1
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Nowik-Boltyk EM, Junghoefer T, Giangrisostomi E, Ovsyannikov R, Shu C, Rajca A, Droghetti A, Casu MB. Radical-Induced Changes in Transition Metal Interfacial Magnetic Properties: A Blatter Derivative on Polycrystalline Cobalt. Angew Chem Int Ed Engl 2024:e202403495. [PMID: 38843268 DOI: 10.1002/anie.202403495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Indexed: 07/23/2024]
Abstract
In this work, we study the interface obtained by depositing a monolayer of a Blatter radical derivative on polycrystalline cobalt. By examining the occupied and unoccupied states at the interface, using soft X-ray techniques, combined with electronic structure calculations, we could simultaneously determine the electronic structure of both the molecular and ferromagnetic sides of the interface, thus obtaining a full understanding of the interfacial magnetic properties. We found that the molecule is strongly hybridized with the surface. Changes in the core level spectra reflect the modification of the molecule and the cobalt electronic structures inducing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules which, in turn, lose their radical character. Our method allowed us to screen, beforehand, organic/ferromagnetic interfaces given their potential applications in spintronics.
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Affiliation(s)
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076, Tübingen, Germany
| | - Erika Giangrisostomi
- Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin, 12489, Berlin, Germany
| | - Ruslan Ovsyannikov
- Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin, 12489, Berlin, Germany
| | - Chan Shu
- Department of Chemistry, University of Nebraska, Lincoln, NE 68588, United States
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, NE 68588, United States
| | - Andrea Droghetti
- School of Physics and CRANN, Trinity College, the University of Dublin, Dublin, D02, Ireland
| | - M Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076, Tübingen, Germany
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2
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Nowik-Boltyk EM, Junghoefer T, Glaser M, Giangrisostomi E, Ovsyannikov R, Zhang S, Shu C, Rajca A, Calzolari A, Casu MB. Long-Term Degradation Mechanisms in Application-Implemented Radical Thin Films. ACS APPLIED MATERIALS & INTERFACES 2023. [PMID: 37319383 DOI: 10.1021/acsami.3c02057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Blatter radical derivatives are very attractive due to their potential applications, ranging from batteries to quantum technologies. In this work, we focus on the latest insights regarding the fundamental mechanisms of radical thin film (long-term) degradation, by comparing two Blatter radical derivatives. We find that the interaction with different contaminants (such as atomic H, Ar, N, and O and molecular H2, N2, O2, H2O, and NH2) affects the chemical and magnetic properties of the thin films upon air exposure. Also, the radical-specific site, where the contaminant interaction takes place, plays a role. Atomic H and NH2 are detrimental to the magnetic properties of Blatter radicals, while the presence of molecular water influences more specifically the magnetic properties of the diradical thin films, and it is believed to be the major cause of the shorter diradical thin film lifetime in air.
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Affiliation(s)
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Mathias Glaser
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Erika Giangrisostomi
- Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin, 12489 Berlin, Germany
| | - Ruslan Ovsyannikov
- Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin, 12489 Berlin, Germany
| | - Shuyang Zhang
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Chan Shu
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, United States
| | | | - M Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
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3
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Shu C, Pink M, Junghoefer T, Nadler E, Rajca S, Casu MB, Rajca A. Synthesis and Thin Films of Thermally Robust Quartet ( S = 3/2) Ground State Triradical. J Am Chem Soc 2021; 143:5508-5518. [PMID: 33787241 DOI: 10.1021/jacs.1c01305] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
High-spin (S = 3/2) organic triradicals may offer enhanced properties with respect to several emerging technologies, but those synthesized to date typically exhibit small doublet quartet energy gaps and/or possess limited thermal stability and processability. We report a quartet ground state triradical 3, synthesized by a Pd(0)-catalyzed radical-radical cross-coupling reaction, which possesses two doublet-quartet energy gaps, ΔEDQ ≈ 0.2-0.3 kcal mol-1 and ΔEDQ2 ≈ 1.2-1.8 kcal mol-1. The triradical has a 70+% population of the quartet ground state at room temperature and good thermal stability with onset of decomposition at >160 °C under an inert atmosphere. Magnetic properties of 3 are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical 3 is evaporated under ultrahigh vacuum to form thin films of intact triradicals on silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy. AFM and SEM images of the ∼1 nm thick films indicate that the triradical molecules form islands on the substrate. The films are stable under ultrahigh vacuum for at least 17 h but show onset of decomposition after 4 h at ambient conditions. The drop-cast films are less prone to degradation in air and have a longer lifetime.
