribute for processing materials using different techniques. To impart solubility in polymers, alkyl side chains are often included in the molecular design. While these design strategies are well explored in conjugated systems, they have not been implemented with carotenoids as a building block in polymers. Here, we show a series of carotenoid-based polymers with varying side chain lengths to tune solubility. Using carotenoid and p-phenylenediamine-based monomers, degradable and biobased poly(azomethine)s were synthesized via imine polycondensation. Maximum solubilities corresponding to the varying alkyl chain lengths were quantitatively determined by ultraviolet-visible (UV-vis) absorption spectroscopy. Since carotenoids are biobased with known degradation products, the effect of acidic and artificial sunlight-promoted degradation was systematically investigated using UV-vis spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, gel permeation chromatography (GPC), and high-resolution mass spectroscopy (HRMS). Our polymer system was found to have two modes of on-demand degradation, with acid hydrolysis accelerating the rate of polymer degradation and artificial sunlight generating additional degradation products. This work highlights carotenoid monomers as viable candidates in the design of biobased, degradable, and conjugated polymers.Item Conductive and elastic bottlebrush elastomers for ultrasoft electronics(Springer Nature, 2023-02) Xu, Pengfei; Wang, Shaojia; Lin, Angela; Min, Hyun-Kee; Zhou, Zhanfeng; Dou, Wenkun; Sun, Yu; Huang, Xi; Tran, Helen; Liu, XinyuUnderstanding biological systems and mimicking their functions require electronic tools that can interact with biological tissues with matched softness. These tools involve biointerfacing materials that should concurrently match the softness of biological tissue and exhibit suitable electrical conductivities for recording and reading bioelectronic signals. However, commonly employed intrinsically soft and stretchable materials usually contain solvents that limit stability for long-term use or possess low electronic conductivity. To date, an ultrasoft (i.e., Young's modulus <30 kPa), conductive, and solvent-free elastomer does not exist. Additionally, integrating such ultrasoft and conductive materials into electronic devices is poorly explored. This article reports a solvent-free, ultrasoft and conductive PDMS bottlebrush elastomer (BBE) composite with single-wall carbon nanotubes (SWCNTs) as conductive fillers. The conductive SWCNT/BBE with a filler concentration of 0.4 - 0.6 wt% reveals an ultralow Young's modulus (<11 kPa) and satisfactory conductivity (>2 S/m) as well as adhesion property. Furthermore, we fabricate ultrasoft electronics based on laser cutting and 3D printing of conductive and non-conductive BBEs and demonstrate their potential applications in wearable sensing, soft robotics, and electrophysiological recording.Item Thienoisoindigo-based recyclable conjugated polymers for organic electronics(Royal Society of Chemistry, 2023-12) Nozaki, Naoya; Uva, Azalea; Matsumoto, Hidetoshi; Tran, Helen; Ashizawa, MinoruImine-based semiconducting polymers based on thiophene-flanked diketopyrrolopyrrole (TDPP) are widely used to realize naturally disposable electronic devices. However, TDPP easily decomposes under mildly acidic conditions, limiting its potential for use in recyclable systems. Herein, we designed and synthesized two chemically recyclable thienoisoindigo (TII)-based polymers bearing an imine bond. These polymers were prepared from polycondensation reactions of the dialdehyde-functionalized monomer TII-(CHO)2 with p-phenylenediamine (PD) to produce p(TII-PD) and with 2,6-naphthalenediamine (2,6ND) to produce p(TII-2,6ND), respectively. Using ultraviolet-visible-near infrared spectroscopy, nuclear magnetic resonance, and mass spectroscopy, we examined the recyclability of both polymers. Under mildly acidic conditions, the imine-based polymers fully degrade into the original TII-(CHO)2 in as little as one day. Moreover, the recovered TII-(CHO)2 monomer is chemically stable for up to 6 months under acidic conditions, allowing us to isolate the monomer in high yield (>90%). Using the recovered TII-(CHO)2 monomer, we prepared recycled polymers, re-p(TII-PD) and re-p(TII-2,6ND). The recycled polymers displayed nearly the same electrical properties as the pristine polymers, with field-effect transistor mobilities in the order of 10−2–10−3 cm2 V−1 s−1. These results demonstrate the versatility of the TII-based monomer unit for developing fully recyclable semiconducting polymers.Item A Ruthenium