Co-reporter:Reece Beekmeyer;Michael A. Parkes;Luke Ridgwell;Jamie W. Riley;Jiawen Chen;Ben L. Feringa;Andrew Kerridge
Chemical Science (2010-Present) 2017 vol. 8(Issue 9) pp:6141-6148
Publication Date(Web):2017/08/21
DOI:10.1039/C7SC01997A
Light-driven molecular motors derived from chiral overcrowded alkenes are an important class of compounds in which sequential photochemical and thermal rearrangements result in unidirectional rotation of one part of the molecule with respect to another. Here, we employ anion photoelectron spectroscopy to probe the electronic structure and dynamics of a unidirectional molecular rotary motor anion in the gas-phase and quantum chemistry calculations to guide the interpretation of our results. We find that following photoexcitation of the first electronically excited state, the molecule rotates around its axle and some population remains on the excited potential energy surface and some population undergoes internal conversion back to the electronic ground state. These observations are similar to those observed in time-resolved measurements of rotary molecular motors in solution. This work demonstrates the potential of anion photoelectron spectroscopy for studying the electronic structure and dynamics of molecular motors in the gas-phase, provides important benchmarks for theory and improves our fundamental understanding of light-activated molecular rotary motors, which can be used to inform the design of new photoactivated nanoscale devices.
Co-reporter:Joanne L. Woodhouse;Mariana Assmann;Michael A. Parkes;Helen Grounds;Steven J. Pacman;James C. Anderson;Graham A. Worth
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 34) pp:22711-22720
Publication Date(Web):2017/08/30
DOI:10.1039/C7CP04815G
The electronic structure and excited-state dynamics of the ubiquitous bioluminescent probe luciferin and its furthest red-shifted analogue infraluciferin have been investigated using photoelectron spectroscopy and quantum chemistry calculations. In our electrospray ionization source, the deprotonated anions are formed predominantly in their phenolate forms and are directly relevant to studies of luciferin and infraluciferin as models for their unstable oxyluciferin and oxyinfraluciferin emitters. Following photoexcitation in the range 357–230 nm, we find that internal conversion from high-lying excited states to the S1(1ππ*) state competes efficiently with electron detachment. In infraluciferin, we find that decarboxylation also competes with direct electron detachment and internal conversion. This detailed spectroscopic and computational study defines the electronic structure and electronic relaxation processes of luciferin and infraluciferin and will inform the design of new bioluminescent systems and applications.
Co-reporter:Oliver M. Kirkby, Michael A. Parkes, Simon P. Neville, Graham A. Worth, Helen H. Fielding
Chemical Physics Letters 2017 Volume 683(Volume 683) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.cplett.2017.04.035
•Combination of time-resolved photoelectron spectroscopy measurements and quantum dynamics calculations.•<50 fs relaxation on A1(1πσ∗) following photoexcitation at 249.5–240 nm.•<50 fs relaxation from B1(2ππ∗)-A2(π3pz)-B1(2πσ∗) (and A1(1πσ∗)) following photoexcitation at 200 nm.The non-radiative relaxation dynamics of pyrrole have been investigated using time-resolved photoelectron spectroscopy and quantum dynamics simulations. Following excitation of the A2(11πσ∗) state, we observe population flow out of the Franck-Condon region on a ≲50 fs timescale. Following excitation of the B2(21ππ∗) state, we observe population being transferred to the A2(11πσ∗) state on a <50 fs timescale and subsequently out of the Franck-Condon region, also on a <50 fs timescale. Quantum dynamics calculations suggest that population is transferred from the B2(21ππ∗) state through the A2(1π3pz) state to the B1(21πσ∗) state before being transferred to the A2(11πσ∗) state.Download high-res image (74KB)Download full-size image
Co-reporter:Alice Henley;Matus E. Diveky;Anand M. Patel;Michael A. Parkes;James C. Anderson
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 47) pp:31572-31580
Publication Date(Web):2017/12/06
DOI:10.1039/C7CP06950B
The photocycle of photoactive yellow protein (PYP) begins with small-scale torsional motions of the chromophore leading to large-scale movements of the protein scaffold triggering a biological response. The role of single-bond torsional molecular motions of the chromophore in the initial steps of the PYP photocycle are not fully understood. Here, we employ anion photoelectron spectroscopy measurements and quantum chemistry calculations to investigate the electronic relaxation dynamics following photoexcitation of four model chromophores, para-coumaric acid, its methyl ester, and two analogues with aliphatic bridges hindering torsional motions around the single bonds adjacent to the alkene group. Following direct photoexcitation of S1 at 400 nm, we find that both single bond rotations play a role in steering the PYP chromophore through the S1/S0 conical intersection but that rotation around the single bond between the alkene moiety and the phenoxide group is particularly important. Following photoexcitation of higher lying electronic states in the range 346–310 nm, we find that rotation around the single bond between the alkene and phenoxide groups also plays a key role in the electronic relaxation from higher lying states to the S1 state. These results have potential applications in tuning the photoresponse of photoactive proteins and materials with chromophores based on PYP.
