Mapping Pathways in Photo-Catalytic Cycles using Ultrafast Spectroscopy
Lead Research Organisation:
University of Bristol
Department Name: Chemistry
Abstract
Catalysts are widely used in reactions which produce chemicals for a variety of everyday applications including pharmaceuticals and advanced materials such as polymers. They enhance the rates at which the products form, and their use can avoid harsh process conditions such as high temperatures. Photocatalysts that are activated by visible light are attracting attention because cheap light sources such as light emitting diodes (LEDs) can be used to drive useful chemical reactions. There is also growing interest in replacing photocatalysts containing transition metals with more sustainable organic compounds. Despite the recent and rapid development of photocatalytic cycles tailored to carry out specific chemical transformations, relatively little effort has been devoted to understanding the ways in which the photocatalysts work (their mechanisms of action) and the properties of the photocatalysts which should be optimized for greater efficiency. The proposed research will make detailed observations of the reactive species involved in catalytic cycles and their lifetimes, and in favourable cases will aim to observe every step in a full catalytic cycle from its initiation to its termination by recovery of the catalyst in its starting form.
The timescales for production and removal of the reactive intermediates are short, typically corresponding to femtosecond to picosecond intervals (less than one billionth of a second). The ultrafast lasers to be used in this research are capable of generating pulses of ultraviolet and infrared light short enough to take snapshots of the changing concentrations of these transient species. Consequently, the individual steps in a sequence of chemical reactions can be observed in a single set of measurements. Ultraviolet spectra are particularly informative about activated intermediates in excited electronic states, whereas infrared spectra provide specific information about the different molecules and radicals present at any particular time.
These unprecedented studies will use two ultrafast lasers, one located at the University of Bristol and the other at the Rutherford Appleton Laboratory (RAL). The Bristol laser will act as the workhorse system, profiling reaction intermediates and studying reactions up to times of 1.3 nanoseconds from initiation. The most interesting systems will then be studied using a laser system at RAL which has the unique capability to observe reactions over 11 orders of magnitude of time (from 100 femtoseconds to 10 milliseconds) in single sets of measurements. With this remarkable capability, we will capture every step in a photocatalytic cycle from start to finish for the first time. The rates at which each step occurs can then be interpreted to determine which properties of the photocatalyst, reactive substrate and surrounding solvent are most important for determining the efficiency of the reaction. Armed with new insights of this type, we will design novel photocatalytic cycles for important chemical reactions, such as those that form new bonds between carbon atoms (an essential structural feature of organic molecules), and test their performance using the methods adopted by organic chemists.
The benefits will be widespread. Organic chemists designing more efficient pathways to chosen target molecules, for example for medicinal applications, will have an extended palette of reactions at their disposal. This greater chemical control will also open up new classes of molecule that can be synthesized. The chemical and pharmaceutical industries rely on chemical synthesis to create new products such as drugs or advanced materials with properties tailored precisely to specific applications. They will draw upon the knowledge gained to refine existing industrial processes, and will also improve their understanding of how to develop new processes by activation of flowing samples of chemicals by illumination with cheap light sources.
The timescales for production and removal of the reactive intermediates are short, typically corresponding to femtosecond to picosecond intervals (less than one billionth of a second). The ultrafast lasers to be used in this research are capable of generating pulses of ultraviolet and infrared light short enough to take snapshots of the changing concentrations of these transient species. Consequently, the individual steps in a sequence of chemical reactions can be observed in a single set of measurements. Ultraviolet spectra are particularly informative about activated intermediates in excited electronic states, whereas infrared spectra provide specific information about the different molecules and radicals present at any particular time.
These unprecedented studies will use two ultrafast lasers, one located at the University of Bristol and the other at the Rutherford Appleton Laboratory (RAL). The Bristol laser will act as the workhorse system, profiling reaction intermediates and studying reactions up to times of 1.3 nanoseconds from initiation. The most interesting systems will then be studied using a laser system at RAL which has the unique capability to observe reactions over 11 orders of magnitude of time (from 100 femtoseconds to 10 milliseconds) in single sets of measurements. With this remarkable capability, we will capture every step in a photocatalytic cycle from start to finish for the first time. The rates at which each step occurs can then be interpreted to determine which properties of the photocatalyst, reactive substrate and surrounding solvent are most important for determining the efficiency of the reaction. Armed with new insights of this type, we will design novel photocatalytic cycles for important chemical reactions, such as those that form new bonds between carbon atoms (an essential structural feature of organic molecules), and test their performance using the methods adopted by organic chemists.
