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Porphyrin-based molecular triad systems for use in spin-entanglement and catalysis experiments

Panjwani, Naitik Ashokkumar; (2018) Porphyrin-based molecular triad systems for use in spin-entanglement and catalysis experiments. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Here we study a set of porphyrin-based molecular triad systems for the purpose of using the long-lived charge separated state (CCS), 1) as a tool to hyperpolarise, entangle and measure nuclear spins in molecules and 2) to spin-catalyse molecular hydrogen encapsulated in a fullerene cage as part of a porphyrin-C_60 system. In light of the above goals, we firstly study a series of triad systems where the moieties of each system are chosen so as to increase the driving force for electron transfer and obtain a system where the CSS is long-lived (on the order of a few tens of milliseconds). We study the porphyrin-based systems using a combination of theoretical, electrochemical and electron paramagnetic resonance (EPR) studies, to quantitatively understand the charge and spin dynamics. We find that from a series of three triad systems (TAPD-MP_Ar-C_60 where M = Zn, H_2 and Cd) the longest-lived CSS2 is obtained on the zinc porphyrin triad, 32 ms at 10 K — due to slow T_1 relaxation. The singlet recombination lifetime is 11 µs in xylenes and 3 µs in 2MeTHF, at cryogenic temperatures. The highest quantum yield is obtained from the cadmium porphyrin triad, around 0.15. Magneto-photo-selection experiments along with EPR simulations are used to derive mechanistic detail about energy migration in the triad systems after photo-excitation, while Liouville space simulations are used to extract spin Hamiltonian parameters for the SCRP. We detect ortho-H_2 using ENDOR and NMR before attempting to use the CSS as a spin-catalyst for H_2. In the final chapter we use optical pump-probe spectroscopy to monitor the charge migration at room temperature where we find the lifetime of the CSS_2 to be around 8 – 10 ns. We also present a new electric field resonator design for carrying out microwave dielectric absorption experiments.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Porphyrin-based molecular triad systems for use in spin-entanglement and catalysis experiments
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2018. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) Licence (https://creativecommons.org/licenses/by-nc-sa/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: electron paramagnetic resonance, porphyrin, C60, triplet states, spin correlated radical pair, magneto-photo-selection, electron transfer, energy transfer, quantum information, spin dynamics, ortho-hydrogen, para-hydrogen, transient absorption spectroscopy, NMR, microwave dielectric absorption.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10062747
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