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  6. Prof. Ludovic Troian-Gautier
  7. Research overview

Research overview

MOST

Our research is distributed among several axis:

  • Understanding factors governing excited state reactivity and charge separation.
  • Light-induced solar fuels production (H2 production, CO2 reduction, HX and H2O splitting)
  • Mechanistic photoredox catalysis using rare and earth abundant transition metal complexes and organic dyes.

Our independent research is also made possible through very fruitful collaborations:

 

Ongoing international collaborations:

  • Renato Sampaio, University of North Carolina at Chapel Hill (UNC), USA
  • Alejandro Cadranel, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany, and Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina
  • Uttam Tambar, Biochemsitry department, UT Southwestern, USA

 

Ongoing national collaborations:

  • Benjamin Elias, UCLouvain, Institut de la Matière Condensée et des Nanosciences
  • Ivan Jabin, ULB, Laboratoire de Chimie Organique.
  • Emilie Cauët, ULB, Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing SQUARES

 

  • Understanding factors governing excited state reactivity and charge separation.

The use of light to promote chemical reactions has been of scientific interest since the early 1900’s. To mimic natural processes, scientists have designed compounds, better known as photosensitizers (PS), that harvest radiant energy to promote, or sensitize, given reactions. Light activation of the photosensitizers triggers the formation of an excited state that follows a reaction pathway broadly depicted in figure 1.

 

Figure 1. Photophysical scheme for oxidative electron transfer between a photosensitizer (PS) and a quencher (Q).

 

In solution, the excited photosensitizer (PS*) diffuses towards the quencher (Q), that can either be an electron donor or acceptor, forming a so-called “encounter complex”. If thermodynamically favorable, the electron transfer event can occur, generating the corresponding geminate pair of radicals (oxidized and reduced species), either {PS•–;Q•+} or {PS•+;Q•–}. These species can either recombine to regenerate the initial state or undergo cage-escape to generate the charge-separated products that can be further used to drive targeted applications, i.e. photoredox catalysis in solution, solar fuel formation and photochemotherapy.

We are able to investigate most of these excited-state processes via steady-state an time-resolved spectroscopy available within the laboratory.

 

Selected publications related to the project (click on the title to access the editor’s website):

  1. A. Aydogan, R. E. Bangle, A. Cadranel, M. D. Turlington, E. Cauët, M. Singleton, G. J. Meyer,* R. N. Sampaio,* B. Elias,* L. Troian-Gautier,* Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light, J. Am. Chem. Soc., 2021, 143, 15661-15673.
  1. A. Aydogan, R. E. Bangle, S. De Kreiger, J. C. Dickenson, M. L. Singleton, E. Cauët, A. Cadranel, G. J. Meyer, B. Elias*, R. N. Sampaio,* L. Troian-Gautier* Mechanistic Investigation of a Visible Light Mediated Dehalogenation/Cyclisation Reaction using Iron(III), Iridium(III) and Ruthenium(II) Photosensitizers, Catal. Sci. Technol., 2021, 11, 8037-8051 (Invited for “Emerging Investigators” Series”)
  1. A. Cotic, L. Slep, S. Cerfontaine, B. Elias, L. Troian-Gautier,* A. Cadranel,* A Photoinduced Mixed Valence Photoswitch, Phys. Chem. Chem. Phys., 2022, 24, 15121-15128.
  1. A. M. Deetz, L. Troian-Gautier, S. A. M. Wehlin, E. J. Piechota, G. J. Meyer*, On the Determination of Halogen Atom Reduction Potentials with Photoredox Catalysts, J. Phys. Chem. A, 2021, 125, 9355-9367

 

  • Light-induced solar fuels production (H2 production, CO2 reduction, HX and H2O splitting)

The necessity for new sources of energy and feedstock is currently at its greatest. The sun, that provides us with roughly 50 terawatts of energy per year, has long been viewed as a promising candidate for a renewable energy source. This amount of energy, if collected in its entirety, is several times greater than the amount of energy currently consumed annually. Photovoltaic technologies have been shown to be very efficient for solar energy conversion to electricity but, due to the diurnal cycle, storing this energy has become a key challenge. One way by which this energy source can be “stored” is in chemical bonds of small and highly energetic molecules such as molecular hydrogen (H2) or oxygen (O2) through various chemical transformations. Proposed means of generating solar fuels are hydrohalic (HX, X = I, Br, Cl) oxidation and water (H2O) oxidation, in which O2 and H2 are produced upon light irradiation concomitant with either H+ or X2.

This process can be seen as an efficient energy storage nanotechnology, as it uses light to oxidize readily available H2O/HX, whose molecular component X2 or O2 and H2 can be easily stored and recombined in a fuel cell upon increased energy demand. The H2O oxidation process is thus a critical reaction that requires highly energetic photoredox reactions, but which is already exploited in nature (see oxygen evolving complex of Photosystem II). In contrast, the hydrohalic photooxidation requires even higher energy. Therefore, catalysts with high oxidation power are of utmost importance and highly desirable.

To reach these ambitious goals, we are developing new photoactivatable nanostructured materials and new photosensitizers competent to drive the challenging reactions.

