Structural Factors of Radical-Enhanced Intersystem Crossing of Organic Chromophores Open Access

Abstract

A long-lived triplet state is essential for various applications such as triplet-triplet annihilation upconversion, photodynamic therapy, and photocatalysis. Current research on efficiently generating long-lived triplet states mainly depends on the heavy atom effect, which limits the applications of triplet sensitizers in the biomedical field. Although triplet generation via radical enhanced intersystem crossing (EISC) of organic chromophores has been reported, discrepancies exist among different studies. In this project, we synthesized and measured the intersystem crossing (ISC) rate of boron dipyrromethene (BODIPY) with a 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical attached at different positions or with different distances. Anthracene (ACA)-TEMPO was also examined. The BODIPY results indicate a distance dependent radical EISC effect. The BODIPY-TEMPO molecule with a short rigid linker presented a higher ISC rate and a longer-lived triplet state, which was observed for the first time. The comparison between a short rigid and a long flexible linker revealed a through-bond effect of the radical EISC process. This work contributed to the finding of how radicals enhance intersystem crossing.

Table of Contents

Table of Content

List of Tables..................................................................................................................... 3

List of Schemes.................................................................................................................. 3

Chapter 1. Introduction................................................................................................... 1

1.1 Overview................................................................................................................... 1

1.2 Triplet State and Intersystem Crossing....................................................................... 2

1.3 BODIPY and Derivatives........................................................................................... 6

1.4 Anthracene and Derivatives....................................................................................... 7

1.5 Radical Enhanced Intersystem Crossing of Organic Chromophores......................... 8

Chapter 2. BODIPY-TEMPO System........................................................................... 11

2.1 Methods................................................................................................................... 11

2.1.1 Synthesis................................................................................................. 11

2.1.2 Steady State Absorbance and Fluorescence.......................................................... 13

2.1.3 Excited State Transient Spectroscopy Study...................................................... 14

2.2 Results and Discussion............................................................................................. 16

2.2.1 Synthesis and Characterization....................................................................................... 16

2.2.2 Steady State Analysis..................................................................................................................... 20

2.2.3 Excited State Analysis..................................................................................... 22

2.3 Conclusion............................................................................................................... 31

Chapter 3. Anthracene System...................................................................................... 33

3.1 Methods................................................................................................................... 33

3.1.1 Synthesis................................................................................................................. 33

3.1.2 Steady State Absorbance and Fluorescence..................................................................... 34

3.1.3 Excited State Transient Spectroscopy....................................................................... 35

3.2 Results...................................................................................................................... 35

3.2.1 Synthesis........................................................................................... 35

3.2.2 Absorbance................................................................................................. 41

3.2.3 Excited State Study............................................................................ 42

3.3 Conclusion............................................................................................................... 47

Appendix......................................................................................................................... 48

Bibliography.................................................................................................................. 50

About this Master's Thesis

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School	Laney Graduate School
Department	Chemistry
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Chemistry, Organic Chemistry, Physical
Keyword	Triplet state Radical Intersystem crossing
Committee Chair / Thesis Advisor	Lian, Tianquan, Emory University
Committee Members	Hill, Craig , Emory University Powell, Nichole, Oxford College at Emory University Evangelista, Francesco, Emory University

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