Co-reporter:Conor McLaughlin;Mariana Assmann;Michael A. Parkes;Joanne L. Woodhouse;Ross Lewin;Helen C. Hailes;Graham A. Worth
Chemical Science (2010-Present) 2017 vol. 8(Issue 2) pp:1621-1630
Publication Date(Web):2017/01/30
DOI:10.1039/C6SC03833F
Green fluorescent protein (GFP) continues to play an important role in the biological and biochemical sciences as an efficient fluorescent probe and is also known to undergo light-induced redox transformations. Here, we employ photoelectron spectroscopy and quantum chemistry calculations to investigate how the phenoxide moiety controls the competition between electron emission and internal conversion in the isolated GFP chromophore anion, following photoexcitation with ultraviolet light in the range 400–230 nm. We find that moving the phenoxide group from the para position to the ortho position enhances internal conversion back to the ground electronic state but that adding an additional OH group to the para chromophore, at the ortho position, impedes internal conversion. Guided by quantum chemistry calculations, we interpret these observations in terms of torsions around the C–C–C bridge being enhanced by electrostatic repulsions or impeded by the formation of a hydrogen-bonded seven-membered ring. We also find that moving the phenoxide group from the para position to the ortho position reduces the energy required for detachment processes, whereas adding an additional OH group to the para chromophore at the ortho position increases the energy required for detachment processes. These results have potential applications in tuning light-induced redox processes of this biologically and technologically important fluorescent protein.
Co-reporter:Anastasia V. Bochenkova;Ciarán R. S. Mooney;Michael A. Parkes;Joanne L. Woodhouse;Lijuan Zhang;Ross Lewin;John M. Ward;Helen C. Hailes;Lars H. Andersen
Chemical Science (2010-Present) 2017 vol. 8(Issue 4) pp:3154-3163
Publication Date(Web):2017/03/28
DOI:10.1039/C6SC05529J
The Green Fluorescent Protein (GFP), which is widely used in bioimaging, is known to undergo light-induced redox transformations. Electron transfer is thought to occur resonantly through excited states of its chromophore; however, a detailed understanding of the electron gateway states of the chromophore is still missing. Here, we use photoelectron spectroscopy and high-level quantum chemistry calculations to show that following UV excitation, the ultrafast electron dynamics in the chromophore anion proceeds via an excited shape resonance strongly coupled to the open continuum. The impact of this state is found across the entire 355–315 nm excitation range, from above the first bound–bound transition to below the opening of higher-lying continua. By disentangling the electron dynamics in the photodetachment channels, we provide an important reference for the adiabatic position of the electron gateway state, which is located at 348 nm, and discover the source of the curiously large widths of the photoelectron spectra that have been reported in the literature. By introducing chemical modifications to the GFP chromophore, we show that the detachment threshold and the position of the gateway state, and hence the underlying excited-state dynamics, can be changed systematically. This enables a fine tuning of the intrinsic electron emission properties of the GFP chromophore and has significant implications for its function, suggesting that the biomimetic GFP chromophores are more stable to photooxidation.
