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Rakshit S, Cohen B, Gutiérrez M, El-Ballouli AO, Douhal A. Deep Blue and Highly Emissive ZnS-Passivated InP QDs: Facile Synthesis, Characterization, and Deciphering of Their Ultrafast-to-Slow Photodynamics. ACS APPLIED MATERIALS & INTERFACES 2023; 15:3099-3111. [PMID: 36608171 PMCID: PMC10089568 DOI: 10.1021/acsami.2c16289] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2022] [Accepted: 12/19/2022] [Indexed: 05/30/2023]
Abstract
InP-based quantum dots (QDs) are an environment-friendly alternative to their heavy metal-ion-based counterparts. Herein we report a simple procedure for synthesizing blue emissive InP QDs using oleic acid and oleylamine as surface ligands, yielding ultrasmall QDs with average sizes of 1.74 and 1.81 nm, respectively. Consecutive thin coating with ZnS increased the size of these QDs to 4.11 and 4.15 nm, respectively, alongside a significant enhancement of their emission intensities centered at ∼410 nm and ∼430 nm, respectively. Pure phase synthesis of these deep-blue emissive QDs is confirmed by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Armed with femtosecond to millisecond time-resolved spectroscopic techniques, we decipher the energy pathways, reflecting the effect of successive ZnS passivation on the charge carrier (electrons and holes) dynamics in the deep-blue emissive InP, InP/ZnS, and InP/ZnS/ZnS QDs. Successive coating of the InP QDs increases the intraband relaxation times from 200 to 700 fs and the lifetime of the hot electrons from 2 to 8 ps. The lifetime of the cold holes also increase from 1 to 4 ps, and remarkably, the Auger recombination escalates from 15 to 165 ps. The coating also drastically decreases the quenching by the molecular oxygen of the trapped charge carriers at the surfaces of the QDs. Our results provide clues to push further the emission of InP QDs into more energetically spectral regions and to increase the fluorescence quantum yield, targeting the construction of efficient UV-emissive light-emitting devices (LEDs).
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2
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Singh B, Sikarwar S, Agarwal S, Singh DP, Pandey KK, Manohar R. Chemically Functionalized Gold Nanosphere-Blended Nematic Liquid Crystals for Photonic Applications. ACS OMEGA 2023; 8:2315-2327. [PMID: 36687113 PMCID: PMC9850737 DOI: 10.1021/acsomega.2c06718] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 12/19/2022] [Indexed: 06/17/2023]
Abstract
A demand for functional materials that are capable of tailoring light-emissive properties has apparently been rising nowadays substantially for their utilization in organic optoelectronic devices. Motivated by such promising characteristics, we present highly emissive as well as aggregation-induced emission (AIE) electroluminescent composite systems composed of a nematic liquid crystals (NLC) blended with polyethylene-functionalized gold nanospheres (GNSs). The major findings of this study include superior electro-optical properties such as threshold voltage reduction by around 24%. The fall time is reduced by 11.50, 30.33, 49.33, and 63.17% respectively, and rotational viscosity is reduced by 13.86, 32.77, 36.97, and 49.58% for 5.0 × 1011, 5.0 × 1012, 2.5 × 1013, and 5.0 × 1013 number of GNS-blended liquid crystal (LC) cells. The increased UV absorbance and greatly enhanced luminescence properties have been attributed to surface plasmon resonance near the surface of GNSs and AIE effect risen due to agglomeration of the capping agent with the NLC molecules respectively, and these characteristics make them suitable for new-age display applications.
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Affiliation(s)
- Bhupendra
Pratap Singh
- Liquid
Crystal Research Laboratory, Department of Physics, University of Lucknow, Lucknow226007, India
| | - Samiksha Sikarwar
- Integrated
Basic Science, School of Physical and Decision Science, Babasaheb Bhimrao Ambedkar University, Lucknow226025, India
| | - Shikha Agarwal
- Liquid
Crystal Research Laboratory, Department of Physics, University of Lucknow, Lucknow226007, India
| | - Dharmendra Pratap Singh
- Université
du Littoral Côte d’Opale, UR 4476, UDSMM, Unité de Dynamique et Structure des Matériaux
Moléculaires, Calais62228, France
| | - Kamal Kumar Pandey
- Department
of Physics, Shri Jai Narain Misra Post Graduate
College, Lucknow226001, India
| | - Rajiv Manohar
- Liquid
Crystal Research Laboratory, Department of Physics, University of Lucknow, Lucknow226007, India
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3
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Westmoreland DE, López-Arteaga R, Kantt LP, Wasielewski MR, Weiss EA. Dynamic Tuning of the Bandgap of CdSe Quantum Dots through Redox-Active Exciton-Delocalizing N-Heterocyclic Carbene Ligands. J Am Chem Soc 2022; 144:4300-4304. [DOI: 10.1021/jacs.1c12842] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Dana E. Westmoreland
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Rafael López-Arteaga
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Leanna Page Kantt
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Michael R. Wasielewski
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Emily A. Weiss
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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4
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Park N, Eagle FW, DeLarme AJ, Monahan M, LoCurto T, Beck R, Li X, Cossairt BM. Tuning the interfacial stoichiometry of InP core and InP/ZnSe core/shell quantum dots. J Chem Phys 2021; 155:084701. [PMID: 34470352 DOI: 10.1063/5.0060462] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
We demonstrate fine-tuning of the atomic composition of InP/ZnSe quantum dots (QDs) at the core/shell interface. Specifically, we control the stoichiometry of both anions (P, As, S, and Se) and cations (In and Zn) at the InP/ZnSe core/shell interface and correlate these changes with the resultant steady-state and time-resolved optical properties of the nanocrystals. The use of reactive trimethylsilyl reagents results in surface-limited reactions that shift the nanocrystal stoichiometry to anion-rich and improve epitaxial growth of the shell layer. In general, anion deposition on the InP QD surface results in a redshift in the absorption, quenching of the excitonic photoluminescence, and a relative increase in the intensity of broad trap-based photoluminescence, consistent with delocalization of the exciton wavefunction and relaxation of exciton confinement. Time-resolved photoluminescence data for the resulting InP/ZnSe QDs show an overall small change in the decay dynamics on the ns timescale, suggesting that the relatively low photoluminescence quantum yields may be attributed to the creation of new thermally activated charge trap states and likely a dark population that is inseparable from the emissive QDs. Cluster-model density functional theory calculations show that the presence of core/shell interface anions gives rise to electronic defects contributing to the redshift in the absorption. These results highlight a general strategy to atomistically tune the interfacial stoichiometry of InP QDs using surface-limited reaction chemistry allowing for precise correlations with the electronic structure and photophysical properties.
