Phase Tag-Assisted Synthesis of Benzo[<i>b</i>]carbazole End-Capped Oligothiophenes

The introduction and removal of a phase tag have been used to trigger cyclization events in a new synthesis of benzo[<i>b</i>]carbazoles. The approach has been exploited in a tag-assisted approach to new benzo[<i>b</i>]carbazole end-capped oligothiophenes for preliminary evaluation as semiconductors

A Sm(II)-Mediated Cascade Approach to Dibenzoindolo[3,2‑<i>b</i>]carbazoles: Synthesis and Evaluation

Previously unstudied dibenzoindolo­[3,2-<i>b</i>]­carbazoles have been prepared by two-directional, phase tag-assisted synthesis utilizing a connective-Pummerer cyclization and a SmI₂-mediated tag cleavage–cyclization cascade. The use of a phase tag allows us to exploit unstable intermediates that would otherwise need to be avoided. The novel materials were characterized by X-ray, cyclic voltammetry, UV–vis spectroscopy, TGA, and DSC. Preliminary studies on the performance of OFET devices are also described

A Sm(II)-Mediated Cascade Approach to Dibenzoindolo[3,2‑<i>b</i>]carbazoles: Synthesis and Evaluation

Previously unstudied dibenzoindolo­[3,2-<i>b</i>]­carbazoles have been prepared by two-directional, phase tag-assisted synthesis utilizing a connective-Pummerer cyclization and a SmI₂-mediated tag cleavage–cyclization cascade. The use of a phase tag allows us to exploit unstable intermediates that would otherwise need to be avoided. The novel materials were characterized by X-ray, cyclic voltammetry, UV–vis spectroscopy, TGA, and DSC. Preliminary studies on the performance of OFET devices are also described

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution

We report a combined experimental and theoretical investigation of the length dependence and anchor group dependence of the electrical conductance of a series of oligoyne molecular wires in single-molecule junctions with gold contacts. Experimentally, we focus on the synthesis and properties of diaryloligoynes with <i>n</i> = 1, 2, and 4 triple bonds and the anchor dihydrobenzo­[<i>b</i>]­thiophene (BT). For comparison, we also explored the aurophilic anchor group cyano (CN), amino (NH₂), thiol (SH), and 4-pyridyl (PY). Scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics. The BT moiety is superior as compared to traditional anchoring groups investigated so far. BT-terminated oligoynes display a 100% probability of junction formation and possess conductance values which are the highest of the oligoynes studied and, moreover, are higher than other conjugated molecular wires of similar length. Density functional theory (DFT)-based calculations are reported for oligoynes with <i>n</i> = 1–4 triple bonds. Complete conductance traces and conductance distributions are computed for each family of molecules. The sliding of the anchor groups leads to oscillations in both the electrical conductance and the binding energies of the studied molecular wires. In agreement with experimental results, BT-terminated oligoynes are predicted to have a high electrical conductance. The experimental attenuation constants β_H range between 1.7 nm^–1 (CN) and 3.2 nm^–1 (SH) and show the following trend: β_H(CN) < β_H(NH₂) < β_H(BT) < β_H(PY) ≈ β_H(SH). DFT-based calculations yield lower values, which range between 0.4 nm^–1 (CN) and 2.2 nm^–1 (PY)

Single-Molecule Conductance Behavior of Molecular Bundles

Controlling the orientation of complex molecules in molecular junctions is crucial to their development into functional devices. To date, this has been achieved through the use of multipodal compounds (i.e., containing more than two anchoring groups), resulting in the formation of tri/tetrapodal compounds. While such compounds have greatly improved orientation control, this comes at the cost of lower surface coverage. In this study, we examine an alternative approach for generating multimodal compounds by binding multiple independent molecular wires together through metal coordination to form a molecular bundle. This was achieved by coordinating iron(II) and cobalt(II) to 5,5′-bis(methylthio)-2,2′-bipyridine (L1) and (methylenebis(4,1-phenylene))bis(1-(5-(methylthio)pyridin-2-yl)methanimine) (L2) to give two monometallic complexes, Fe-1 and Co-1, and two bimetallic helicates, Fe-2 and Co-2. Using XPS, all of the complexes were shown to bind to a gold surface in a fac fashion through three thiomethyl groups. Using single-molecule conductance and DFT calculations, each of the ligands was shown to conduct as an independent wire with no impact from the rest of the complex. These results suggest that this is a useful approach for controlling the geometry of junction formation without altering the conductance behavior of the individual molecular wires