Co-reporter:Jamie Tay, Michael A. Parkes, Kiri Addison, Yohan Chan, Lijuan Zhang, Helen C. Hailes, Philip C. Bulman Page, Stephen R. Meech, Lluís BlancafortHelen H. Fielding
The Journal of Physical Chemistry Letters 2017 Volume 8(Issue 4) pp:
Publication Date(Web):January 26, 2017
DOI:10.1021/acs.jpclett.7b00174
Kaede, an analogue of green fluorescent protein (GFP), is a green-to-red photoconvertible fluorescent protein used as an in vivo “optical highlighter” in bioimaging. The fluorescence quantum yield of the red Kaede protein is lower than that of GFP, suggesting that increasing the conjugation modifies the electronic relaxation pathway. Using a combination of anion photoelectron spectroscopy and electronic structure calculations, we find that the isolated red Kaede protein chromophore in the gas phase is deprotonated at the imidazole ring, unlike the GFP chromophore that is deprotonated at the phenol ring. We find evidence of an efficient electronic relaxation pathway from higher-lying electronically excited states to the S1 state of the red Kaede chromophore that is not accessible in the GFP chromophore. Rapid autodetachment from high-lying vibrational states of S1 is found to compete efficiently with internal conversion to the ground electronic state.
Co-reporter:Michael A. Parkes, Ciara Phillips, Michael J. Porter and Helen H. Fielding
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 15) pp:10329-10336
Publication Date(Web):24 Mar 2016
DOI:10.1039/C6CP00565A
Understanding how the interactions between a chromophore and its surrounding protein control the function of a photoactive protein remains a challenge. Here, we present the results of photoelectron spectroscopy measurements and quantum chemistry calculations aimed at investigating how substitution at the coumaryl tail of the photoactive yellow protein chromophore controls competing relaxation pathways following photoexcitation of isolated chromophores in the gas phase with ultraviolet light in the range 350–315 nm. The photoelectron spectra are dominated by electrons resulting from direct detachment and fast detachment from the 21ππ* state but also have a low electron kinetic energy component arising from autodetachment from lower lying electronically excited states or thermionic emission from the electronic ground state. We find that substituting the hydrogen atom of the carboxylic acid group with a methyl group lowers the threshold for electron detachment but has very little effect on the competition between the different relaxation pathways, whereas substituting with a thioester group raises the threshold for electron detachment and appears to ‘turn off’ the competing electron emission processes from lower lying electronically excited states. This has potential implications in terms of tuning the light-induced electron donor properties of photoactive yellow protein.
Co-reporter:Oliver M. Kirkby, Matthieu Sala, Garikoitz Balerdi, Rebeca de Nalda, Luis Bañares, Stéphane Guérin and Helen H. Fielding
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 25) pp:16270-16276
Publication Date(Web):14 May 2015
DOI:10.1039/C5CP01883H
Femtosecond time-resolved photoelectron spectroscopy experiments have been used to compare the electronic relaxation dynamics of aniline and d7-aniline following photoexcitation in the range 272–238 nm. Together with the results of recent theoretical investigations of the potential energy landscape [M. Sala, O. M. Kirkby, S. Guérin and H. H. Fielding, Phys. Chem. Chem. Phys., 2014, 16, 3122], these experiments allow us to resolve a number of unanswered questions surrounding the nonradiative relaxation mechanism. We find that tunnelling does not play a role in the electronic relaxation dynamics, which is surprising given that tunnelling plays an important role in the electronic relaxation of isoelectronic phenol and in pyrrole. We confirm the existence of two time constants associated with dynamics on the 11πσ* surface that we attribute to relaxation through a conical intersection between the 11πσ* and 11ππ* states and motion on the 11πσ* surface. We also present what we believe is the first report of an experimental signature of a 3-state conical intersection involving the 21ππ*, 11πσ* and 11ππ* states.