The benefits will be widespread. Organic chemists designing more efficient pathways to chosen target molecules, for example for medicinal applications, will have an extended palette of reactions at their disposal. This greater chemical control will also open up new classes of molecule that can be synthesized. The chemical and pharmaceutical industries rely on chemical synthesis to create new products such as drugs or advanced materials with properties tailored precisely to specific applications. They will draw upon the knowledge gained to refine existing industrial processes, and will also improve their understanding of how to develop new processes by activation of flowing samples of chemicals by illumination with cheap light sources.
Planned Impact
Beyond the academic beneficiaries summarized above, we anticipate significant consequences of our research for the UK chemical and pharmaceuticals industries. These benefits will primarily derive from deeper mechanistic understanding of photocatalysed reactions leading to improved processes for preparation of fine chemicals and pharmaceuticals over a range of production scales, for example using photochemical flow reactors with sustainable organic photocatalysts. The new chemical procedures developed may also offer access to new or challenging chemical spaces, allowing wider exploration of applications of novel compounds. The longer term aspiration is that the fundamental research described here will have benefits to the economy and to society, the former through more efficient and sustainable industrial processes and the latter through consequent enhancements of health and quality of life.
The research will lead directly to highly trained and employable personnel, with skills spanning synthetic chemistry and compound characterization, catalysis, transient ultra-violet/visible and infra-red spectroscopy, use of lasers, quantitative spectroscopic data analysis, kinetic modelling, electronic structure calculations, and communication of results. Although the postdoctoral researchers appointed to the project will each develop a subset of these skills for their primary roles, we expect cross fertilization, as well as complementary training of postgraduate students joining the project through the Bristol Chemical Synthesis Centre for Doctoral Training. Dissemination of the research outcomes to the wider synthetic organic chemistry community will introduce new methods for the study of reaction mechanisms to this active field of research.
A substantial effort will be made to communicate the principles of the research (photocatalysis, sustainable chemistry, applications of spectroscopy) to non-specialist audiences such as school-age children through development of outreach activities and materials. This communication of our research will therefore benefit those studying chemistry at pre-university level, other interested groups, and the researchers who will train in, and contribute to, these science communication actions.
The research will lead directly to highly trained and employable personnel, with skills spanning synthetic chemistry and compound characterization, catalysis, transient ultra-violet/visible and infra-red spectroscopy, use of lasers, quantitative spectroscopic data analysis, kinetic modelling, electronic structure calculations, and communication of results. Although the postdoctoral researchers appointed to the project will each develop a subset of these skills for their primary roles, we expect cross fertilization, as well as complementary training of postgraduate students joining the project through the Bristol Chemical Synthesis Centre for Doctoral Training. Dissemination of the research outcomes to the wider synthetic organic chemistry community will introduce new methods for the study of reaction mechanisms to this active field of research.
A substantial effort will be made to communicate the principles of the research (photocatalysis, sustainable chemistry, applications of spectroscopy) to non-specialist audiences such as school-age children through development of outreach activities and materials. This communication of our research will therefore benefit those studying chemistry at pre-university level, other interested groups, and the researchers who will train in, and contribute to, these science communication actions.
Publications
Bhattacherjee A
(2021)
Singlet and Triplet Contributions to the Excited-State Activities of Dihydrophenazine, Phenoxazine, and Phenothiazine Organocatalysts Used in Atom Transfer Radical Polymerization.
in Journal of the American Chemical Society
Bhattacherjee A
(2019)
Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights.
in Nature communications
Lewis-Borrell L
(2020)
Mapping the multi-step mechanism of a photoredox catalyzed atom-transfer radical polymerization reaction by direct observation of the reactive intermediates.
in Chemical science
Lewis-Borrell L
(2021)
Direct Observation of Reactive Intermediates by Time-Resolved Spectroscopy Unravels the Mechanism of a Radical-Induced 1,2-Metalate Rearrangement.
in Journal of the American Chemical Society
Orr-Ewing AJ
(2019)
Perspective: How can ultrafast laser spectroscopy inform the design of new organic photoredox catalysts for chemical and materials synthesis?
in Structural dynamics (Melville, N.Y.)