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Affiliation(s)
- Nayon Park
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Forrest W Eagle
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Asher J DeLarme
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Madison Monahan
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Talia LoCurto
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Ryan Beck
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Xiaosong Li
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
| | - Brandi M Cossairt
- Department of Chemistry, University of Washington, Seattle, Washington, 98195-1700, USA
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Martinet Q, Baronnier J, Girard A, Albaret T, Saviot L, Mermet A, Abecassis B, Margueritat J, Mahler B. Ligand-dependent nano-mechanical properties of CdSe nanoplatelets: calibrating nanobalances for ligand affinity monitoring. NANOSCALE 2021; 13:8639-8647. [PMID: 33942037 DOI: 10.1039/d1nr00270h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The influence of ligands on the low frequency vibration of cadmium selenide colloidal nanoplatelets of different thicknesses is investigated using resonant low frequency Raman scattering. The strong vibration frequency shifts induced by ligand modifications as well as sharp spectral linewidths make low frequency Raman scattering a tool of choice to follow ligand exchange as well as the nano-mechanical properties of the NPLs, as evidenced by a carboxylate to thiolate exchange study. Apart from their molecular weight, the nature of the ligands, such as the sulfur to metal bond of thiols, induces a modification of the NPLs as a whole, increasing the thickness by one monolayer. Moreover, as the weight of the ligands increases, the discrepancy between the mass-load model and the experimental measurements increase. These effects are all the more important when the number of layers is small and can only be explained by a modification of the longitudinal sound velocity. This modification takes its origin in a change of the lattice structure of the NPLs, that reflects on their elastic properties. These nanobalances are finally used to characterize ligand affinity with the surface using binary thiol mixtures, illustrating the potential of low frequency Raman scattering to finely characterize nanocrystal surfaces.
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Affiliation(s)
- Quentin Martinet
- Institut Lumière Matière Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306, F-69622 Villeurbanne, France.
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6
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Weiss EA. Influence of Shape Anisotropy on the Emission of Low-Dimensional Semiconductors. ACS NANO 2021; 15:3568-3577. [PMID: 33691063 DOI: 10.1021/acsnano.1c01337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The emergence of precise and scalable synthetic methods for producing anisotropic semiconductor nanostructures provides opportunities to tune the photophysical properties of these particles beyond their band gaps, and to incorporate them into higher-order structures with macroscopic anisotropic responses to electric and optical fields. This perspective article discusses some of these opportunities in the context of colloidal semiconductor nanoplatelets, with a focus on the influence of confinement anisotropy on processes that dictate the emission.
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Affiliation(s)
- Emily A Weiss
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
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Hottechamps J, Noblet T, Erard M, Dreesen L. Quenched or alive quantum dots: The leading roles of ligand adsorption and photoinduced protonation. J Colloid Interface Sci 2021; 594:245-253. [PMID: 33765644 DOI: 10.1016/j.jcis.2021.02.116] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 02/23/2021] [Accepted: 02/25/2021] [Indexed: 10/22/2022]
Abstract
HYPOTHESIS The fluorescence emission of water-soluble CdTe quantum dots (QDs) capped with mercaptocarboxylic acids (MCAs) is known to be pH-dependent. However, this behaviour is quite different from a study to another, so that literature suffers from a lack of coherence. Here we assume that the QD fluorescence efficiency is actually driven by the acid-base equilibrium of MCA thiol groups, and that light-excited QDs open a non-radiative relaxation path through photoinduced protonation. EXPERIMENTS We address this issue by examining colloidal CdTe QDs with (time-resolved) fluorescence spectroscopy under various conditions of acidity and light excitation. FINDINGS It appears that the emission of QDs is quenched below a critical pH value of 6.87, and that light excitation power strengthens this quenching. We thus demonstrate the existence of an additional photochemical process and developed a mathematical modeling accounting for all our experimental results. With only three parameters, it is possible to accurately predict the fluorescence decay of QDs over time, at any pH. Further, we also related the critical pH value of 6.87 to QD surface properties, explaining why observations may differ from a study to another and making the literature much more coherent.
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Affiliation(s)
- Julie Hottechamps
- GRASP-Biophotonics, CESAM, University of Liege, Institute of Physics, Allée du 6 août 17, 4000 Liège, Belgium
| | - Thomas Noblet
- GRASP-Biophotonics, CESAM, University of Liege, Institute of Physics, Allée du 6 août 17, 4000 Liège, Belgium
| | - Marie Erard
- Université Paris-Saclay, CNRS, Institut de Chimie Physique, UMR 8000, 91405 Orsay, France
| | - Laurent Dreesen
- GRASP-Biophotonics, CESAM, University of Liege, Institute of Physics, Allée du 6 août 17, 4000 Liège, Belgium.
