O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Observation of Ultrafast Charge Migration in an Amino Acid Louise Belshaw Queen’s University, Belfast

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Outline Observation of Ultrafast Charge Migration in an Amino Acid 1. Why biomolecules with attosecond lasers? 2. Phenylalanine 3. How: experimental pump – probe setup 4. Results with phenylalanine 5. Conclusions

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Ultrafast Dynamics in Biomolecules Ultrafast Dynamics: responsible for many important, fundamental processes in biomolecules, for example : excited energy redistribution in DNA: - strong UV absorption – excited state energy - ultrafast decay → prevents creation of harmful products charge transfer/migration – facilitates transmission of information -movement of electron hole across peptide backbone - ‘wires’ together distant atoms 1. Why biomolecules with attosecond lasers? F. Remacle and R.D. Levine PNAS 103, 6793 (2006). Why use ultrafast lasers? Short Pulses: femtoseconds, attoseconds (recently 67 as!) Time resolution: Observing the fastest processes in molecules Control

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Ultrafast Dynamics in Biomolecules 2.Phenylalanine Why? Chosen molecule: phenylalanine ‘Model’ for charge migration in biomolecular systems Two charge acceptor sites: Similar binding energy Separated by two singly bonded carbons Similar binding energy… If ΔE = 1 eV, T = 4 fs; If ΔE = 0.1 eV, T = 40 fs. ΔE = E 2 – E 1 f = ΔE / h T = h / ΔE Consider states 1, 2: ψ HOLE (t) = c 1 exp (-iE 1 t / ℏ ) + c 2 exp (-iE 2 / ℏ ) Then, hole charge density: │ψ HOLE (t)│ 2 = │c 1 │ 2 + │c 2 │ 2 + 2│c 1 c 2 *│cos(E 2 – E 1 )t / ℏ )

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW VIS/NIR from previous stages τ = 6fs, λ = nm Pump - Probe Set-Up in Politecnico di Milano Beamsplitter High Harmonic Generation

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Beamsplitter High Harmonic Generation XUV τ = 1.5 fs VIS/NIR Pulse Pump - Probe Set-Up in Politecnico di Milano VIS/NIR from previous stages τ = 6fs, λ = nm

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Beamsplitter VIS/NIR Pulse Delay Stage τ D Produce Gas Phase Sample VIS/NIR τ = 6 fs XUV τ = 1.5 fs Pump - Probe Set-Up in Politecnico di Milano High Harmonic Generation VIS/NIR from previous stages τ = 6fs, λ = nm

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Laser Induced Acoustic Desorption (LIAD) sample deposited on thin foil foil back irradiated neutral plume created studied in pump-probe scheme products extracted and analysed  produces neutral intact molecules  fs interaction with sample only (no matrix)  photo-sensitive molecules can be studied LIAD: Production of a Gas Phase Sample C.R. Calvert et al, Phys. Chem. Chem. Phys. 14, 6289 (2012).

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Laser Pulse Interaction with Phenylalanine Two laser pulses:1. XUV: eV, 1.5 fs 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs All outer shell electrons Plus Some inner shell electrons 1. XUV: eV, 1.5 fs Single Photon Ionisation How do these interact with phenylalanine?

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Laser Pulse Interaction with Phenylalanine Two laser pulses:1. XUV: eV, 1.5 fs 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs How do these interact with phenylalanine? 1. XUV: eV, 1.5 fs Single Photon Ionisation All outer shell electrons Plus Some inner shell electrons Fragmentation dependent upon location of charge in the molecule: charge in π 1 : include m/q = 65, 77, 91, 103 charge in n N : include m/q = 120, 74

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Laser Pulse Interaction with Phenylalanine Two laser pulses:1. XUV: eV, 1.5 fs 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs How do these interact with phenylalanine? 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs Multiphoton, Tunnelling Ionises from only the highest occupied molecular orbitals

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Laser Pulse Interaction with Phenylalanine Two laser pulses:1. XUV: eV, 1.5 fs 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs How do these interact with phenylalanine? 2. VIS/NIR: 1.3 – 2.5 eV, 6 fs Multiphoton, Tunnelling Only highest occupied molecular orbitals Mostly n N fragments Ionisation favoured from amine group