Co-reporter:Ciarán R. S. Mooney;Michael A. Parkes;Andreas Iskra
Angewandte Chemie International Edition 2015 Volume 54( Issue 19) pp:5646-5649
Publication Date(Web):
DOI:10.1002/anie.201500549
Abstract
To understand how photoactive proteins function, it is necessary to understand the photoresponse of the chromophore. Photoactive yellow protein (PYP) is a prototypical signaling protein. Blue light triggers trans–cis isomerization of the chromophore covalently bound within PYP as the first step in a photocycle that results in the host bacterium moving away from potentially harmful light. At higher energies, photoabsorption has the potential to create radicals and free electrons; however, this process is largely unexplored. Here, we use photoelectron spectroscopy and quantum chemistry calculations to show that the molecular structure and conformation of the isolated PYP chromophore can be exploited to control the competition between trans–cis isomerization and radical formation. We also find evidence to suggest that one of the roles of the protein is to impede radical formation in PYP by preventing torsional motion in the electronic ground state of the chromophore.
Co-reporter:Ciarán R. S. Mooney;Michael A. Parkes;Andreas Iskra
Angewandte Chemie 2015 Volume 127( Issue 19) pp:5738-5741
Publication Date(Web):
DOI:10.1002/ange.201500549
Abstract
To understand how photoactive proteins function, it is necessary to understand the photoresponse of the chromophore. Photoactive yellow protein (PYP) is a prototypical signaling protein. Blue light triggers trans–cis isomerization of the chromophore covalently bound within PYP as the first step in a photocycle that results in the host bacterium moving away from potentially harmful light. At higher energies, photoabsorption has the potential to create radicals and free electrons; however, this process is largely unexplored. Here, we use photoelectron spectroscopy and quantum chemistry calculations to show that the molecular structure and conformation of the isolated PYP chromophore can be exploited to control the competition between trans–cis isomerization and radical formation. We also find evidence to suggest that one of the roles of the protein is to impede radical formation in PYP by preventing torsional motion in the electronic ground state of the chromophore.
Co-reporter:Matthieu Sala, Oliver M. Kirkby, Stéphane Guérin and Helen H. Fielding
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 7) pp:3122-3133
Publication Date(Web):02 Jan 2014
DOI:10.1039/C3CP54418D
There have been a number of recent experimental investigations of the nonadiabatic relaxation dynamics of aniline following excitation to the first three singlet excited states, 11ππ*, 11π3s/πσ* and 21ππ*. Motivated by differences between the interpretations of experimental observations, we have employed CASSCF and XMCQDPT2 calculations to explore the potential energy landscape and relaxation pathways of photoexcited aniline. We find a new prefulvene-like MECI connecting the 11ππ* state with the GS in which the carbon-atom carrying the amino group is distorted out-of-plane. This suggests that excitation above the 11π3s/πσ* vertical excitation energy could be followed by electronic relaxation from the 11ππ* state to the ground-electronic state through this MECI. We find a MECI connecting the 11π3s/πσ* and 11ππ* states close to the local minimum on 11π3s/πσ* which suggests that photoexcitation to the 11π3s/πσ* state could be followed by relaxation to the 11ππ* state and to the dissociative component of the 11π3s/πσ* state. We also find evidence for a new pathway from the 21ππ* state to the ground electronic state that is likely to pass through a three-state conical intersection involving the 21ππ*, 11π3s/πσ* and 11ππ* states.