Robertson PA
(2021)
Tuning the Excited-State Dynamics of Acetophenone Using Metal Ions in Solution.
in The journal of physical chemistry letters
Silvi M
(2019)
Radical Addition to Strained s-Bonds Enables the Stereocontrolled Synthesis of Cyclobutyl Boronic Esters.
in Journal of the American Chemical Society
Sneha M
(2021)
Structure-Dependent Electron Transfer Rates for Dihydrophenazine, Phenoxazine, and Phenothiazine Photoredox Catalysts Employed in Atom Transfer Radical Polymerization
in The Journal of Physical Chemistry B
Sneha M
(2023)
Photoredox-HAT Catalysis for Primary Amine a-C-H Alkylation: Mechanistic Insight with Transient Absorption Spectroscopy.
in ACS catalysis
Sneha M
(2020)
Solvent-dependent photochemical dynamics of a phenoxazine-based photoredox catalyst
in Zeitschrift für Physikalische Chemie
Venkatraman RK
(2021)
Solvent Effects on Ultrafast Photochemical Pathways.
in Accounts of chemical research
Description | Extensive studies have been undertaken of the properties of a range of organic photocatalysts based on phenazine, phenoxazine and phenothiazine core structures. These catalysts are currently being employed by other groups worldwide for controlled synthesis of high quality polymers. However, their mechanisms of operation are poorly understood, which limits the design of improved molecular architectures to trial-and-error approaches. The recent measurements of excited state lifetimes and electron transfer rates for several structurally distinct photocatalyst molecules, and the study of the influence of different solvents, provides quantitative data on which to build robust design principles for future photocatalysts. The multi-step mechanisms of light-activated radical chain reactions of importance in organic synthesis have been tracked from start to finish for the first time by observing all the short-lived reactive intermediates. These measurements use time-resolved infra-red absorption spectroscopy and span 8 orders of magnitude of time to give unprecedented insights about complex chemical pathways. |
Exploitation Route | The design principles we are developing will inform the next generations of organic photoredox catalysts for a wide range of chemical and materials synthesis applications. We are working now with research groups interested in design of organic photocatalysts. |
Sectors | Chemicals Pharmaceuticals and Medical Biotechnology |
Description | The findings form this research have so far led to the following impact: Syngenta iCASE studentship award, with Dr Alex Cresswell (University of Bath): "A holistic approach to understanding & optimizing photocatalytic reactions". Preliminary discussions with Astra Zeneca about the use of photoredox catalysed chemistry in their medicinal chemistry and process divisions. Developing contacts with further potential industrial partners through a new EPSRC Centre for Doctoral Training in Photoinduced Processes in Molecules and Materials which I was invited to co-lead with colleagues from University College London on the basis of my EPSRC-funded research. Collaboration with Prof Mon Sang Kwon of Seoul National University which may lead to further industrial partnerships. |
First Year Of Impact | 2021 |
Sector | Chemicals,Pharmaceuticals and Medical Biotechnology |
Impact Types | Economic |
Description | Ultrafast Photochemical Dynamics in Complex Environments |
Amount | £8,055,185 (GBP) |
Funding ID | EP/V026690/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 08/2021 |
End | 08/2027 |
Title | Observation of photoredox catalytic cycles over 10 orders of magnitude of time |
Description | The LIFEtime laser facility at the Rutherford Appleton Laboratory has been applied for the first time to study multiple, sequential steps in photo-induced catalytic cycles on timescales from 100 fs to 1 ms. The measurements use transient infra-red absorption spectroscopy to monitor the production and loss of reactive intermediates over a previously inaccessible range of timescales. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2018 |
Provided To Others? | Yes |
Impact | Improved design of organic molecules for use in photoredox catalysis for synthesis of specialist chemicals and materials (e.g. polymers). |