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Affiliation(s)
- Chan Shu
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Maren Pink
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Elke Nadler
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Suchada Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
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4
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Hande AA, Darrigan C, Bartos P, Baylère P, Pietrzak A, Kaszyński P, Chrostowska A. UV-photoelectron spectroscopy of stable radicals: the electronic structure of planar Blatter radicals as materials for organic electronics. Phys Chem Chem Phys 2020; 22:23637-23644. [PMID: 33111728 DOI: 10.1039/d0cp03896b] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic structure of Blatter radicals and a series of C(10)-substituted derivatives of 2-phenyl-3H-[1,2,4]triazino[5,6,1-kl]phenoxazin-3-yl (planar Blatter radicals) containing H, F, Cl, Br, CN, CF3 and OMe substituents was investigated by gas phase UV-photoelectron spectroscopy. The energy of the SOMO of the radicals, determined to be about 6.5 eV, was correlated with their electrochemical oxidation potentials, E0/+11/2, relative to the Fc/Fc+ couple in CH2Cl2 giving the correction of 6.60(1) eV. The optical band gap Eoptg ∼ 1.7 eV of the radicals yielded the electronic transport gap, Eelg, of about 2.1 eV, which is similar to the electronic parameters of pentacene. The radicals were analyzed by EPR spectroscopy and single crystal XRD methods, and all experimental data were compared to DFT computational results obtained at the CAM-B3LYP/6-311G(d,p) level of theory.
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Affiliation(s)
- Aniket A Hande
- Université de Pau et des Pays de l'Adour E2S UPPA, CNRS, IPREM UMR 5254, 64000, Pau, France
| | - Clovis Darrigan
- Université de Pau et des Pays de l'Adour E2S UPPA, CNRS, IPREM UMR 5254, 64000, Pau, France
| | - Paulina Bartos
- Faculty of Chemistry, University of Łódź, Tamka 12, 91-403 Łódź, Poland.
| | - Patrick Baylère
- Université de Pau et des Pays de l'Adour E2S UPPA, CNRS, IPREM UMR 5254, 64000, Pau, France
| | - Anna Pietrzak
- Faculty of Chemistry, Łódź University of Technology, Żeromskiego 116, 90-924 Łódź, Poland and Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37130, USA
| | - Piotr Kaszyński
- Faculty of Chemistry, University of Łódź, Tamka 12, 91-403 Łódź, Poland. and Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37130, USA and Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, 90-363 Łódź, Poland
| | - Anna Chrostowska
- Université de Pau et des Pays de l'Adour E2S UPPA, CNRS, IPREM UMR 5254, 64000, Pau, France
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5
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Junghoefer T, Nowik-Boltyk EM, de Sousa JA, Giangrisostomi E, Ovsyannikov R, Chassé T, Veciana J, Mas-Torrent M, Rovira C, Crivillers N, Casu MB. Stability of radical-functionalized gold surfaces by self-assembly and on-surface chemistry. Chem Sci 2020; 11:9162-9172. [PMID: 34123165 PMCID: PMC8163401 DOI: 10.1039/d0sc03399e] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 08/10/2020] [Indexed: 11/23/2022] Open
Abstract
We have investigated the radical functionalization of gold surfaces with a derivative of the perchlorotriphenylmethyl (PTM) radical using two methods: by chemisorption from the radical solution and by on-surface chemical derivation from a precursor. We have investigated the obtained self-assembled monolayers by photon-energy dependent X-ray photoelectron spectroscopy. Our results show that the molecules were successfully anchored on the surfaces. We have used a robust method that can be applied to a variety of materials to assess the stability of the functionalized interface. The monolayers are characterized by air and X-ray beam stability unprecedented for films of organic radicals. Over very long X-ray beam exposure we observed a dynamic nature of the radical-Au complex. The results clearly indicate that (mono)layers of PTM radical derivatives have the necessary stability to withstand device applications.