Protic N-Heterocyclic Carbene Complex as a Precatalyst for the Efficient Transfer Hydrogenation of Aryl Ketone(American Chemical Society, 2022-07-22) Tsui, Brian T. H.; Sung, Molly M. H.; Kinas, Jenny; Hahn, F. Ekkehardt; Morris, Robert H.The neutral azole precursor to a protic NHC (pNHC) ligand, 6-((4,5-diphenyl-1H-imidazol-1-yl)methyl)-2,2’-bipyridine (3), was prepared from 6-(bromomethyl)-2,2’-bipyridine (2) and 4,5-diphenylimidazole. Complex [RuCl(pNHC-bpy)(PPh3)2](PF6) (4) bearing a protic, bipyridine-tethered NHC ligand was prepared by refluxing 3 with RuCl2(PPh3)3 and KPF6 in methanol and was characterized by NMR spectroscopy, mass spectrometry, elemental analysis and a single crystal X-ray diffraction study. The hydrido complex [RuH(pNHC-bpy)(PPh3)2](PF6) (5) was prepared by reaction of 4 with NaBH4 in ethanol and characterized by NMR and FTIR spectroscopy. Complex 5 was used as catalyst (0.1 mol% loading) in the transfer hydrogenation (TH) of a range of alkyl/aryl ketones in basic iso-propanol at 60 °C. Bulky alkyl groups or ortho-substituted aryl groups at the ketones slowed down or inhibited the catalytic transformation. The addition of an excess of triphenylphosphine also slowed the catalysis, providing an indication for a mechanism involving phosphine dissociation, while the addition of an excess of elemental mercury had only a small effect on the conversion. The importance of potassium cations in the mechanism is consistent with the observation of reduced catalytic conversion when [2,2,2]-cryptand was present or when 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was used as the base. A plausible homogenous catalysis mechanism involving the inner sphere addition of hydride to the substrate in the transition state TS1 is supported by DFT calculations where the potassium ion has replaced the hydrogen atom of the N–H group in the protic NHC.Item Designing materials acceleration platforms for heterogeneous CO2 photo(thermal)catalysis(Elsevier, 2023-05) Wang, Andrew; Bozal-Ginesta, Carlota; Hari Kumar, Sai Govind; Aspuru-Guzik, Alán; Ozin, Geoffrey A.Materials acceleration platforms (MAPs) combine automation and artificial intelligence to accelerate the discovery of molecules and materials. They have potential to play a role in addressing complex societal problems such as climate change. Solar chemicals and fuels generation via heterogeneous CO2 photo(thermal)catalysis is a relatively unexplored process that holds potential for contributing toward an environmentally and economically sustainable future and is therefore a very promising application for MAP science and engineering. Here, we present a brief overview of how design and innovation in heterogeneous CO2 photo(thermal)catalysis, from materials discovery to engineering and scaleup, could benefit from MAPs. We discuss relevant design and performance descriptors and the level of automation of state-of-the-art experimental techniques, and we review examples of artificial intelligence in data analysis. Based on these precedents, we finally propose a MAP outline for autonomous and accelerated discoveries in the emerging field of solar chemicals and fuels sourced from CO2 photo(thermal)catalysis.Item Electronic Insights into Aminoquinoline-Based PNHN Ligands: Protonation State Dictates Geometry While Coordination Environment Dictates N-H Acidity and Bond Strength(Royal Society of Chemistry, 2022-06-14) Gradiski, Matthew V.; Rennie, Benjamin E.; Lough, Alan J.; Morris, Robert H.A variety of transition metal complexes bearing aminoquinoline PNHH’-R ligands R = Ph (L1H), Cy (L2H) and their amido analogues are reported for rhodium(I) ([Rh(L1H)(PPh3)]+ 1 and Rh(L1)(PPh3) 2), cobalt(II) (Co(L1)(Cl) 4), and iron(II) ([Fe(L1H)2]2+ 5, Fe(L1)2 6, and [Fe(C5Me5)(L1H)]PF6 7). The acid-base and redox properties of the amido complexes 2, 6, and their protio parent complexes 1, and 5 permit the determination of the pKa and bond dissociation free energy (BDFE) of their N–H bonds while the ligand scaffold is coordinated to metal centres of square planar and octahedral geometry, respectively. From relative concentrations obtained by the use of 31P{1H} NMR spectroscopy, a pKaTHF value of 14 is calculated for rhodium complex 1, 6.4 for iron complex 5, and 24 for iron complex 7. These data, when combined with elecrochemical potentials obtained via cyclic voltammetry, allow the calculations of BDFE values for the N–H bond of 69 kcal/mol for 1, and of 55 kcal/mol for 5.Item Gas-Phase Fluorescence of Proflavine Reveals Two Close-Lying, Brightly Emitting States(2022-03-10) Djavani-Tabrizi, Iden; Jockusch, Rebecca