Co-reporter:Jason B. Greenwood, Jordan Miles, Simone De Camillis, Peter Mulholland, Lijuan Zhang, Michael A. Parkes, Helen C. Hailes, and Helen H. Fielding
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 20) pp:3588-3592
Publication Date(Web):October 3, 2014
DOI:10.1021/jz5019256
The photophysics of the green fluorescent protein is governed by the electronic structure of the chromophore at the heart of its β-barrel protein structure. We present the first two-color, resonance-enhanced, multiphoton ionization spectrum of the isolated neutral chromophore in vacuo with supporting electronic structure calculations. We find the absorption maximum to be 3.65 ± 0.05 eV (340 ± 5 nm), which is blue-shifted by 0.5 eV (55 nm) from the absorption maximum of the protein in its neutral form. Our results show that interactions between the chromophore and the protein have a significant influence on the electronic structure of the neutral chromophore during photoabsorption and provide a benchmark for the rational design of novel chromophores as fluorescent markers or photomanipulators.Keywords: absorption; femtosecond; gas phase; time-dependent density functional theory; ultraviolet;
Co-reporter:Ciarán R. S. Mooney
, Daniel A. Horke
, Adam S. Chatterley, Alexandra Simperler, Helen H. Fielding and Jan R. R. Verlet
Chemical Science 2013 vol. 4(Issue 3) pp:921-927
Publication Date(Web):26 Nov 2012
DOI:10.1039/C2SC21737F
The green fluorescent protein (GFP) is employed extensively as a marker in biology and the life sciences as a result of its spectacular fluorescence properties. Here, we employ femtosecond time-resolved photoelectron spectroscopy to investigate the ultrafast excited state dynamics of the isolated GFP chromophore anion. Excited state population is found to decay bi-exponentially, with characteristic lifetimes of 330 fs and 1.4 ps. Distinct photoelectron spectra can be assigned to each of these timescales and point to the presence of a transient intermediate along the decay coordinate. Guided by ab initio calculations, we assign these observations to twisting about the C–C–C bridge followed by internal conversion to the anion ground state. The dynamics in vacuo are very similar to those observed in solution, despite the difference in absorption spectra between the two media. This is consistent with the protein environment restricting rotation about the C–C–C bond in order to prevent ultrafast internal conversion and preserve the fluorescence.
Co-reporter:Roman Spesyvtsev, Oliver M. Kirkby, Morgane Vacher and Helen H. Fielding
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 28) pp:9942-9947
Publication Date(Web):08 Jun 2012
DOI:10.1039/C2CP41785E
Efficient electronic relaxation following the absorption of ultraviolet light is crucial for the photostability of biological chromophores, so understanding the microscopic details of the decay pathways is of considerable interest. Here, we employ femtosecond time-resolved photoelectron imaging to investigate the ultrafast intramolecular dynamics of aniline, a prototypical aromatic amine, following excitation just below the second absorption maximum. We find that both the second ππ* state and the Rydberg state are populated during the excitation process. Surprisingly, the dominant non-radiative decay pathway is an ultrafast relaxation mechanism that transfers population straight back to the electronic ground-state. The vibrational energy resolution and photoelectron angular distributions obtained in our experiments reveal an interesting bifurcation of the Rydberg population to two non-radiative decay channels. The existence of these competing non-radiative relaxation channels in aniline illustrates how its photostability arises from a subtle balance between dynamics on different electronically excited states and importantly between Rydberg and valence states.
Co-reporter:Ciarán R. S. Mooney, M. Eugenia Sanz, Adam R. McKay, Richard J. Fitzmaurice, Abil E. Aliev, Stephen Caddick, and Helen H. Fielding
The Journal of Physical Chemistry A 2012 Volume 116(Issue 30) pp:7943-7949
Publication Date(Web):June 27, 2012
DOI:10.1021/jp3058349
Isolated model anion chromophores of the green and cyan fluorescent proteins were generated in an electrospray ion source, and their photodetachment spectra were recorded using photoelectron imaging. Vertical photodetachment energies of 2.85(10) and 4.08(10) eV have been measured for the model green fluorescent protein chromophore anion, corresponding to photodetachment from the ground electronic state of the anion to the ground and first excited electronic states of the radical, respectively. For the model cyan fluorescent protein chromophore anion, vertical photodetachment energies of 2.88(10) and 3.96(10) eV have been measured, corresponding to detachment from the ground electronic state of the anion to the ground and first excited electronic states of the neutral radical, respectively. We also find evidence suggesting that autoionization of electronically excited states of the chromophore anions competes with direct photodetachment. For comparison and to benchmark our measurements, the vertical photodetachment energies of deprotonated phenol and indole anions have also been recorded and presented. Quantum chemistry calculations support our assignments. We discuss our results in the context of the isolated protein chromophore anions acting as electron donors, one of their potential biological functions.