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Affiliation(s)
- Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen 72076 Tübingen Germany
| | | | - J Alejandro de Sousa
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Campus de la UAB 08193 Bellaterra Spain
- Laboratorio de Electroquímica, Departamento de Química, Facultad de Ciencias, Universidad de los Andes 5101 Mérida Venezuela
| | | | - Ruslan Ovsyannikov
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) 12489 Berlin Germany
| | - Thomas Chassé
- Institute of Physical and Theoretical Chemistry, University of Tübingen 72076 Tübingen Germany
| | - Jaume Veciana
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Campus de la UAB 08193 Bellaterra Spain
| | - Marta Mas-Torrent
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Campus de la UAB 08193 Bellaterra Spain
| | - Concepció Rovira
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Campus de la UAB 08193 Bellaterra Spain
| | - Núria Crivillers
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Campus de la UAB 08193 Bellaterra Spain
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen 72076 Tübingen Germany
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6
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Yamada A, Abe M, Nishimura Y, Ishizaka S, Namba M, Nakashima T, Shimoji K, Hattori N. Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells. Beilstein J Org Chem 2019; 15:863-873. [PMID: 31019579 PMCID: PMC6466695 DOI: 10.3762/bjoc.15.84] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 03/16/2019] [Indexed: 12/14/2022] Open
Abstract
Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive character, 2,2,6,6-tetramethyl-1-(1-(2-(4-nitrophenyl)benzofuran-6-yl)ethoxy)piperidine (2a) and its regioisomer 2b, were designed and synthesized. The one-photon (OP) (365 ± 10 nm) and TP (710–760 nm) triggered release (i.e., uncaging) of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical under air atmosphere were discovered. The quantum yields for the release of the TEMPO radical were 2.5% (2a) and 0.8% (2b) in benzene at ≈1% conversion of 2, and 13.1% (2a) and 12.8% (2b) in DMSO at ≈1% conversion of 2. The TP uncaging efficiencies were determined to be 1.1 GM at 740 nm for 2a and 0.22 GM at 730 nm for 2b in benzene. The cytocidal effect of compound 2a on lung cancer cells under photolysis conditions was also assessed to test the efficacy as anticancer agents. In a medium containing 100 μg mL−1 of 2a exposed to light, the number of living cells decreased significantly compared to the unexposed counterparts (65.8% vs 85.5%).
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Affiliation(s)
- Ayato Yamada
- Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
| | - Manabu Abe
- Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Hiroshima Research Centre for Photo-Drug-Delivery Systems (HiU-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,JST-CREST, K's Gobancho 6F, 7, Gobancho, Chiyoda-ku, Tokyo 102-0075, Japan
| | - Yoshinobu Nishimura
- Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
| | - Shoji Ishizaka
- Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Hiroshima Research Centre for Photo-Drug-Delivery Systems (HiU-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
| | - Masashi Namba
- Hiroshima Research Centre for Photo-Drug-Delivery Systems (HiU-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan
| | - Taku Nakashima
- Hiroshima Research Centre for Photo-Drug-Delivery Systems (HiU-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan
| | - Kiyofumi Shimoji
- Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan
| | - Noboru Hattori
- Hiroshima Research Centre for Photo-Drug-Delivery Systems (HiU-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan
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7
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Gallagher N, Zhang H, Junghoefer T, Giangrisostomi E, Ovsyannikov R, Pink M, Rajca S, Casu MB, Rajca A. Thermally and Magnetically Robust Triplet Ground State Diradical. J Am Chem Soc 2019; 141:4764-4774. [PMID: 30816035 DOI: 10.1021/jacs.9b00558] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High spin ( S = 1) organic diradicals may offer enhanced properties with respect to several emerging technologies, but typically exhibit low singlet triplet energy gaps and possess limited thermal stability. We report triplet ground state diradical 2 with a large singlet-triplet energy gap, Δ EST ≥ 1.7 kcal mol-1, leading to nearly exclusive population of triplet ground state at room temperature, and good thermal stability with onset of decomposition at ∼160 °C under inert atmosphere. Magnetic properties of 2 and the previously prepared diradical 1 are characterized by SQUID magnetometry of polycrystalline powders, in polystyrene glass, and in other matrices. Polycrystalline diradical 2 forms a novel one-dimensional (1D) spin-1 ( S = 1) chain of organic radicals with intrachain antiferromagnetic coupling of J'/ k = -14 K, which is associated with the N···N and N···O intermolecular contacts. The intrachain antiferromagnetic coupling in 2 is by far strongest among all studied 1D S = 1 chains of organic radicals, which also makes 1D S = 1 chains of 2 most isotropic, and therefore an excellent system for studies of low-dimensional magnetism. In polystyrene glass and in frozen benzene or dibutyl phthalate solution, both 1 and 2 are monomeric. Diradical 2 is thermally robust and is evaporated under ultrahigh vacuum to form thin films of intact diradicals on silicon substrate, as demonstrated by X-ray photoelectron spectroscopy. Based on C-K NEXAFS spectra and AFM images of the ∼1.5 nm thick films, the diradical molecules form islands on the substrate with molecules stacked approximately along the crystallographic a-axis. The films are stable under ultrahigh vacuum for at least 60 h but show signs of decomposition when exposed to ambient conditions for 7 h.