 

Selected publications related to the project (click on the title to access the editor’s website)::

  1. R. Bevernaegie, S. A. M. Wehlin, E. J. Piechota, M. Abraham, C. Philouze, G. J. Meyer, B. Elias*, L. Troian-Gautier*, Improved Visible Light Absorption of Potent Iridium(III) Photooxidants for Excited-State Electron Transfer Chemistry, J. Am. Chem. Soc., 2020, 142, 2732-2737.
  1. M. Wodon, S. De Kreijger, R. Sampaio, B. Elias,* L. Troian-Gautier* Accumulation of Mono-Reduced [Ir(piq)2(LL)] Photosensitizers Relevant for Solar Fuels Production, Photochem. Phototobiol. Sci., 2022, 21, 1433-1444.
  1. L. Troian-Gautier, M. D. Turlington, S. A. M. Wehlin, A. M. Maurer, M. D. Brady, W. B. Swords, G. J. Meyer*, Halide Photoredox Chemistry, Chem. Rev., 2019, 119, 4628-4683.
  1. S. De Kreijger, O. Schott, L. Troian-Gautier, E. Cauët, G. S. Hanan, B. Elias,* Red absorbing cyclometalated Ir(III) diimine photosensitizers competent for hydrogen photo-evolution, Inorg. Chem., 2022, 61, 5245-5254
  1. J. Zhao, S. De Kreijger, L. Troian-Gautier, J Yu, W Hu, X Zhang, B. Elias*, D. Moonshiram*, Deciphering the Photophysical Kinetics, Electronic Configurations and Structural Conformations of Iridium-Cobalt Hydrogen Evolution Potocatalysts, Chem. Commun., 2022, 58, 8057-8060.
  1. S. A. M. Wehlin,# L. Troian-Gautier,# A. B. Maurer, M. K. Brennaman, G. J. Meyer, Photophysical Characterization of New Osmium (II) Photocatalysts for Hydrohalic Acid Splitting, J. Chem. Phys., 2020, 153, 054307.
  1. D. Wang#, R. N. Sampaio#, L. Troian-Gautier, S. L. Marquard, B. H. Farnum, C. J. Dares, G. J. Meyer, T. J. Meyer*, A Molecular Photoelectrode for Water Oxidation Inspired by Photosystem II, J. Am. Chem. Soc., 2019, 141, 7926–7933.

 

  • Mechanistic photoredox catalysis using rare and earth abundant transition metal complexes and organic dyes.

Photoredox catalysis is a booming filed that relies on the premise that photosensitizers (or photocatalysts) are inactive in the dark, but exhibit a drastic shift in their redox potential upon photon absorption. These shift in excited-state reduction potentials can be experimentally estimated using common steady-state techniques available in the laboratory. Alternatively, the excited-state photosensitizer can undergo energy transfer (and not electron transfer), leading to activation of organic substrate with conservation of spin multiplicity.

Our approach relies on the use of steady-state and time-resolved spectroscopic techniques, coupled to electrochemistry to investigate excited-state reactivity. For example, with the Tambar (UT Southwestern) and Gutierrez (University of Maryland) groups, we have developed a novel light-induced cyclopropanation approach that proceeds via an underexplored energy transfer mechanism. With the Elias group (UCLouvain), we developed polynuclear Ru(II) complexes (up to quadrinuclear) that were shown to be more stable, produce higher reaction yields, and work with lower energy wavelengths than their mononuclear analogues. We also recently used an iron(III) complex for visible light dehalogenation reactions. We have determined key parameters that allowed to achieve efficient excited-state electron transfer with large cage-escape yields using green light irradiation. Dehalogenation reactions operated with large yields and a clear view of the mechanistic pathway with the associated rate constants was obtained by a combination of time-resolved spectroscopic methods, such as femtosecond and nanosecond transient absorption or infrared spectroscopy (TRIR).

 

Selected publications related to the project (click on the title to access the editor’s website)::

  1. A. Aydogan, R. E. Bangle, A. Cadranel, M. D. Turlington, E. Cauët, M. Singleton, G. J. Meyer,* R. N. Sampaio,* B. Elias,* L. Troian-Gautier,* Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light, J. Am. Chem. Soc., 2021, 143, 15661-15673.
  1. A. Aydogan, R. E. Bangle, S. De Kreiger, J. C. Dickenson, M. L. Singleton, E. Cauët, A. Cadranel, G. J. Meyer, B. Elias*, R. N. Sampaio,* L. Troian-Gautier* Mechanistic Investigation of a Visible Light Mediated Dehalogenation/Cyclisation Reaction using Iron(III), Iridium(III) and Ruthenium(II) Photosensitizers, Catal. Sci. Technol., 2021, 11, 8037-8051 (Invited for “Emerging Investigators” Series”)
  1. S. Cerfontaine, S. A. M. Wehlin, B. Elias*, L. Troian-Gautier,* Photostable Polynuclear Ruthenium (II) Photosensitizers Competent for Dehalogenation Photoredox Catalysis at 590 nm, J. Am. Chem. Soc., 2020, 142, 5549-5555.
  1. B. Xu, L. Troian-Gautier,* R. Dykstra, R. Martin, O. Gutierrez,* U. K. Tambar*, Photocatalyzed Diastereoselective Isomerization of Cinnamyl Chlorides to Cyclopropanes, J. Am. Chem. Soc., 2020, 142, 6206-6215.