Co-reporter:A. D. G. Nunn, R. S. Minns, R. Spesyvtsev, M. J. Bearpark, M. A. Robb and H. H. Fielding
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 48) pp:15751-15759
Publication Date(Web):10 Nov 2010
DOI:10.1039/C0CP01723J
We report a femtosecond time-resolved photoelectron spectroscopy (TRPES) investigation of internal conversion in the first two excited singlet electronic states of styrene. We find that radiationless decay through an S1/S0 conical intersection occurs on a timescale of ∼4 ps following direct excitation to S1 with 0.6 eV excess energy, but that the same process is significantly slower (∼20 ps) if it follows internal conversion from S2 to S1 after excitation to S2 with 0.3 eV excess energy (0.9 eV excess energy in S1).
Co-reporter:R. S. Minns, D. S. N. Parker, T. J. Penfold, G. A. Worth and H. H. Fielding
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 48) pp:15607-15615
Publication Date(Web):08 Jun 2010
DOI:10.1039/C001671C
We report new, detailed, femtosecond time-resolved photoelectron spectroscopy experiments and calculations investigating the competition between ultrafast internal conversion and ultrafast intersystem crossing in electronically and vibrationally excited benzene at the onset of “channel 3”. Using different probe energies to record the total photoelectron yield as a function of pump–probe delay we are able to confirm that S1, T1 and T2 electronic states are involved in the excited state dynamics. Time-resolved photoelectron spectroscopy measurements then allow us to unravel the evolution of the S1, T1 and T2 components of the excited state population and, together with complementary quantum chemistry and quantum dynamics calculations, support our earlier proposal that ultrafast intersystem crossing competes with internal conversion (Chem. Phys. Lett., 2009, 469, 43).
Co-reporter:D.S.N. Parker, R.S. Minns, T.J. Penfold, G.A. Worth, H.H. Fielding
Chemical Physics Letters 2009 Volume 469(1–3) pp:43-47
Publication Date(Web):3 February 2009
DOI:10.1016/j.cplett.2008.12.069
We investigate the ultrafast intramolecular dynamics of electronically and vibrationally excited benzene using time-resolved photoelectron spectroscopy and quantum dynamics simulations. In addition to an ultrafast initial decay, we observe an oscillation between two states. We interpret this data in terms of excited state population moving away from the Franck–Condon region towards the singlet–singlet conical intersection with the ground-state, where ultrafast intersystem crossing from the initially populated singlet state to an optically dark triplet state is enhanced. Our results challenge the currently accepted view that intramolecular processes in hydrocarbons which involve a change of spin are negligibly slow.Ultrafast radiationless decay from an excited singlet state of benzene to a triplet state (ultrafast intersystem crossing).
Co-reporter:R. E. Carley, E. Heesel and H. H. Fielding
Chemical Society Reviews 2005 vol. 34(Issue 11) pp:949-969
Publication Date(Web):29 Sep 2005
DOI:10.1039/B509463A
This critical review is intended to provide an overview of the state-of-the-art in femtosecond laser technology and recent applications in ultrafast gas phase chemical dynamics. Although “femtochemistry” is not a new subject, there have been some tremendous advances in experimental techniques during the last few years. Time-resolved photoelectron spectroscopy and ultrafast electron diffraction have enabled us to observe molecular dynamics through a wider window. Attosecond laser sources, which have so far only been exploited in atomic physics, have the potential to probe chemical dynamics on an even faster timescale and observe the motions of electrons. Huge progress in pulse shaping and pulse characterisation methodology is paving the way for exciting new advances in the field of coherent control. (203 references.)
Co-reporter:Roman Spesyvtsev, Oliver M. Kirkby, Morgane Vacher and Helen H. Fielding
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 28) pp:NaN9947-9947
Publication Date(Web):2012/06/08
DOI:10.1039/C2CP41785E
Efficient electronic relaxation following the absorption of ultraviolet light is crucial for the photostability of biological chromophores, so understanding the microscopic details of the decay pathways is of considerable interest. Here, we employ femtosecond time-resolved photoelectron imaging to investigate the ultrafast intramolecular dynamics of aniline, a prototypical aromatic amine, following excitation just below the second absorption maximum. We find that both the second ππ* state and the Rydberg state are populated during the excitation process. Surprisingly, the dominant non-radiative decay pathway is an ultrafast relaxation mechanism that transfers population straight back to the electronic ground-state. The vibrational energy resolution and photoelectron angular distributions obtained in our experiments reveal an interesting bifurcation of the Rydberg population to two non-radiative decay channels. The existence of these competing non-radiative relaxation channels in aniline illustrates how its photostability arises from a subtle balance between dynamics on different electronically excited states and importantly between Rydberg and valence states.