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Affiliation(s)
- Nolan Gallagher
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
| | - Hui Zhang
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen , 72076 Tübingen , Germany
| | - Erika Giangrisostomi
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) , Albert-Einstein-Str 15 , 12489 Berlin , Germany
| | - Ruslan Ovsyannikov
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) , Albert-Einstein-Str 15 , 12489 Berlin , Germany
| | - Maren Pink
- Department of Chemistry , Indiana University , Bloomington , Indiana 47405-7102 , United States
| | - Suchada Rajca
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen , 72076 Tübingen , Germany
| | - Andrzej Rajca
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
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8
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Ciccullo F, Calzolari A, Bader K, Neugebauer P, Gallagher NM, Rajca A, van Slageren J, Casu MB. Interfacing a Potential Purely Organic Molecular Quantum Bit with a Real-Life Surface. ACS APPLIED MATERIALS & INTERFACES 2019; 11:1571-1578. [PMID: 30520295 DOI: 10.1021/acsami.8b16061] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
By using a multidisciplinary and multitechnique approach, we have addressed the issue of attaching a molecular quantum bit to a real surface. First, we demonstrate that an organic derivative of the pyrene-Blatter radical is a potential molecular quantum bit. Our study of the interface of the pyrene-Blatter radical with a copper-based surface reveals that the spin of the interface layer is not canceled by the interaction with the surface and that the Blatter radical is resistant in presence of molecular water. Although the measured pyrene-Blatter derivative quantum coherence time is not the highest value known, this molecule is known as a "super stable" radical. Conversely, other potential qubits show poor thin film stability upon air exposure. Therefore, we discuss strategies to make molecular systems candidates as qubits competitive, bridging the gap between potential and real applications.
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Affiliation(s)
- Francesca Ciccullo
- Institute of Physical and Theoretical Chemistry , University of Tübingen , 72076 Tübingen , Germany
| | - Arrigo Calzolari
- CNR-NANO Istituto Nanoscienze , Centro S3 , 41125 Modena , Italy
| | - Katharina Bader
- Institute of Physical Chemistry , University of Stuttgart , 70569 Stuttgart , Germany
| | - Petr Neugebauer
- Institute of Physical Chemistry , University of Stuttgart , 70569 Stuttgart , Germany
- Central European Institute of Technology, CEITEC BUT , Purkyňova 656/123 , 61600 Brno , Czech Republic
| | - Nolan M Gallagher
- Department of Chemistry , University of Nebraska-Lincoln , Lincoln , Nebraska 68588-0304 , United States
| | - Andrzej Rajca
- Department of Chemistry , University of Nebraska-Lincoln , Lincoln , Nebraska 68588-0304 , United States
| | - Joris van Slageren
- Institute of Physical Chemistry , University of Stuttgart , 70569 Stuttgart , Germany
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry , University of Tübingen , 72076 Tübingen , Germany
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9
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Abstract
In the last decade technology has brought significant changes to our lives, including new habits and a new view on social relationships. These technological innovations are based on several factors, one of which is miniaturization. This was made possible also due to the discovery and synthesis of new materials with characteristics at the nanoscale that are designed for specific purposes. This "on purpose" approach, joined to the development of preparation and growth methods, has led to use of thin films rather than bulk materials in devices. Using thin films makes devices easier to produce, and using films for coating protects the devices and gives specific properties to surfaces. For several decades thin films, surfaces, and interfaces have been intensively investigated. Indeed, device performances rely on the optimized match of thin films of different natures, such as organic and inorganic semiconductors and metals for contacts. Surprisingly, in comparison, little attention has been devoted to the deposition of organic radicals on a substrate. This might be because these materials are considered not stable