Title | Acetophenone Ultrafast Photodynamics in Solution |
Description | Effects of dissolved metal ions on the ultrafast, non-adiabatic photochemical pathways in acetophenone. Data are from transient ultrafast absorption spectroscopy measurements. |
Type Of Material | Database/Collection of data |
Year Produced | 2021 |
Provided To Others? | Yes |
Impact | Understanding of how metal ion coordination affects ultrafast photochemical processes in solution. |
URL | https://data.bris.ac.uk/data/dataset/xh2zv1gyw3t32artke2sqbyr9/ |
Title | Amine alkylation photoredox catalysis |
Description | Transient absorption spectroscopy of a photoredox catalytic cycle using 4CzIPN and azide anions for hydrogen atom abstraction to activate primary amines. |
Type Of Material | Database/Collection of data |
Year Produced | 2023 |
Provided To Others? | Yes |
Impact | New insights into an important class of reactions. |
URL | https://data.bris.ac.uk/data/dataset/10lppiug4bgdk2nljkbto8qm73/ |
Title | BCB Boronate Transient Absorption Spectroscopy |
Description | Time-resolved spectra of reactive intermediates in a radical induced 1,2-metallate rearrangement reaction involving a bicylcobutyl boronate, and steady state spectra of reagents. |
Type Of Material | Database/Collection of data |
Year Produced | 2021 |
Provided To Others? | Yes |
Impact | Direct observation of the intermediate species over the full duration of a catalytic cycle, allowing precise determination of the reaction mechanism and kinetics. |
URL | https://data.bris.ac.uk/data/dataset/1rqqqklh0weug2vdhpllu5561p/ |
Title | Organic photoredox catalytic cycle for PCBN |
Description | Experimental data associated with the ERC Advanced Grant project CAPRI (PI Prof A.J. Orr-Ewing) and from use of the Central Laser Facility at the Rutherford Appleton Laboratory. |
Type Of Material | Database/Collection of data |
Year Produced | 2020 |
Provided To Others? | Yes |
URL | https://data.bris.ac.uk/data/dataset/1bbuxza4dih8f2r16p114vozuo/ |
Title | Ultrafast Chemical Dynamics: Photocatalytic decarboxylation |
Description | Experimental data associated with the ERC Advanced Grant project CAPRI (PI Prof A.J. Orr-Ewing) and from use of the Central Laser Facility at the Rutherford Appleton Laboratory. Time resolved spectroscopy data for intermediates in a photocatalytic decarboxylation cycle using phenanthrene, dicyanobenzene and cyclohexane carboxylic acid |
Type Of Material | Database/Collection of data |
Year Produced | 2019 |
Provided To Others? | Yes |
Description | iCASE Award with University of Bath and Syngenta |
Organisation | Syngenta International AG |
Department | Syngenta Ltd (Bracknell) |
Country | United Kingdom |
Sector | Private |
PI Contribution | A new collaboration with Dr Alex Cresswell (University of Bath) on photoredox reaction mechanisms has led to a successful application led by Dr Cresswell for an iCASE studentship supported by Syngenta. The project will start in Sept 2020. |
Collaborator Contribution | Dr Alex Cresswell (University of Bath) is contributing synthetic chemistry expertise. Syngenta is supporting a 4-year iCASE student and consumables. |
Impact | No outputs yet. |
Start Year | 2020 |
Description | iCASE Award with University of Bath and Syngenta |
Organisation | University of Bath |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | A new collaboration with Dr Alex Cresswell (University of Bath) on photoredox reaction mechanisms has led to a successful application led by Dr Cresswell for an iCASE studentship supported by Syngenta. The project will start in Sept 2020. |
Collaborator Contribution | Dr Alex Cresswell (University of Bath) is contributing synthetic chemistry expertise. Syngenta is supporting a 4-year iCASE student and consumables. |
Impact | No outputs yet. |
Start Year | 2020 |
Description | Schools outreach by Tim Harrison |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | Schools outreach based on research conducted in the School of Chemistry, University of Bristol. |
Year(s) Of Engagement Activity | 2019,2020,2021,2022 |
URL | http://www.chemlabs.bris.ac.uk/outreach/ |