Co-reporter:R. S. Minns, D. S. N. Parker, T. J. Penfold, G. A. Worth and H. H. Fielding
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 48) pp:NaN15615-15615
Publication Date(Web):2010/06/08
DOI:10.1039/C001671C
We report new, detailed, femtosecond time-resolved photoelectron spectroscopy experiments and calculations investigating the competition between ultrafast internal conversion and ultrafast intersystem crossing in electronically and vibrationally excited benzene at the onset of “channel 3”. Using different probe energies to record the total photoelectron yield as a function of pump–probe delay we are able to confirm that S1, T1 and T2 electronic states are involved in the excited state dynamics. Time-resolved photoelectron spectroscopy measurements then allow us to unravel the evolution of the S1, T1 and T2 components of the excited state population and, together with complementary quantum chemistry and quantum dynamics calculations, support our earlier proposal that ultrafast intersystem crossing competes with internal conversion (Chem. Phys. Lett., 2009, 469, 43).
Co-reporter:A. D. G. Nunn, R. S. Minns, R. Spesyvtsev, M. J. Bearpark, M. A. Robb and H. H. Fielding
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 48) pp:NaN15759-15759
Publication Date(Web):2010/11/10
DOI:10.1039/C0CP01723J
We report a femtosecond time-resolved photoelectron spectroscopy (TRPES) investigation of internal conversion in the first two excited singlet electronic states of styrene. We find that radiationless decay through an S1/S0 conical intersection occurs on a timescale of ∼4 ps following direct excitation to S1 with 0.6 eV excess energy, but that the same process is significantly slower (∼20 ps) if it follows internal conversion from S2 to S1 after excitation to S2 with 0.3 eV excess energy (0.9 eV excess energy in S1).
Co-reporter:Ciarán R. S. Mooney
, Daniel A. Horke
, Adam S. Chatterley, Alexandra Simperler, Helen H. Fielding and Jan R. R. Verlet
Chemical Science (2010-Present) 2013 - vol. 4(Issue 3) pp:NaN927-927
Publication Date(Web):2012/11/26
DOI:10.1039/C2SC21737F
The green fluorescent protein (GFP) is employed extensively as a marker in biology and the life sciences as a result of its spectacular fluorescence properties. Here, we employ femtosecond time-resolved photoelectron spectroscopy to investigate the ultrafast excited state dynamics of the isolated GFP chromophore anion. Excited state population is found to decay bi-exponentially, with characteristic lifetimes of 330 fs and 1.4 ps. Distinct photoelectron spectra can be assigned to each of these timescales and point to the presence of a transient intermediate along the decay coordinate. Guided by ab initio calculations, we assign these observations to twisting about the C–C–C bridge followed by internal conversion to the anion ground state. The dynamics in vacuo are very similar to those observed in solution, despite the difference in absorption spectra between the two media. This is consistent with the protein environment restricting rotation about the C–C–C bond in order to prevent ultrafast internal conversion and preserve the fluorescence.
