Design and Application of Heavy Atom-Free and Redox-Active Organic Triplet Photosensitizers
Lead Research Organisation:
CARDIFF UNIVERSITY
Department Name: Chemistry
Abstract
Visible-light assisted chemical transformation has come forward as a powerful mode of small-molecule activation in conjunction with the recent quest for sustainable chemistry. The popularity of inorganic photosensitizers in this field stems from the long lifetime and strong redox power in their easily formed triplet excited states. However, triplet formation from metal-free, photo-redox organic materials is often regarded as an inefficient process, leading these compounds to receive little attention from relevant applications. Since the established organic synthetic methodologies should provide a well-tailored reactivity in organic redox photosensitizers, in this project, we want to challenge the conventional believes and provide a general method to enable the photosensitizing capability in organic molecules.
We aim to achieve the following three objectives. (1) We will expand the current toolbox of photosensitizer/photocatalyst by exploiting the underutilized thiocarbonyl photochemistry to generate energetic, long-lived triplet excited state of organic chromophores for efficient electron transfer reactions with a complete understanding of their excited state dynamics. (2) We will understand the factors controlling the triplet energy, lifetime, and chemical stability of thiocarbonyl chromophores and to develop methods to tailor these features. And (3) we will discover other novel methods or mechanisms for heavy atom-free organic redox photosensitizer/photocatalyst based on the knowledge acquired in this project. Phase 1 of the project will focus mostly on chromophore discovery, which will be assisted by quantum chemical calculations. With a few triplet chromophores identified, in Phase 2, the research will focus on property tuning, which is essential to address two important aspects for these chromophores to be useful: (i) The molecules should exhibit excellent photo and chemical stability upon irradiation under reaction conditions. (ii) Secondly, to achieve good selectivity toward specific reactions, the electronic structure of the triplet chromophores should be tailored accordingly. We will fulfill these requirements by molecular substituent effects, conformation control, and supramolecular interactions. Our effort will be concentrated on catalytic processes that can be accomplished by one-electron transfer. In addition to the context of photo-redox catalysis, it is important to point out that the triplet-enhancing strategy that we will develop will be general to be applicable to a broad range of research where long-lived excited state and/or triplet state is of interest. For instance, in organic photovoltaics, enabling the triplet channel of photo-active, high performing molecules/polymers would enhancing charge separation quantum yields due to longer exciton lifetime or the formation of triplet radical ion pairs that recombines slowly due to spin restriction.
We aim to achieve the following three objectives. (1) We will expand the current toolbox of photosensitizer/photocatalyst by exploiting the underutilized thiocarbonyl photochemistry to generate energetic, long-lived triplet excited state of organic chromophores for efficient electron transfer reactions with a complete understanding of their excited state dynamics. (2) We will understand the factors controlling the triplet energy, lifetime, and chemical stability of thiocarbonyl chromophores and to develop methods to tailor these features. And (3) we will discover other novel methods or mechanisms for heavy atom-free organic redox photosensitizer/photocatalyst based on the knowledge acquired in this project. Phase 1 of the project will focus mostly on chromophore discovery, which will be assisted by quantum chemical calculations. With a few triplet chromophores identified, in Phase 2, the research will focus on property tuning, which is essential to address two important aspects for these chromophores to be useful: (i) The molecules should exhibit excellent photo and chemical stability upon irradiation under reaction conditions. (ii) Secondly, to achieve good selectivity toward specific reactions, the electronic structure of the triplet chromophores should be tailored accordingly. We will fulfill these requirements by molecular substituent effects, conformation control, and supramolecular interactions. Our effort will be concentrated on catalytic processes that can be accomplished by one-electron transfer. In addition to the context of photo-redox catalysis, it is important to point out that the triplet-enhancing strategy that we will develop will be general to be applicable to a broad range of research where long-lived excited state and/or triplet state is of interest. For instance, in organic photovoltaics, enabling the triplet channel of photo-active, high performing molecules/polymers would enhancing charge separation quantum yields due to longer exciton lifetime or the formation of triplet radical ion pairs that recombines slowly due to spin restriction.
Organisations
People |
ORCID iD |
| Anna Wright (Student) |
Publications
Wright A
(2021)
Triplet-Forming Thionated Donor-Acceptor Chromophores for Electrochemically Amphoteric Photosensitization
in European Journal of Organic Chemistry
| Description | Chemical applications such as solar power, LEDs, MRI imaging, cell imaging, photodynamic therapy and singlet fission often relies on inorganic photosensitisers, where inorganic materials are known to be expensive and unsustainable. This award has allowed for the development of a new molecular design of competitive sustainable organic photosensitisers. We have done this by utilising a donor-acceptor structure and the encorporation of varied equivalents carbonyl/thiocarbonyl functional groups. We have applied these materials as photocatalysts, demonstrating their possible use in industrial applications too. Our proposed design will soon be applied to a new range of compounds in order to test our hypothesis and create materials with broader applications. Additionally, modification of our first class of molecules will help us to understand the importance of each internal moiety and how they are required for photosensitisation to occur. In addition we have also discovered a series of compounds that exhibit solid-state emission. The origin of emission will be studied in order to see if these materials could be applied in OLEDs or solid-state lasers, where this area of photochemistry is poorly understood we hope to provide an insight into the photophyisical properties. |
| Exploitation Route | A universal design for organic photosensitisation has not previously been developed, with our proposed design we have been able to demonstrate reproducible photosensitisation across a range of organic molecules. Future studies will include transient absorption studies and EPR studies in order to underpin the origin of photosensitisation; this would not be limited to the organic molecules created in this award, but also the scope of the molecular design on other common dye molecules that have been classically used in inorganic chromophores in order to achieve photosensitisation. Additionally the creation of devices to understand the real world applications could lead to some interesting molecules for LEDs, solar cells, photodynamic therapy reagents etc. |
| Sectors | Chemicals Electronics Energy Manufacturing including Industrial Biotechology Pharmaceuticals and Medical Biotechnology |