enough for evaporation. In this work, we demonstrate that it is possible to evaporate and deposit organic radicals onto well-defined surfaces under controlled conditions, without degradation. Using soft X-ray spectroscopies, performed also at synchrotrons, we investigate thin film processes, surfaces, and interfaces at the nanoscale, when organic radicals are deposited on metal and metal oxide surfaces. We suggest how to design organic radicals bearing in mind the thermodynamic factors that govern thin film stability, with the purpose of obtaining not only a chemically stable radical, but also stable thin films. We investigate the thermal and air stability of the deposited films, and we explore the influence of the surface/radical chemical bond and the role of surface defects on the magnetic moment at the interface. We find that organic radicals are physisorbed and keep their magnetic moment on inert and passivated surfaces such as Au(111) and Al2O3(112̅0) single crystals, SiO2, and ideal TiO2(110) single crystals, while defective sites such as oxygen vacancies or the presence of OH groups lead to chemisorption of the organic radicals on the surface with quenching of their magnetic moment. Our work shows that the use of X-ray based techniques represents a powerful approach to reveal the mechanisms governing complex interfaces, such as radical/metal and radical/metal-oxide, where it is important to describe both charge and spin behavior (spinterfaces). It also makes it possible to conceive new experiments to investigate the magnetic character of the thin films versus their structural properties, toward tuning the arrangement of the molecules in films. Controlling the molecular arrangement will give the opportunity to tune the mutual position and orientation of the molecules, that is, of the single magnetic moments in the films, "imprinting" their magnetic properties. A deep understanding of stable radical/inorganic spinterfaces may open the way to use radicals in solid state devices or as quantum bits with dedicated configurations, as proposed for other molecular quantum bits, and in spin-based electronics.
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Affiliation(s)
- M. Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
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10
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Ciccullo F, Gallagher NM, Geladari O, Chassé T, Rajca A, Casu MB. A Derivative of the Blatter Radical as a Potential Metal-Free Magnet for Stable Thin Films and Interfaces. ACS APPLIED MATERIALS & INTERFACES 2016; 8:1805-1812. [PMID: 26727145 DOI: 10.1021/acsami.5b09693] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Organic radicals are fascinating materials because of their unique properties, which make them suitable for a variety of applications. Their synthesis may be challenging, and big efforts have focused on chemical stability. However, introducing a new material in electronics not only requires chemically stable molecules but also stable monolayers and thin films in view of their use in devices. In this work, we have investigated the thin films of a derivative of the Blatter radical that was synthesized bearing in mind the thermodynamic factors that govern thin film stability. We have proved our concept by investigating the electronic structure, the paramagnetic character, and stability of the obtained films under UHV and ambient conditions by in situ X-ray photoelectron spectroscopy, ex situ atomic force microscopy, and electron paramagnetic resonance spectroscopy.
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Affiliation(s)
- F Ciccullo
- Institute of Physical and Theoretical Chemistry, University of Tübingen , Auf der Morgenstelle 18, D-72076 Tübingen, Germany
| | - N M Gallagher
- Department of Chemistry, University of Nebraska , Lincoln, Nebraska 68588-0304, United States
| | - O Geladari
- Institute of Physical and Theoretical Chemistry, University of Tübingen , Auf der Morgenstelle 18, D-72076 Tübingen, Germany
| | - T Chassé
- Institute of Physical and Theoretical Chemistry, University of Tübingen , Auf der Morgenstelle 18, D-72076 Tübingen, Germany
| | - A Rajca
- Department of Chemistry, University of Nebraska , Lincoln, Nebraska 68588-0304, United States
| | - M B Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen , Auf der Morgenstelle 18, D-72076 Tübingen, Germany
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