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Rai V, Gerhard L, Balzer N, Valášek M, Holzer C, Yang L, Wegener M, Rockstuhl C, Mayor M, Wulfhekel W. Activating Electroluminescence of Charged Naphthalene Diimide Complexes Directly Adsorbed on a Metal Substrate. PHYSICAL REVIEW LETTERS 2023; 130:036201. [PMID: 36763403 DOI: 10.1103/physrevlett.130.036201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 09/02/2022] [Accepted: 12/13/2022] [Indexed: 06/18/2023]
Abstract
Electroluminescence from single molecules adsorbed on a conducting surface imposes conflicting demands for the molecule-electrode coupling. To conduct electrons, the molecular orbitals need to be hybridized with the electrodes. To emit light, they need to be decoupled from the electrodes to prevent fluorescence quenching. Here, we show that fully quenched 2,6-core-substituted naphthalene diimide derivative in a self-assembled monolayer directly deposited on a Au(111) surface can be activated with the tip of a scanning tunneling microscope to decouple the relevant frontier orbitals from the metallic substrate. In this way, individual molecules can be driven from a strongly hybridized state with quenched luminescence to a light-emitting state. The emission performance compares in terms of quantum efficiency, stability, and reproducibility to that of single molecules deposited on thin insulating layers. Quantum chemical calculations suggest that the emitted light originates from the singly charged cationic pair of the molecules.
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Affiliation(s)
- Vibhuti Rai
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Lukas Gerhard
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Nico Balzer
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Michal Valášek
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
| | - Christof Holzer
- Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany
| | - Liang Yang
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany
| | - Martin Wegener
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany
| | - Carsten Rockstuhl
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
- Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany
| | - Marcel Mayor
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
- Department of Chemistry, University of Basel, St. Johannsring 19, CH-4056 Basel, Switzerland
- Lehn Institute of Functional Materials (LIFM), Sun Yat-Sen University (SYSU), Xingang West Road, Guangzhou, China
| | - Wulf Wulfhekel
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), D-76128 Karlsruhe, Germany
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Light-Driven Charge Transport and Optical Sensing in Molecular Junctions. NANOMATERIALS 2022; 12:nano12040698. [PMID: 35215024 PMCID: PMC8878161 DOI: 10.3390/nano12040698] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 02/15/2022] [Accepted: 02/17/2022] [Indexed: 12/11/2022]
Abstract
Probing charge and energy transport in molecular junctions (MJs) has not only enabled a fundamental understanding of quantum transport at the atomic and molecular scale, but it also holds significant promise for the development of molecular-scale electronic devices. Recent years have witnessed a rapidly growing interest in understanding light-matter interactions in illuminated MJs. These studies have profoundly deepened our knowledge of the structure–property relations of various molecular materials and paved critical pathways towards utilizing single molecules in future optoelectronics applications. In this article, we survey recent progress in investigating light-driven charge transport in MJs, including junctions composed of a single molecule and self-assembled monolayers (SAMs) of molecules, and new opportunities in optical sensing at the single-molecule level. We focus our attention on describing the experimental design, key phenomena, and the underlying mechanisms. Specifically, topics presented include light-assisted charge transport, photoswitch, and photoemission in MJs. Emerging Raman sensing in MJs is also discussed. Finally, outstanding challenges are explored, and future perspectives in the field are provided.
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Balzer N, Lukášek J, Valášek M, Rai V, Sun Q, Gerhard L, Wulfhekel W, Mayor M. Synthesis and Surface Behaviour of NDI Chromophores Mounted on a Tripodal Scaffold: Towards Self-Decoupled Chromophores for Single-Molecule Electroluminescence. Chemistry 2021; 27:12144-12155. [PMID: 34152041 PMCID: PMC8457086 DOI: 10.1002/chem.202101264] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Indexed: 12/01/2022]
Abstract
This paper reports the efficient synthesis, absorption and emission spectra, and the electrochemical properties of a series of 2,6-disubstituted naphthalene-1,4,5,8-tetracarboxdiimide (NDI) tripodal molecules with thioacetate anchors for their surface investigations. Our studies showed that, in particular, the pyrrolidinyl group with its strong electron-donating properties enhanced the fluorescence of such core-substituted NDI chromophores and caused a significant bathochromic shift in the absorption spectrum with a correspondingly narrowed bandgap of 1.94 eV. Cyclic voltammetry showed the redox properties of NDIs to be influenced by core substituents. The strong electron-donating character of pyrrolidine substituents results in rather high HOMO and LUMO levels of -5.31 and -3.37 eV when compared with the parental unsubstituted NDI. UHV-STM measurements of a sub-monolayer of the rigid tripodal NDI chromophores spray deposited on Au(111) show that these molecules mainly tend to adsorb flat in a pairwise fashion on the surface and form unordered films. However, the STML experiments also revealed a few molecular clusters, which might consist of upright oriented molecules protruding from the molecular island and show electroluminescence photon spectra with high electroluminescence yields of up to 6×10-3 . These results demonstrate the promising potential of the NDI tripodal chromophores for the fabrication of molecular devices profiting from optical features of the molecular layer.
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Affiliation(s)
- Nico Balzer
- Institute of NanotechnologyKarlsruhe Institute of TechnologyP.O. Box 364076021KarlsruheGermany
| | - Jan Lukášek
- Institute of NanotechnologyKarlsruhe Institute of TechnologyP.O. Box 364076021KarlsruheGermany
| | - Michal Valášek
- Institute of NanotechnologyKarlsruhe Institute of TechnologyP.O. Box 364076021KarlsruheGermany
| | - Vibhuti Rai
- Institute of Quantum Materials and TechnologiesKarlsruhe Institute of Technology76021KarlsruheGermany
| | - Qing Sun
- Institute of Quantum Materials and TechnologiesKarlsruhe Institute of Technology76021KarlsruheGermany
| | - Lukas Gerhard
- Institute of Quantum Materials and TechnologiesKarlsruhe Institute of Technology76021KarlsruheGermany
| | - Wulf Wulfhekel
- Institute of Quantum Materials and TechnologiesKarlsruhe Institute of Technology76021KarlsruheGermany
- Physikalisches InstitutKarlsruhe Institute of TechnologyWolfgang-Gaede-Straße 176131KarlsruheGermany
| | - Marcel Mayor
- Institute of NanotechnologyKarlsruhe Institute of TechnologyP.O. Box 364076021KarlsruheGermany
- Department of ChemistryUniversity of BaselSt. Johanns-Ring 194056BaselSwitzerland
- Lehn Institute of Functional MaterialsSchool of ChemistrySun Yat-Sen UniversityGuangzhou, Guangdong510275P. R. China
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