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8
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Spatial Dependence of the Dipolar Interaction between Quantum Dots and Organic Molecules Probed by Two-Color Sum-Frequency Generation Spectroscopy. Symmetry (Basel) 2021. [DOI: 10.3390/sym13020294] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Given the tunability of their optical properties over the UV–Visible–Near IR spectral range, ligand-capped quantum dots (QDs) are employed for the design of optical biosensors with low detection threshold. Thanks to non-linear optical spectroscopies, the absorption properties of QDs are indeed used to selectively enhance the local vibrational response of molecules located in their vicinity. Previous studies led to assume the existence of a vibroelectronic QD–molecule coupling based on dipolar interaction. However, no systematic study on the strength of this coupling has been performed to date. In order to address this issue, we use non-linear optical Two-Color Sum-Frequency Generation (2C-SFG) spectroscopy to probe thick QD layers deposited on calcium fluoride (CaF2) prisms previously functionalized by a self-assembled monolayer of phenyltriethoxysilane (PhTES) molecules. Here, 2C-SFG is performed in Attenuated Total Reflection (ATR) configuration. By comparing the molecular vibrational enhancement measured for QD–ligand coupling and QD–PhTES coupling, we show that the spatial dependence of the QD–molecule interactions (∼1/r3, with r the QD–molecule distance) is in agreement with the hypothesis of a dipole–dipole interaction.
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9
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Delmas WG, Vickers ET, DiBenedetto AC, Lum C, Hernandez IN, Zhang JZ, Ghosh S. Modulating Charge Carrier Dynamics and Transfer via Surface Modifications in Organometallic Halide Perovskite Quantum Dots. J Phys Chem Lett 2020; 11:7886-7892. [PMID: 32870009 DOI: 10.1021/acs.jpclett.0c02151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We investigate the effect of functionalization by acid/amine combinations of four aromatic capping ligands on the optoelectronic properties of CH3NH3PbBr3 perovskite quantum dots (PQDs). These include benzoic acid (BA), phenylacetic acid (PAA), benzylamine, and isopropyl benzylamine. We observe that charge transfer efficiency in PQD films comprising BA-ligated samples varies between 12% and 95% as the dot density is tuned from 102 to 105 dots/μm2 but is consistently ∼92% over that entire range for PAA-ligated PQDs. As temperature T decreases, initially, recombination is dominated by bound or trapped excitons, but below 80 K, spectral broadening, accompanied by free excitonic behavior, is observed. Our results indicate enhanced charge delocalization at lower values of T, which reduces the level of exciton confinement and recombination decay rates and underlines the importance of investigating PQD-ligand interactions at a fundamental level given the significant effect minute changes in ligand structures have on the optoelectronic properties of quantum dots.
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Affiliation(s)
- William G Delmas
- Department of Physics, School of Natural Sciences, University of California, Merced, California 95344, United States
| | - Evan T Vickers
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States
| | - Albert C DiBenedetto
- Department of Physics, School of Natural Sciences, University of California, Merced, California 95344, United States
| | - Calista Lum
- Department of Physics, School of Natural Sciences, University of California, Merced, California 95344, United States
| | - Isaak N Hernandez
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Jin Z Zhang
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States
| | - Sayantani Ghosh
- Department of Physics, School of Natural Sciences, University of California, Merced, California 95344, United States
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10
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Westmoreland DE, López-Arteaga R, Weiss EA. N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots. J Am Chem Soc 2020; 142:2690-2696. [PMID: 31934758 DOI: 10.1021/jacs.9b13605] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Delocalization of excitons within semiconductor quantum dots (QDs) into states at the interface of the inorganic core and organic ligand shell by so-called "exciton-delocalizing ligands (EDLs)" is a promising strategy to enhance coupling of QD excitons with proximate molecules, ions, or other QDs. EDLs thereby enable enhanced rates of charge carrier extraction from, and transport among, QDs and dynamic colorimetric sensing. The application of reported EDLs-which bind to the QDs through thiolates or dithiocarbamates-is however limited by the irreversibility of their binding and their low oxidation potentials, which lead to a high yield of photoluminescence-quenching hole trapping on the EDL. This article describes a new class of EDLs for QDs, 1,3-dimethyl-4,5-disubstituted imidazolylidene N-heterocyclic carbenes (NHCs), where the 4,5-substituents are Me, H, or Cl. Postsynthetic ligand exchange of native oleate capping ligands for NHCs results in a bathochromic shift of the optical band gap of CdSe QDs (R = 1.17 nm) of up to 111 meV while the colloidal stability of the QDs is maintained. This shift is reversible for the MeNHC-capped and HNHC-capped QDs upon protonation of the NHC. The magnitude of exciton delocalization induced by the NHC (after scaling for surface coverage) increases with the increasing acidity of its π system, which depends on the substituent in the 4,5-positions of the imidazolylidene. The NHC-capped QDs maintain photoluminescence quantum yields of up to 4.2 ± 1.8% for shifts of the optical band gap as large as 106 meV.
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Affiliation(s)
- Dana E Westmoreland
- Department of Chemistry , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208-3113 , United States
| | - Rafael López-Arteaga
- Department of Chemistry , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208-3113 , United States
| | - Emily A Weiss
- Department of Chemistry , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208-3113 , United States
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11
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Azzaro MS, Le AK, Wang H, Roberts ST. Ligand-Enhanced Energy Transport in Nanocrystal Solids Viewed with Two-Dimensional Electronic Spectroscopy. J Phys Chem Lett 2019; 10:5602-5608. [PMID: 31475832 DOI: 10.1021/acs.jpclett.9b02040] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We examine CdSe NCs functionalized with the exciton-delocalizing ligand phenyldithiocarbamate (PDTC) using two-dimensional electronic spectroscopy (2DES). PDTC forms hybrid molecular orbitals with CdSe's valence band that relax hole spatial confinement and create potential for enhanced exciton migration in NC solids. We find PDTC broadens the intrinsic line width of individual NCs in solution by ∼30 meV, which we ascribe to modulation of NC band edge states by ligand motion. In PDTC-exchanged solids, photoexcited excitons are mobile and rapidly move to low-energy NC sites over ∼30 ps. We also find placing excitons into high-energy states can accelerate their rate of migration by over an order of magnitude, which we attribute to enhanced spatial delocalization of these states that improves inter-NC wave function overlap. Our work demonstrates that NC surface ligands can actively facilitate inter-NC energy transfer and highlights principles to consider when designing ligands for this application.