ASurprising excitation-dependent, dual emission from a small organic model fluorophore is reported. Gas-phase fluorescence spectra of proflavine (a diaminoacridine) ions reveal two long-lived emitting states, with distinct bands separated by just 1700 cm-1. The relative intensities of these two bands depend on the excitation wavelength. Time-dependent density functional theory (TD-DFT) calculations support the existence of two close-lying singlet electronic states, with excitation into S2 predicted to be >1000-fold more likely than into S1. These data strongly suggest that internal conversion (IC) rates are suppressed relative to solvated proflavine, and that IC is competitive with intramolecular vibrational relaxation (IVR). This work offers an in-depth assessment of the gas-phase photophysics of a simple fluorophore that could open a new pathway to understanding dual emission in fluorophores.Item Electrochemistry of transition metal hydride diphosphine complexes trans-MH(X)(PP)2 and trans-[MH(L)(PP)2]+, M = Fe, Ru, Os; PP = chelating phosphine ligand(Elsevier, 2020-11-07) Drouin, Samantha D.; Maltby, Patricia A.; Rennie, Benjamin E.; Schweitzer, Caroline T.; Golombek, Adina; Cappellani, E. Paul; Morris, Robert H.A series of over 30 iron, ruthenium, and osmium hydride phosphine complexes are reported, along with their MIII/II redox potentials. The complexes are of the type MH(PP)n(X) or [MH(PP)n(L)]+, where PP is one of the following bidentate phosphine ligands: dppe, dtpe, depe, and dtfpe, with n =2; or the tetradentate phosphine ligand meso-tet-1, with n = 1. The electrochemical data of these complexes and those from the literature are used to determine the Lever EL parameter of -0.65 V for the hydride ligand for iron and ruthenium. For osmium, however, the EL value for the hydride ligand is found to be more positive at only -0.37 V, an increase which is attributed to Os-H bond strengthening due to relativistic effects. The correlation holds for irreversible oxidations as well as reversible ones. These EL values can now be used along with Lever’s equations to predict redox potentials of other iron-group hydride complexes.Item Bioderived and degradable polymers for transient electronics(2021-05) Uva, Azalea; Lin, Angela; Babi, Jon; Tran, HelenAs single-use electronics become more prevalent in our society, a shift towards devices with alternative disposal fates will be required to address rising levels of electronic and plastic waste. Adopting transient electronics is one solution for inadvertent litter of future single-use electronics as they are designed to automatically break down in environmental conditions after their intended use. However, the selection of appropriate source materials to make these transient devices is vital to ensure environmental compatibility. This mini-review aims to highlight recent advancements in bioderived polymers that can be used as substrates or encapsulants, the largest weight percentage in a device, in transient electronics. The chemical and biological degradation of these bioderived polymers is also discussed to present potential non-toxic byproducts and factors affecting degradation rates. Lastly, the potential outlook of transient electronics in biomedical, environmental, and consumer applications are proposed to demonstrate the wide scope of opportunities to be explored. © 2021 Society of Chemical Industry (SCI).Item Molecular protectors: Superheroes for nanostructures(2021-08) Babi, Jon; Uva, Azalea; Clapperton, Abigail Mae; Lin, Angela; Tran, HelenProtecting complex nanostructures from degradation in physiological fluids while preserving their function remains a major limitation toward their implementation in biosensing and drug delivery. Using peptoid oligomers, Gang and coworkers protect DNA origami structures from Mg2+ depletion and enzymatic breakdown.Item Self-Assembled Free-Floating Nanomaterials from Sequence Defined Polymers(2021-07) Babi, Jon; Zhu, Linglan; Lin, Angela; Uva, Azalea; El‐Haddad, Hana; Peloewetse, Atang; Tran, HelenSequence-defined polymers can be programmed to self-assemble into precise nanostructures for applications in biosensing, drug delivery, optics, and molecular computation. Inspired by the natural self-assembly processes present in biological protein and DNA systems, sets of molecular design rules have emerged across materials classes as instructions to build a variety of tunable structures. This review highlights recent advances in self-assembled sequence-defined and sequence-specific polymers across peptides, peptoids, DNA, and non-biological synthetic materials, with a focus on