Gatto, Marco Filippo
(2025)
Single-Molecular Electronic Studies on an Open-Shell Diindolocarbazole Derivative and d10 Organophosphorous Complexes.
PhD thesis, University of Liverpool.
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Abstract
The pressing technological challenges that traditional electronics is facing, driven primarily by the physical limitations of Moore’s law, have spurred scientific research to explore new avenues for developing advanced electronic devices. Molecular electronics, although conceptually proposed in the early 1950s, is emerging as a promising solution by providing atomic and molecular-scale alternatives to conventional electronic components. One of the key areas of focus in molecular electronics is the implementation and optimization of electronic transport across single-molecular junctions. This research often utilizes scanning probe techniques, such as Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM), or other sophisticated instruments, to probe molecular electronic conductance at the atomic level. The primary aim of this thesis is to examine and compare how open-shell molecules and certain d10 transition metal complexes can influence electron transport when used as molecular bridges between two gold electrodes in a STM setup. To achieve this goal, the closed-shell molecule N,N–bis(4-methylthiophenyl)indolo[3,2-b]carbazole (MSP-ICz) was synthesized and thoroughly characterized. The effect of its open-shell configuration, obtained by in situ oxidation, on electronic conductance was explored using a combination of traditional and electrochemical gated STM-Break Junction (STM-BJ) techniques. Titration of MSP-ICz by trifluoroacetic acid (TFA) demonstrated a significant improvement in the electronic transport upon chemical oxidation, with the neutral compound (MSP-ICz) conductance being on the order of 10-5 G0, compared to a notable enhancement to values greater than 10-4 G0 for the radical cation. This finding underscores the importance of open-shell molecular junctions in advancing molecular electronics, though further investigation into the isolated oxidized species and its characteristics remains ongoing. Notably, electrochemically gated STM-BJ studies confirmed the above results and revealed that the chemical equilibrium between the neutral and radical species is voltage-dependent, highlighting the potential for dynamic control of this equilibrium and its molecular junction conductance. The second major focus of this thesis is the study of transition metals in molecular junctions, specifically exploring how different metal centres may influence the electronic properties of molecular junctions. Initial investigations were conducted using mononuclear organometallic cations of copper, silver, and gold, all in their +1 oxidation state, and bis-chelated by N,N–bis(diphenylphosphino)-4-methylthioaniline (MeS-DPPAn). While stability of these complexes in the presence of gold nanoparticles was confirmed by Raman and Surface-Enhanced Raman Scattering (SERS) spectroscopies, STM-BJ measurements at applied biases of 300 mV and 500 mV revealed that the choice of metal centre did not significantly affect the molecular junction conductance, which remained at approximately 10-5 G0. Pursuing the idea that both the geometry and number of metal centres may affect the electronic conductance of a molecular junction; this thesis ends up with some attempts of synthesis and characterization of multi-nuclear organometallic compounds of copper (I) and silver (I). The [Cu2(µ2-MeSDPPAn)2(MeCN)x][PF6] (x = 0, 2, or 4) was synthesized but not successfully crystallized due to its lability. The trinuclear copper (I) complex [Cu3(η3-CCPy)2(µ2 – DPPM)3][PF6] (DPPM = bis(diphenylphosphino)methane) was isolated for exploring even the effect of the 5 centres – 4 electrons configuration on the single-molecular conductance. Unfortunately, due to the lability of the cluster, the molecular junction broke up while measuring the conductance, resulting in a 10-3 – 10-2 G0 with small electrode separation corresponding to the acetylide fragment. The silver (I) analogous was synthesized but still under investigation. Other tri-nuclear copper (I) [Cu3(µ2 – MeS-DPPAn)3(η3 – X)2]X (X = Cl, Br and I) as well as tetranuclear analogous clusters have been considered for the purposes of this thesis and still under ongoing investigation.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering Faculty of Science and Engineering > School of Physical Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 21 Aug 2025 08:25 |
| Last Modified: | 21 Aug 2025 08:26 |
| DOI: | 10.17638/03190755 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3190755 |
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