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Affiliation(s)
- Michael S Azzaro
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Aaron K Le
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Honghao Wang
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Sean T Roberts
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
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12
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Liyanage T, Masterson AN, Oyem HH, Kaimakliotis H, Nguyen H, Sardar R. Plasmoelectronic-Based Ultrasensitive Assay of Tumor Suppressor microRNAs Directly in Patient Plasma: Design of Highly Specific Early Cancer Diagnostic Technology. Anal Chem 2019; 91:1894-1903. [DOI: 10.1021/acs.analchem.8b03768] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Thakshila Liyanage
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Adrianna N. Masterson
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Hector H. Oyem
- School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
| | - Hristos Kaimakliotis
- Department of Urology, Indiana University School of Medicine, 535 N. Barnhill Dr., Indianapolis, Indiana 46202, United States
| | - Hang Nguyen
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Rajesh Sardar
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
- Integrated Nanosystems Development Institute, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
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14
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Azzaro MS, Dodin A, Zhang DY, Willard AP, Roberts ST. Exciton-Delocalizing Ligands Can Speed Up Energy Migration in Nanocrystal Solids. NANO LETTERS 2018; 18:3259-3270. [PMID: 29652509 DOI: 10.1021/acs.nanolett.8b01079] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Researchers have long sought to use surface ligands to enhance energy migration in nanocrystal solids by decreasing the physical separation between nanocrystals and strengthening their electronic coupling. Exciton-delocalizing ligands, which possess frontier molecular orbitals that strongly mix with nanocrystal band-edge states, are well-suited for this role because they can facilitate carrier-wave function extension beyond the nanocrystal core, reducing barriers for energy transfer. This report details the use of the exciton-delocalizing ligand phenyldithiocarbamate (PDTC) to tune the transport rate and diffusion length of excitons in CdSe nanocrystal solids. A film composed of oleate-terminated CdSe nanocrystals is subjected to a solid-state ligand exchange to replace oleate with PDTC. Exciton migration in the films is subsequently investigated by femtosecond transient absorption. Our experiments indicate that the treatment of nanocrystal films with PDTC leads to rapid (∼400 fs) downhill energy migration (∼80 meV), while no such migration occurs in oleate-capped films. Kinetic Monte Carlo simulations allow us to extract both rates and length scales for exciton diffusion in PDTC-treated films. These simulations reproduce dynamics observed in transient absorption measurements over a range of temperatures and confirm excitons hop via a Miller-Abrahams mechanism. Importantly, our experiments and simulations show PDTC treatment increases the exciton hopping rate to 200 fs, an improvement of 5 orders of magnitude relative to oleate-capped films. This exciton hopping rate stands as one of the fastest determined for CdSe solids. The facile, room-temperature processing and improved transport properties offered by the solid-state exchange of exciton-delocalizing ligands show they offer promise for the construction of strongly coupled nanocrystal arrays.
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Affiliation(s)
| | - Amro Dodin
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | | | - Adam P Willard
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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15
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Ding WL, Peng XL, Sun ZZ, Li ZS. The electron injection rate in CdSe quantum dot sensitized solar cells: from a bifunctional linker and zinc oxide morphology. NANOSCALE 2017; 9:16806-16816. [PMID: 29072766 DOI: 10.1039/c7nr04847e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Herein, we have investigated the effect of both the bifunctional linker (L1, L2, L3, and L4) and ZnO morphology (porous nanoparticles (NPs), nanowires (NWs), and nanotubes (NTs-A and NTs-Z)) on the electron injection in CdSe QD sensitized solar cells by first-principles simulation. Via calculating the partitioned interfaces formed by different components (linker/QDs and ZnO/linker), we found that the electronic states of QDs and every ZnO substrate are insensitive to any linker, while the frontier orbitals of L1-L4 (with increased delocalization) manifest a systematical negative-shift. Because of the lowest unoccupied molecular orbital (LUMO) of L1 compared to its counterparts aligned in the region of the virtual states of QDs or the substrate with a high density of states, it always yields a stronger electronic coupling with QDs and varied substrates. After characterization of the complete ZnO/linker/QD system, we found that the electron injection time (τ) vastly depends on both the linker and substrate. On the one hand, L1 bridged QDs and every substrate always achieve the shortest τ compared to their counterpart associated cases. On the other hand, NW supported systems always yield the shortest τ no matter what the linker is. Overall, the NW/L1/QD system achieves the fastest injection by ∼160 fs. This essentially stems from the shortest molecular length of L1 decreasing the distance between QDs and the substrate, subsequently improving the interfacial coupling. Meanwhile, the NW supported cases generate the less sensitive virtual states for both the QDs and NWs, ensuring a less variable interfacial coupling. These facts combined can provide understanding of the effects contributed from the linker and the oxide semiconductor morphology on charge transfer with the aim of choosing an appropriate component with fast directional electron injection.
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Affiliation(s)
- Wei-Lu Ding
- Beijing Key Laboratory of Cluster Science of Ministry of Education, Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China.