synthesis, assembly processes and overall structure. Specifically, these self-assembled structures are free-floating, as such constructs can potentially serve as a platform for the aforementioned applications. Emphasis is placed on the molecular design of polymers that self-assemble into zero-dimensional, one-dimensional, two-dimensional, or three-dimensional nanostructures. With the development of automated syntheses and increasing control over self-assembly, future work may focus on emerging classes of compatible hybrid materials with exciting directions toward new architectures and applications.Item Materials design for resilience in the biointegration of electronics(2021) Lin, Angela; Uva, Azalea; Babi, Jon; Tran, HelenDesigning biointegrated electronics for resilience starts at the molecular level, whereby “molecular architecture” dictates function. The ability to predict how variations in molecular level features translate to bulk polymer properties is critical for realizing large-scale bulk applications and opening avenues for niche applications. Inspired by architectural resilient design principles, this article reviews analogous principles for materials used in biointegrated electronics, including strategies to address mechanical mismatch, fouling, improper adhesion, and degradation within biological systems. Moreover, innovations in artificial intelligence and automation that will play an important role in elucidating new material design principles and their practical large-scale construction are discussed. Finally, alternative avenues for simplifying the production of future biointegrated electronics are proposed, such as using self-assembly processes that draw inspiration from biology to construct devices in vivo.Item A Field Guide to Optimizing Peptoid Synthesis(2022-09) Clapperton, Abigail Mae; Babi, Jon; Tran, HelenN-Substituted glycines (peptoids) are a class of peptidomimetic molecules used as materials for health, environmental, and drug delivery applications. Automated solid-phase synthesis is the most widely used approach for preparing polypeptoids, with a range of published protocols and modifications for selected synthetic targets. Simultaneously, emerging solution-phase syntheses are being leveraged to overcome limitations in solid-phase synthesis and access high-molecular weight polypeptoids. This Perspective aims to outline strategies for the optimization of both solid- and solution-phase synthesis, provide technical considerations for robotic synthesizers, and offer an outlook on advances in synthetic methodologies. The solid-phase synthesis sections explore steps for protocol optimization, accessing complex side chains, and adaptation to robotic synthesizers; the sections on solution-phase synthesis cover the selection of initiators, side chain compatibility, and strategies for controlling polymerization efficiency and scale. This text acts as a “field guide” for researchers aiming to leverage the flexibility and adaptability of peptoids in their research.Item Anisotropic, Nonthermal Lattice Disordering Observed in Photoexcited PbS Quantum Dots(2021-09) Krawczyk, Kamil M.; Sarracini, Antoine; Green, Philippe B.; Hasham, Minhal; Tang, Kuangyi; Paré-Labrosse, Olivier; Voznyy, Oleksandr; Wilson, Mark W. B.; Miller, R. J. DwayneGiven their nanoscale dimensions, colloidal semiconductor nanocrystals provide unique systems for investigating the dynamics controlling surface chemistry and fundamental issues regarding lattice reorganization upon changes in electron distribution. These systems are particularly amenable to ultrafast electron probes, offering an atomic level picture of the lattice reorganization involved following photoexcitation. Here, we study lead sulfide (PbS) quantum dots with ultrafast electron diffraction to characterize the atomic motions following high-intensity photoexcitation. Short-range nonthermal lattice distortions and increased atomic disorder were observed in PbS colloidal quantum dots ranging from 2.4 to 8.7 nm in size. These effects scaled inversely with size and were less pronounced in nanocrystals with a chloride-containing surface rather than only organic ligands, which is consistent with an effect arising at the surface. The anisotropic, nonthermal lattice disordering occurs preferentially along the (100) crystallographic directions, which could indicate an anisotropic distribution of localized charge between the differing lattice terminations of the {111} and {100} crystal facets. This is consistent with the larger anharmonicity for the lattice potential at lattice sites with reduced ligand coordination relative to