Porphyrin-fused graphene nanoribbons
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-03-08 |
| Journal | Nature Chemistry |
| Authors | Qiang Chen, Alessandro Lodi, Heng Zhang, Alex Gee, Hai I. Wang |
| Institutions | University of Waterloo, Max Planck Institute for Polymer Research |
| Citations | 52 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research details the successful solution-phase synthesis and characterization of Porphyrin-fused Graphene Nanoribbons (PGNRs), opening new avenues for engineerable electronic and magnetic materials.
- Novel Synthesis: Achieved scalable, solution-phase synthesis of PGNRs (PGNRb) via Yamamoto polymerization followed by cyclodehydrogenation, yielding long chains with an average length of 85 nm (>100 nm maximum).
- Tunable Structure: The PGNR backbone incorporates metalloporphyrins (Ni(II)) fused into a twisted, fjord-edged GNR structure, allowing the transposition of coordination chemistry into the conjugated backbone.
- Narrow Bandgap: The material exhibits a narrow optical bandgap of approximately 1.0 eV, one of the lowest reported for solution-synthesized GNRs, with absorption extending to 1,600 nm.
- High Charge Mobility: Contact-free terahertz spectroscopy measured a high local charge mobility of 450 ± 60 cm2 V-1 s-1, suggesting superior short-range transport compared to pure carbon GNRs.
- Ambipolar FET Performance: PGNRs function as ambipolar field-effect transistors (FETs) at room temperature, showing appealing switching behavior (ION/IOFF â 103) and high field-effect mobilities (up to 40 cm2 V-1 s-1).
- Quantum Control: Devices fabricated as single-electron transistors (SETs) at millikelvin temperatures display multiple Coulomb diamonds and regions of negative differential conductance (NDC), verifying potential for low-power quantum applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optical Bandgap (Eg) | 1.0 | eV | Estimated from absorption onset (1,200 nm) |
| Local Charge Mobility (”local) | 450 ± 60 | cm2 V-1 s-1 | Ultrafast optical-pump terahertz-probe (OPTP) spectroscopy |
| DC Mobility (”dc limit) | 32 ± 4 | cm2 V-1 s-1 | Calculated, accounting for backscattering (cp = -0.93) |
| FET Field-Effect Mobility (Linear) | 40 ± 5 | cm2 V-1 s-1 | Room temperature, single-molecule FET |
| FET ION/IOFF Ratio | â 103 | N/A | Ambipolar FET operation at VSD = 0.1 V |
| Subthreshold Swing (SS) | 400 to 800 | mV dec-1 | Single-molecule FET switching performance |
| Average Chain Length (PGNRb) | 85 | nm | Deduced from GPC (N â 34 repeat units) |
| Weight-Average Molar Mass (Mw) | 132.7 | kDa | Polymer PPb, GPC analysis (Polystyrene standard) |
| PGNRb Width (WPGNR) | 1.1 | nm | Estimated from transport data |
| SET Lengths Detected | 10 ± 3 to 40 ± 3 | nm | Estimated from Coulomb diamonds addition energies (Eadd) |
| Terahertz Scattering Time (Ï) | 54 ± 7 | fs | Drude-Smith model fit |
| SET NDC Minimum Voltage | < 10 | mV | Minimum voltage of negative differential conductance regions |
Key Methodologies
Section titled âKey MethodologiesâThe synthesis and characterization relied on a two-step solution-phase approach followed by advanced spectroscopic and device measurements.
Synthesis (PGNRb)
Section titled âSynthesis (PGNRb)â- Monomer Selection: Dichloroporphyrin monomer 2b was used, featuring dodecyl chains on the meso-aryl groups and tert-butyl groups on the benzo[m]tetraphene core to enhance solubility and induce twisting. Ni(II) was pre-inserted into the porphyrin core.
- Polymerization (PPb): Yamamoto polymerization of monomer 2b was performed using Ni(COD)2 catalyst in Tetrahydrofuran (THF) solvent at 80 °C for 20 hours, yielding the precursor polymer PPb (93% yield).
- Planarization (PGNRb): Cyclodehydrogenation of PPb was achieved using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH) in dichloromethane (DCM) at 25 °C for 20 hours, yielding the final PGNRb (94% yield).
Characterization and Device Fabrication
Section titled âCharacterization and Device Fabricationâ- Molar Mass Determination: Gel Permeation Chromatography (GPC) and Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) mass spectrometry (linear mode, up to 210 kDa) were used to confirm high molecular weight and chain length.
- Structural Confirmation: Solid-state Cross-Polarization Magic-Angle Spinning (CP-MAS) 1H NMR and Raman/FT-IR spectroscopy confirmed the complete dehydrogenation and planarization of the PGNRb backbone.
- Imaging: Scanning Tunneling Microscopy (STM) of the precursor polymer PPa on Au(111) confirmed the chain-like structure and non-planarity, showing a repeating period of 1.8-2.5 nm.
- Charge Transport (Local): Ultrafast Optical-Pump Terahertz-Probe (OPTP) spectroscopy was used to measure contact-free charge mobility. A 400 nm optical pulse generated carriers, and a single-cycle terahertz pulse probed the transient photoconductivity.
- Device Fabrication: Single-nanoribbon devices were fabricated using electro-burnt graphene nanogaps (3-7 nm width) on a SiO2/Si substrate with a 10-nm-thick HfO2 dielectric layer for gate control.
- Electronic Measurement: Field-effect transistor (FET) characteristics were measured at room temperature. Single-electron transistor (SET) behavior, including Coulomb diamonds and NDC, was mapped at millikelvin temperatures (25 mK).
Commercial Applications
Section titled âCommercial ApplicationsâThe unique combination of high charge mobility, narrow bandgap, and engineerable magnetic centers makes PGNRs highly relevant for next-generation electronic and quantum technologies.
| Industry/Area | Application/Product Relevance | Key PGNR Feature Utilized |
|---|---|---|
| Molecular Electronics | High-performance, nanoscale field-effect transistors (FETs) and molecular wires. | High charge mobility (450 cm2 V-1 s-1) and ambipolar semiconductor character. |
| Spintronics & Quantum | Single-electron transistors (SETs), quantum memory, and magnetic switches. | Precise control over single-electron transport (Coulomb diamonds, NDC) and ability to incorporate magnetic metal ions (e.g., Fe, Mn) into the porphyrin core. |
| Infrared Optics | Photodetectors and sensors operating in the near-infrared (NIR) region. | Narrow optical bandgap (1.0 eV) corresponding to NIR absorption (up to 1,600 nm). |
| Advanced Materials | Creating novel GNR hybrids with engineerable electrical and magnetic properties. | Solution-phase scalability and the ability to transpose diverse coordination chemistry (porphyrin ligands) into the GNR backbone. |
| Low-Power Computing | Ultra-low power switching devices. | Observation of negative differential conductance (NDC) at very low bias (<10 mV), indicating potential for low-power operation. |