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16
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Teunis MB, Nagaraju M, Dutta P, Pu J, Muhoberac BB, Sardar R, Agarwal M. Elucidating the role of surface passivating ligand structural parameters in hole wave function delocalization in semiconductor cluster molecules. NANOSCALE 2017; 9:14127-14138. [PMID: 28902194 DOI: 10.1039/c7nr04874b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This article describes the mechanisms underlying electronic interactions between surface passivating ligands and (CdSe)34 semiconductor cluster molecules (SCMs) that facilitate band-gap engineering through the delocalization of hole wave functions without altering their inorganic core. We show here both experimentally and through density functional theory calculations that the expansion of the hole wave function beyond the SCM boundary into the ligand monolayer depends not only on the pre-binding energetic alignment of interfacial orbitals between the SCM and surface passivating ligands but is also strongly influenced by definable ligand structural parameters such as the extent of their π-conjugation [π-delocalization energy; pyrene (Py), anthracene (Anth), naphthalene (Naph), and phenyl (Ph)], binding mode [dithiocarbamate (DTC, -NH-CS2-), carboxylate (-COO-), and amine (-NH2)], and binding head group [-SH, -SeH, and -TeH]. We observe an unprecedentedly large ∼650 meV red-shift in the lowest energy optical absorption band of (CdSe)34 SCMs upon passivating their surface with Py-DTC ligands and the trend is found to be Ph- < Naph- < Anth- < Py-DTC. This shift is reversible upon removal of Py-DTC by triethylphosphine gold(i) chloride treatment at room temperature. Furthermore, we performed temperature-dependent (80-300 K) photoluminescence lifetime measurements, which show longer lifetime at lower temperature, suggesting a strong influence of hole wave function delocalization rather than carrier trapping and/or phonon-mediated relaxation. Taken together, knowledge of how ligands electronically interact with the SCM surface is crucial to semiconductor nanomaterial research in general because it allows the tuning of electronic properties of nanomaterials for better charge separation and enhanced charge transfer, which in turn will increase optoelectronic device and photocatalytic efficiencies.
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Affiliation(s)
- Meghan B Teunis
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, USA.
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17
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Thompson CM, Kodaimati M, Westmoreland D, Calzada R, Weiss EA. Electrostatic Control of Excitonic Energies and Dynamics in a CdS Quantum Dot through Reversible Protonation of Its Ligands. J Phys Chem Lett 2016; 7:3954-3960. [PMID: 27649043 DOI: 10.1021/acs.jpclett.6b01899] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This paper describes the pH dependence of the excitonic energies and dynamics of CdS quantum dots (QDs) capped with phosphonopropionate (PPA) in water. QDs capped with PPA carry a negative charge on their surfaces upon deprotonation of PPA above pH ∼ 8.5; the resultant electric field induces large changes in the QD's optical properties. Between pH 5.6 and 12.0, an increase in pH is accompanied by a 47-meV bathochromic shift in the bandgap of the QDs and a decrease in the Stokes shift by ∼4.3 meV/pH unit. An increase in the radiative recombination rate by a factor of 20.9 occurs on increasing the pH from 5.6 to 9.4. These observations are attributed to a shifting of the energy levels within the first exciton manifold, and are simulated using time-dependent density functional theory calculations on model Cd29S29 clusters surrounded by point charges.
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Affiliation(s)
- Christopher M Thompson
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Mohamad Kodaimati
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Dana Westmoreland
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Raul Calzada
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Emily A Weiss
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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18
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Lawrence KN, Dutta P, Nagaraju M, Teunis MB, Muhoberac BB, Sardar R. Dual Role of Electron-Accepting Metal-Carboxylate Ligands: Reversible Expansion of Exciton Delocalization and Passivation of Nonradiative Trap-States in Molecule-like CdSe Nanocrystals. J Am Chem Soc 2016; 138:12813-12825. [DOI: 10.1021/jacs.6b04888] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Katie N. Lawrence
- Department
of Chemistry and Chemical Biology, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Poulami Dutta
- Department
of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824, United States
| | - Mulpuri Nagaraju
- Department
of Chemistry and Chemical Biology, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Meghan B. Teunis
- Department
of Chemistry and Chemical Biology, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Barry B. Muhoberac
- Department
of Chemistry and Chemical Biology, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
| | - Rajesh Sardar
- Department
of Chemistry and Chemical Biology, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
- Integrated
Nanosystems Development Institute, Indiana University−Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States
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19
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Rabouw FT, de Mello Donega C. Excited-State Dynamics in Colloidal Semiconductor Nanocrystals. Top Curr Chem (Cham) 2016; 374:58. [PMID: 27573500 PMCID: PMC5480409 DOI: 10.1007/s41061-016-0060-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 07/23/2016] [Indexed: 11/29/2022]
Abstract
Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique size- and shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical–chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss the relevance of the different relaxation processes to a number of potential applications, such as photovoltaics and LEDs. The fundamental physical and chemical principles needed to control and understand the properties of colloidal semiconductor nanocrystals are also addressed.
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Affiliation(s)
- Freddy T Rabouw
- Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, PO Box 80000, 3508 TA, Utrecht, The Netherlands.,Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, PO Box 80000, 3508 TA, Utrecht, The Netherlands.,Optical Materials Engineering Laboratory, ETH Zurich, 8092, Zurich, Switzerland
| | - Celso de Mello Donega
- Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, PO Box 80000, 3508 TA, Utrecht, The Netherlands.
