Synthesis and Excited State Dynamics of Oligothiophene-Nitronyl Nitroxides Restricted; Files Only

Jin, Shijian (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/br86b4419?locale=en
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Abstract

Spin-electronics or spintronics are envisioned to have faster data processing and accessing capabilities and higher information storage density compared to traditional electronics due to their intrinsic spin properties. Currently, the field of spintronics is dominated by silicon-metal multilayer materials. Recently, organic-based materials, particularly pi-conjugated chromophores and persistent radicals, have been of interest due to their metal-like spin properties, photo-controllable spin states, structural flexibility, low-cost, and Eco-friendly manufacturing processibility. However, low charge carrier mobility, weak ferro-magnetism, and marginal understanding of the spin-dynamics in organic radicals have limited their applications. Oligothiophene-based radicals represent an attractive alternative and may potentially address these challenges because of the high carrier mobility observed in oligothiophenes (0.6 cm2V-1s-1). Furthermore, photoexcitation of oligothiophenes generate large population of long-living triplet state via intersystem crossing, where the spins are aligned, which infer potential ferromagnetic properties of oligothiophenes-radicals. This thesis presents and elaborates on the synthesis and spectroscopic studies of oligothiophene-nitronyl nitroxide (OT-NN) radicals. The crystal structure, packing pattern and steady-state magnetic properties of bithiophene-bis(nitronyl nitroxide) (1.4) are also studied. Electronic coupling as well as the presence of unpaired spins have completely changed the electronic structure. Computational and experimental approaches both prove that the existence of radical components in OTNN lower the bandgap through electronic coupling. Several new n-π* induced low-lying charge-transfer states are also present in the OTNN system. The possible post-photoexication spin transitions are analyzed using ultrafast transient absorption.


Table of Contents

1 Synthesis and Excited State Dynamics of Oligothiophene- Nitronyl Nitroxides 2

1.1 Introduction................................... 2

1.1.1 Spintronics............................... 2

1.1.2 Organic Radicals............................. 3

1.1.3 Oligo- and Poly-Thiophenes....................... 7

1.1.4 Oligothiophene-Radical.............................. 10

1.2 Experimental Methods............................. 13

1.2.1 General Procedure........................... 13

1.2.2 Synthesis................................. 15

1.3 Results and Discussion............................. 22

1.3.1 Synthesis................................. 22

1.3.2 Crystal Structure of 1.4......................... 26

1.3.3 EPR Spectra of 1.4............................ 28

1.3.4 Steady-State Absorption........................ 30

1.3.5 Steady-State Emission......................... 34

1.3.6 Excited-states Analysis........................ 37

1.3.7 Computation............................... 50

1.4 Conclusion.................................... 53

A Appendix........................................ 54

A.1 Appendix section................................. 54

Bibliography....................................... 57

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