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Title: Porphyrin-based molecular triad systems for use in spin-entanglement and catalysis experiments
Author: Panjwani, Naitik Ashokkumar
ISNI:       0000 0004 7659 7624
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2018
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available