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20
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Harris RD, Bettis Homan S, Kodaimati M, He C, Nepomnyashchii AB, Swenson NK, Lian S, Calzada R, Weiss EA. Electronic Processes within Quantum Dot-Molecule Complexes. Chem Rev 2016; 116:12865-12919. [PMID: 27499491 DOI: 10.1021/acs.chemrev.6b00102] [Citation(s) in RCA: 168] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The subject of this review is the colloidal quantum dot (QD) and specifically the interaction of the QD with proximate molecules. It covers various functions of these molecules, including (i) ligands for the QDs, coupled electronically or vibrationally to localized surface states or to the delocalized states of the QD core, (ii) energy or electron donors or acceptors for the QDs, and (iii) structural components of QD assemblies that dictate QD-QD or QD-molecule interactions. Research on interactions of ligands with colloidal QDs has revealed that ligands determine not only the excited state dynamics of the QD but also, in some cases, its ground state electronic structure. Specifically, the article discusses (i) measurement of the electronic structure of colloidal QDs and the influence of their surface chemistry, in particular, dipolar ligands and exciton-delocalizing ligands, on their electronic energies; (ii) the role of molecules in interfacial electron and energy transfer processes involving QDs, including electron-to-vibrational energy transfer and the use of the ligand shell of a QD as a semipermeable membrane that gates its redox activity; and (iii) a particular application of colloidal QDs, photoredox catalysis, which exploits the combination of the electronic structure of the QD core and the chemistry at its surface to use the energy of the QD excited state to drive chemical reactions.
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Affiliation(s)
- Rachel D Harris
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Stephanie Bettis Homan
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Mohamad Kodaimati
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Chen He
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | | | - Nathaniel K Swenson
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Shichen Lian
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Raul Calzada
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Emily A Weiss
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
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21
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Yoon SJ, Guo Z, Dos Santos Claro PC, Shevchenko EV, Huang L. Direct Imaging of Long-Range Exciton Transport in Quantum Dot Superlattices by Ultrafast Microscopy. ACS NANO 2016; 10:7208-7215. [PMID: 27387010 DOI: 10.1021/acsnano.6b03700] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Long-range charge and exciton transport in quantum dot (QD) solids is a crucial challenge in utilizing QDs for optoelectronic applications. Here, we present a direct visualization of exciton diffusion in highly ordered CdSe QDs superlattices by mapping exciton population using ultrafast transient absorption microscopy. A temporal resolution of ∼200 fs and a spatial precision of ∼50 nm of this technique provide a direct assessment of the upper limit for exciton transport in QD solids. An exciton diffusion length of ∼125 nm has been visualized in the 3 ns experimental time window and an exciton diffusion coefficient of (2.5 ± 0.2) × 10(-2) cm(2) s(-1) has been measured for superlattices constructed from 3.6 nm CdSe QDs with center-to-center distance of 6.7 nm. The measured exciton diffusion constant is in good agreement with Förster resonance energy transfer theory. We have found that exciton diffusion is greatly enhanced in the superlattices over the disordered films with an order of magnitude higher diffusion coefficient, pointing toward the role of disorder in limiting transport. This study provides important understandings on energy transport mechanisms in both the spatial and temporal domains in QD solids.
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Affiliation(s)
- Seog Joon Yoon
- Radiation Laboratory, University of Notre Dame , Notre Dame, Indiana 46556, United States
- Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556, United States
| | - Zhi Guo
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
| | - Paula C Dos Santos Claro
- Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Elena V Shevchenko
- Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Libai Huang
- Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States
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22
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Lian S, Weinberg DJ, Harris RD, Kodaimati MS, Weiss EA. Subpicosecond Photoinduced Hole Transfer from a CdS Quantum Dot to a Molecular Acceptor Bound Through an Exciton-Delocalizing Ligand. ACS NANO 2016; 10:6372-6382. [PMID: 27281685 DOI: 10.1021/acsnano.6b02814] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This paper describes the enhancement of the rate of hole transfer from a photoexcited CdS quantum dot (QD), with radius R = 2.0 nm, to a molecular acceptor, phenothiazine (PTZ), by linking the donor and acceptor through a phenyldithiocarbamate (PTC) linker, which is known to lower the confinement energy of the excitonic hole. Upon adsorption of PTC, the bandgap of the QD decreases due to delocalization of the exciton, primarily the excitonic hole, into interfacial states of mixed QD/PTC character. This delocalization enables hole transfer from the QD to PTZ in <300 fs (within the instrument response of the laser system) when linked by PTC, but not when linked by a benzoate group, which has a similar length and conjugation as PTC but does not delocalize the excitonic hole. Comparison of the two systems was aided by quantification of the surface coverage of benzoate and PTC-linked PTZ by (1)H NMR. This work provides direct spectroscopic evidence of the enhancement of the rate of hole extraction from a colloidal QD through covalent linkage of a hole acceptor through an exciton-delocalizing ligand.