the bulk, which has been shown to cause accelerated relaxation into dynamic and static surface trap sites. Through an exploration of quantum dot size and variation in surface termination, this work provides the missing structural details to advance our understanding and control of charge-carrier formation, trapping, and recombination processes in nanoscale semiconductor systems.Item Sub-Bandgap Optical Modulation of Quantum Dot Blinking Statistics(2020-08-06) Hasham, Minhal; Wilson, Mark W BColloidal quantum dots (QDs) suffer from pervasive photoluminescence intermittency that frustrates applications and correlates with irreversible photodegradation. In single-QD spectroscopies, blinking manifests as sporadic switching between ON and OFF states without a characteristic time scale, and the longstanding search for mechanisms has been recently accelerated by techniques to controllably modulate the QD environment. Here, we develop an all-optical modulation scheme and demonstrate that sub-bandgap light tuned to the stimulated emission transition perturbs the blinking statistics of individual CdSe/ZnS core/shell QDs. Resonant optical modulation progressively suppresses long-duration ON events, quantified by a power-law slope that is more negative on average (ΔαON = 0.46 ± 0.09), while OFF distributions and truncation times are unaffected. This characteristic effect is robust to choices in background subtraction and statistical analysis but supports mechanistic descriptions beyond first-order kinetics. This demonstration of all-optical perturbation of QD blinking dynamics provides an experimental avenue to disentangle the complex photophysics of photoluminescence intermittency.Item Binary Cu2-xS Templates Direct the Formation of Quaternary Cu2ZnSnS4 (Kesterite, Wurtzite) Nanocrystals(2021-10-27) Yarur Villanueva, Francisco; Green, Philippe B; Qiu, Chenyue; Ullah, Shahnaj R; Buenviaje, Kirstin; Howe, Jane Y; Majewski, Marek B; Wilson, Mark W BKesterite Cu2ZnSnS4 (k-CZTS) nanocrystals have received attention for their tunable optoelectronic properties, as well as the earth abundance of their constituent atoms. However, the phase-pure synthesis of these quaternary NCs is challenging due to their polymorphism, as well as the undesired formation of related binary and ternary impurities. A general synthetic route to tackle this complexity is to pass through intermediate template nanocrystals that direct subsequent cation exchange toward the desired quaternary crystalline phase, particularly those that are thermodynamically disfavored or otherwise synthetically challenging. Here, working within this model multinary system, we achieve control over the formation of three binary copper sulfide polymorphs, cubic digenite (Cu1.8S), hexagonal covellite (CuS), and monoclinic djurleite (Cu1.94S). Controlled experiments with Cu0 seeds show that selected binary phases can be favored by the identity and stoichiometry of the sulfur precursor alone under otherwise comparable reaction conditions. We then demonstrate that the nature of the Cu2-xS template dictates the final polymorph of the CZTS nanocrystal products. Through digenite, the cation exchange reaction readily yields the k-CZTS phase due to its highly similar anion sublattice. Covellite nanocrystals template the k-CZTS phase but via major structural rearrangement to digenite that requires elevated temperatures in the absence of a strong reducing agent. In contrast, we show that independently synthesized djurleite nanorods template the formation of the wurtzite polymorph (w-CZTS) but with prominent stacking faults in the final product. Applying this refined understanding to the standard one-pot syntheses of k- and w-CZTS nanocrystals, we identify that these reactions are each effectively templated by binary intermediates formed in situ, harnessing their properties to guide the overall synthesis of phase-pure quaternary materials. Our results provide tools for the careful development of tailored nanocrystal syntheses in complex polymorphic systems.Item Glycol ether additives control the size of PbS nanocrystals at reaction completion(2020) Green, Philippe B.; Wang, Zhibo; Sohn, Philip; Imperiale, Christian J.; Voznyy, Oleksandr; Wilson, Mark W. B.Improving chemical control over the nucleation and growth of colloidal nanocrystals advances optoelectronic applications. Here, we find that added glycol ethers promote the nucleation of PbS nanocrystals over the formation of metastable clusters, offering orthogonal control of nanocrystal size at reaction completion. This effect correlates with multidentate co-ordination to Pb(oleate)2.