Co-reporter:Anastasia V. Bochenkova, Ciarán R. S. Mooney, Michael A. Parkes, Joanne L. Woodhouse, Lijuan Zhang, Ross Lewin, John M. Ward, Helen C. Hailes, Lars H. Andersen and Helen H. Fielding
Chemical Science (2010-Present) 2017 - vol. 8(Issue 4) pp:
Publication Date(Web):
DOI:10.1039/C6SC05529J
Co-reporter:Conor McLaughlin;Mariana Assmann;Michael A. Parkes;Joanne L. Woodhouse;Ross Lewin;Helen C. Hailes;Graham A. Worth
Chemical Science (2010-Present) 2017 - vol. 8(Issue 2) pp:
Publication Date(Web):2017/01/30
DOI:10.1039/C6SC03833F
Green fluorescent protein (GFP) continues to play an important role in the biological and biochemical sciences as an efficient fluorescent probe and is also known to undergo light-induced redox transformations. Here, we employ photoelectron spectroscopy and quantum chemistry calculations to investigate how the phenoxide moiety controls the competition between electron emission and internal conversion in the isolated GFP chromophore anion, following photoexcitation with ultraviolet light in the range 400–230 nm. We find that moving the phenoxide group from the para position to the ortho position enhances internal conversion back to the ground electronic state but that adding an additional OH group to the para chromophore, at the ortho position, impedes internal conversion. Guided by quantum chemistry calculations, we interpret these observations in terms of torsions around the C–C–C bridge being enhanced by electrostatic repulsions or impeded by the formation of a hydrogen-bonded seven-membered ring. We also find that moving the phenoxide group from the para position to the ortho position reduces the energy required for detachment processes, whereas adding an additional OH group to the para chromophore at the ortho position increases the energy required for detachment processes. These results have potential applications in tuning light-induced redox processes of this biologically and technologically important fluorescent protein.
Co-reporter:Michael A. Parkes, Ciara Phillips, Michael J. Porter and Helen H. Fielding
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 15) pp:NaN10336-10336
Publication Date(Web):2016/03/24
DOI:10.1039/C6CP00565A
Understanding how the interactions between a chromophore and its surrounding protein control the function of a photoactive protein remains a challenge. Here, we present the results of photoelectron spectroscopy measurements and quantum chemistry calculations aimed at investigating how substitution at the coumaryl tail of the photoactive yellow protein chromophore controls competing relaxation pathways following photoexcitation of isolated chromophores in the gas phase with ultraviolet light in the range 350–315 nm. The photoelectron spectra are dominated by electrons resulting from direct detachment and fast detachment from the 21ππ* state but also have a low electron kinetic energy component arising from autodetachment from lower lying electronically excited states or thermionic emission from the electronic ground state. We find that substituting the hydrogen atom of the carboxylic acid group with a methyl group lowers the threshold for electron detachment but has very little effect on the competition between the different relaxation pathways, whereas substituting with a thioester group raises the threshold for electron detachment and appears to ‘turn off’ the competing electron emission processes from lower lying electronically excited states. This has potential implications in terms of tuning the light-induced electron donor properties of photoactive yellow protein.
Co-reporter:Matthieu Sala, Oliver M. Kirkby, Stéphane Guérin and Helen H. Fielding
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 7) pp:
Publication Date(Web):
DOI:10.1039/C3CP54418D
Co-reporter:Oliver M. Kirkby, Matthieu Sala, Garikoitz Balerdi, Rebeca de Nalda, Luis Bañares, Stéphane Guérin and Helen H. Fielding
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 25) pp:NaN16276-16276
Publication Date(Web):2015/05/14
DOI:10.1039/C5CP01883H
Femtosecond time-resolved photoelectron spectroscopy experiments have been used to compare the electronic relaxation dynamics of aniline and d7-aniline following photoexcitation in the range 272–238 nm. Together with the results of recent theoretical investigations of the potential energy landscape [M. Sala, O. M. Kirkby, S. Guérin and H. H. Fielding, Phys. Chem. Chem. Phys., 2014, 16, 3122], these experiments allow us to resolve a number of unanswered questions surrounding the nonradiative relaxation mechanism. We find that tunnelling does not play a role in the electronic relaxation dynamics, which is surprising given that tunnelling plays an important role in the electronic relaxation of isoelectronic phenol and in pyrrole. We confirm the existence of two time constants associated with dynamics on the 11πσ* surface that we attribute to relaxation through a conical intersection between the 11πσ* and 11ππ* states and motion on the 11πσ* surface. We also present what we believe is the first report of an experimental signature of a 3-state conical intersection involving the 21ππ*, 11πσ* and 11ππ* states.
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