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Affiliation(s)
- Shichen Lian
- Department of Chemistry, Northwestern University , 2145 Sheridan Rd., Evanston, Illinois 60208-3113, United States
| | - David J Weinberg
- Department of Chemistry, Northwestern University , 2145 Sheridan Rd., Evanston, Illinois 60208-3113, United States
| | - Rachel D Harris
- Department of Chemistry, Northwestern University , 2145 Sheridan Rd., Evanston, Illinois 60208-3113, United States
| | - Mohamad S Kodaimati
- Department of Chemistry, Northwestern University , 2145 Sheridan Rd., Evanston, Illinois 60208-3113, United States
| | - Emily A Weiss
- Department of Chemistry, Northwestern University , 2145 Sheridan Rd., Evanston, Illinois 60208-3113, United States
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23
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Sowers KL, Hou Z, Peterson JJ, Swartz B, Pal S, Prezhdo O, Krauss TD. Photophysical Properties of CdSe/CdS core/shell quantum dots with tunable surface composition. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2015.09.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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24
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Lukose B, Clancy P. A feasibility study of unconventional planar ligand spacers in chalcogenide nanocrystals. Phys Chem Chem Phys 2016; 18:13781-93. [PMID: 26918246 DOI: 10.1039/c5cp07521a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The solar cell efficiency of chalcogenide nanocrystals (quantum dots) has been limited in the past by the insulation between neighboring quantum dots caused by intervening, often long-chain, aliphatic ligands. We have conducted a computationally based feasibility study to investigate the use of ultra-thin, planar, charge-conducting ligands as an alternative to traditional long passive ligands. Not only might these radically unconventional ligands decrease the mean distance between adjacent quantum dots, but, since they are charge-conducting, they have the potential to actively enhance charge migration. Our ab initio studies compare the binding energies, electronic energy gaps, and absorption characteristics for both conventional and unconventional ligands, such as phthalocyanines, porphyrins and coronene. This comparison identified these unconventional ligands with the exception of titanyl phthalocyanine, that bind to themselves more strongly than to the surface of the quantum dot, which is likely to be less desirable for enhancing charge transport. The distribution of finite energy levels of the bound system is sensitive to the ligand's binding site and the levels correspond to delocalized states. We also observed a trap state localized on a single Pb atom when a sulfur-containing phenyldithiocarbamate (PTC) ligand is attached to a slightly off-stoichiometric dot in a manner that the sulfur of the ligand completes stoichiometry of the bound system. Hence, this is indicative of the source of trap state when thio-based ligands are bound to chalcogenide nanocrystals. We also predict that titanyl phthalocyanine in a mix with chalcogenide dots of diameter ∼1.5 Å can form a donor-acceptor system.
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Affiliation(s)
- Binit Lukose
- School of Chemical and Biomolecular Engineering, Cornell University, 14853 Ithaca, NY, USA.
| | - Paulette Clancy
- School of Chemical and Biomolecular Engineering, Cornell University, 14853 Ithaca, NY, USA.
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25
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Aruda KO, Amin VA, Thompson CM, Lau B, Nepomnyashchii AB, Weiss EA. Description of the Adsorption and Exciton Delocalizing Properties of p-Substituted Thiophenols on CdSe Quantum Dots. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:3354-3364. [PMID: 27002248 DOI: 10.1021/acs.langmuir.6b00689] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This work describes the quantitative characterization of the interfacial chemical and electronic structure of CdSe quantum dots (QDs) coated in one of five p-substituted thiophenolates (X-TP, X = NH2, CH3O, CH3, Cl, or NO2), and the dependence of this structure on the p-substituent X. (1)H NMR spectra of mixtures of CdSe QDs and X-TPs yield the number of X-TPs bound to the surface of each QD. The binding data, in combination with the shift in the energy of the first excitonic peak of the QDs as a function of the surface coverage of X-TP and Raman and NMR analysis of the mixtures, indicate that X-TP binds to CdSe QDs in at least three modes, two modes that are responsible for exciton delocalization and a third mode that does not affect the excitonic energy. The first two modes involve displacement of OPA from the QD core, whereas the third mode forms cadmium-thiophenolate complexes that are not electronically coupled to the QD core. Fits to the data using the dual-mode binding model also yield the values of Δr1, the average radius of exciton delocalization due to binding of the X-TP in modes 1 and 2. A 3D parametrized particle-in-a-sphere model enables the conversion of the measured value of Δr1 for each X-TP to the height of the potential barrier that the ligand presents for tunneling of excitonic hole into the interfacial region. The height of this barrier increases from 0.3 to 0.9 eV as the substituent, X, becomes more electron-withdrawing.
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Affiliation(s)
- Kenneth O Aruda
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Victor A Amin
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Christopher M Thompson
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Bryan Lau
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Alexander B Nepomnyashchii
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Emily A Weiss
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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26
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Singhal P, Ghorpade PV, Shankarling GS, Singhal N, Jha SK, Tripathi RM, Ghosh HN. Exciton delocalization and hot hole extraction in CdSe QDs and CdSe/ZnS type 1 core shell QDs sensitized with newly synthesized thiols. NANOSCALE 2016; 8:1823-1833. [PMID: 26698125 DOI: 10.1039/c5nr07605f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady state absorption study suggests the exciton delocalization from CdSe QDs in the presence of the thiols. However similar features were not observed in the presence of a ZnS shell over a CdSe core, instead a broadening in the excitonic peak was observed with both APT and ADPT but not with AAT. This exciton delocalization and broadening in the excitonic peak was also confirmed by ultrafast transient absorption studies. Steady state and time resolved emission studies show hole transfer from photo-excited QDs and CSQDs to the thiols. A signature of hot hole extraction was observed in transient absorption studies which was confirmed by fluorescence upconversion studies. Both hot and thermalized hole transfer rates from CdSe QDs and CdSe/ZnS CSQDs to the thiols were determined using the fluorescence up-conversion technique. Experiments with different ZnS shell thicknesses have been carried out which suggest that hole transfer is possible till 2.5 monolayer of the ZnS shell. To the best of our knowledge we are reporting for the first time the extraction of hot holes from CdSe/ZnS type I CSQDs by a molecular adsorbate.
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Affiliation(s)
- Pallavi Singhal
- Health Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
| | - Prashant V Ghorpade
- Department of Dyestuff Technology, Institute Of Chemical Technology, Mumbai, India.
| | | | - Nancy Singhal
- Department of Chemistry, Indian Institute of Technology, Mumbai, India
| | - Sanjay K Jha
- Health Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
| | - Raj M Tripathi
- Health Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
| | - Hirendra N Ghosh
- Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
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Harris RD, Amin VA, Lau B, Weiss EA. Role of Interligand Coupling in Determining the Interfacial Electronic Structure of Colloidal CdS Quantum Dots. ACS NANO 2016; 10:1395-1403. [PMID: 26727219 DOI: 10.1021/acsnano.5b06837] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Displacement of cadmium oleate (Cd(oleate)2) ligands for the exciton-delocalizing ligand 4-hexylphenyldithiocarbamate (C6-PTC) on the surfaces of CdS quantum dots (QDs) causes a decrease in the band gap (Eg) of the QD of ∼100 meV for QDs with a radius of 1.9 nm and ∼50 meV for QDs with a radius of 2.5 nm. The primary mechanism of this decrease in band gap, deduced in previous work, is a decrease in the confinement barrier for the excitonic hole. The increase in apparent excitonic radius of the QD that corresponds to this decrease in Eg is denoted ΔR. The dependence of ΔR on the surface coverage of C6-PTC, measured by (1)H NMR spectroscopy, appears to be nonlinear. Calculations of the excitonic energy of a CdS QD upon displacement of native insulating ligands with exciton-delocalizing ligands using a 3D spherical potential well model show that this response includes the contributions to ΔR from both isolated, bound C6-PTC ligands and groups of adjacent C6-PTC ligands. Fits to the experimental plots of ΔR vs surface coverage of C6-PTC with a statistical model that includes the probability of formation of clusters of bound C6-PTC on the QD surface allow for the extraction of the height of the confinement barrier presented by a single, isolated C6-PTC molecule to the excitonic hole. This barrier height is less than 0.6 eV for QDs with a radius of 1.9 nm and between 0.6 and 1.2 eV for QDs with a radius of 2.5 nm.
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Affiliation(s)
- Rachel D Harris
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Victor A Amin
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Bryan Lau
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Emily A Weiss
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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28
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Jethi L, Mack TG, Krause MM, Drake S, Kambhampati P. The Effect of Exciton-Delocalizing Thiols on Intrinsic Dual Emitting Semiconductor Nanocrystals. Chemphyschem 2016; 17:665-9. [PMID: 26752223 DOI: 10.1002/cphc.201501049] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Indexed: 11/07/2022]
Affiliation(s)
- Lakshay Jethi
- Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A0B8, Canada
| | - Timothy G Mack
- Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A0B8, Canada
| | - Michael M Krause
- Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A0B8, Canada
| | - Sebastian Drake
- Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A0B8, Canada
| | - Patanjali Kambhampati
- Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A0B8, Canada.
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29
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Reeves KG, Schleife A, Correa AA, Kanai Y. Role of Surface Termination on Hot Electron Relaxation in Silicon Quantum Dots: A First-Principles Dynamics Simulation Study. NANO LETTERS 2015; 15:6429-6433. [PMID: 26331672 DOI: 10.1021/acs.nanolett.5b01707] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The role of surface termination on phonon-mediated relaxation of an excited electron in quantum dots was investigated using first-principles simulations. The surface terminations of a silicon quantum dot with hydrogen and fluorine atoms lead to distinctively different relaxation behaviors, and the fluorine termination shows a nontrivial relaxation process. The quantum confined electronic states are significantly affected by the surface of the quantum dot, and we find that a particular electronic state dictates the relaxation behavior through its infrequent coupling to neighboring electronic states. Dynamical fluctuation of this electronic state results in a slow shuttling behavior within the manifold of unoccupied electronic states, controlling the overall dynamics of the excited electron with its characteristic frequency of this shuttling behavior. The present work revealed a unique role of surface termination, dictating the hot electron relaxation process in quantum-confined systems in the way that has not been considered previously.
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Affiliation(s)
- Kyle G Reeves
- Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27514, United States
| | - André Schleife
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , Champaign, Illinois 61820, United States
| | - Alfredo A Correa
- Condensed Matter and Materials Division, Lawrence Livermore National Laboratory , Livermore, California 94550, United States
| | - Yosuke Kanai
- Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27514, United States
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30
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Azpiroz JM, De Angelis F. Ligand Induced Spectral Changes in CdSe Quantum Dots. ACS APPLIED MATERIALS & INTERFACES 2015; 7:19736-19745. [PMID: 26289823 DOI: 10.1021/acsami.5b05418] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The rational design of ligand molecules has earned lots of attention as an elegant means to tailor the electronic and optical properties of semiconductor quantum dots (QDs). Aromatic dithiocarbamate molecules, in particular, are known to greatly influence the optoelectronic properties of CdSe QDs, red-shifting the absorption features and enhancing the photoluminescence. Here, we present an integrated computational study, which combines ab initio molecular dynamics and excited state calculations including thousands of excitations, aimed at understanding the impact of this kind of surface ligand on the optoelectronic properties of CdSe QDs. We demonstrate that the valence electronic states of the dithiocarbamate molecules, mostly localized in the anchoring moiety, are responsible for the red-shift of the absorption features of capped CdSe QDs. Ligands develop interfacial electronic states close to the band edges of the CdSe, which enhance the absorption features of the QD and might open new channels for the radiative decay from the excited state, improving optical emission. Hybridized QD/ligand states could also funnel interfacial charge transfer between the inorganic core and surface molecules, a process that lies at the heart of many photovoltaic and photocatalytic devices. This work may pave the way toward the design of new capping ligands that, adsorbed on the QD surface, could provide control over the optoelectronic properties of the semiconductor core.
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Affiliation(s)
- Jon M Azpiroz
- Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR) , Via Elce di Sotto 8, 06123, Perugia, Italy
- Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), and Donostia International Physics Center (DIPC), P. K. 1072, 20080 Donostia, Euskadi, Spain
| | - Filippo De Angelis
- Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR) , Via Elce di Sotto 8, 06123, Perugia, Italy
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Krause MM, Kambhampati P. Linking surface chemistry to optical properties of semiconductor nanocrystals. Phys Chem Chem Phys 2015; 17:18882-94. [DOI: 10.1039/c5cp02173a] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This perspective gives insight into how the chemistry occurring at the surface of semiconductor nanocrystals is crucial to tailoring their optical properties to a myriad of applications.
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