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Experiment in Phenylalanine Experimental Scheme Ionise first (pump) with XUV pulse Probe with VIS/NIR Follow the fragments’ yields as a function of the delay, τ D, between pump and probe. Figure: R. Weinkauf et al, J. Phys. Chem. 100, (1996). Probe with VIS/NIR Probing excitation in phenyl group (once charged, absorbs strongly in VIS) Probing charge on the amine group through ionisation

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Results in Phenylalanine Dynamics on the timescale τ = 80 fs Increase in yield for π 1 fragments Temporal dependence with changing delay between XUV and VIS/NIR pulses of a number of fragments in the spectra No time dependence in yield for n N fragments. Time delay, τ D Ion Yield Time delay, τ D Ion Yield L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012).

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Results in Phenylalanine Dynamics on the timescale τ = 80 fs Temporal dependence with changing delay between XUV and VIS/NIR pulses of a number of fragments in the spectra τ = 80 ± 20 fs Internal Conversion to the π 1 state following initial ionisation by XUV No absorption in neutral phenyl; Once charged, absorbs strongly in VIS. L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012). Increasing population in π 1 : opens up absorption by VIS/NIR. Increase in yield for π 1 fragments Time delay, τ D Ion Yield τ D < 0 τ D > 0

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Results in Phenylalanine Dynamics on the timescale τ = 30 fs Observed in the yield of the doubly charged immonium ion, m /q = 60 τ = 30 ± 5 fs L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012).

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW m/q = 60 Delay, τ D Pump – Probe Results in Phenylalanine m/q = 60 charge migration Dynamics on the timescale τ = 30 fs L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012). Probe with VIS/NIR Probing charge on the amine group through ionisation

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW m/q = 60 Delay, τ D Pump – Probe Results in Phenylalanine m/q = 60 charge migration Dynamics on the timescale τ = 30 fs τ = 30 fs consequence of the sensitivity of charge migration to nuclear rearrangement L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012).

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Conclusions We have identified two separate ultrafast processes in phenylalanine molecules: Attosecond pump pulses Few-cycle femtosecond probe pulses Double Ionisation technique powerful scheme for studying charge migration 80 ± 20 fs internal conversion 30 ± 5 fs charge migration

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Ultrafast Dynamics Research Dr. Jason Greenwood Prof. Ian Williams Martin Duffy Louise Belshaw Prof. Mauro Nisoli Dr. Francesca Calegari Andrea Trabattoni

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Results in Phenylalanine Dynamics on the timescale τ = 80 fs Temporal dependence with changing delay between XUV and VIS/NIR pulses of a number of fragments in the spectra τ = 80 ± 20 fs Internal Conversion to the π 1 state following initial ionisation by XUV Increases fragments due to charge on phenyl ring L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012). Probe with VIS/NIR Probing excitation in phenyl group (once charged, absorbs strongly in VIS) Increasing population in π 1 therefore opens up absorption by VIS/NIR pulse Increase in yield for π 1 fragments Time delay, τ D Ion Yield

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Pump – Probe Results in Phenylalanine Dynamics on the timescale τ = 80 fs Increase in yield for π 1 fragments Time delay, τ D Ion Yield Temporal dependence with changing delay between XUV and VIS/NIR pulses of a number of fragments in the spectra τ = 80 ± 20 fs Internal Conversion to the π 1 state following initial ionisation by XUV π 1 state absorbs strongly in VIS Increasing population in π 1 therefore opens up absorption by VIS/NIR pulse Increases fragments due to charge on phenyl ring L. Belshaw et al, J. Phys. Chem. Lett. 3, 3751 (2012).

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Experimental Results: Phenylalanine Single Pulse Studies: XUV, IR Mass spectra following irradiation of phe plumes with: (a) XUV, 1.5 fs pulses; (b) VIS/NIR, 6 fs pulses. Key fragments can be assigned as shown:

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Experimental Results: Phenylalanine Single Pulse Studies: XUV, IR Fragmentation dependent upon location of charge in the molecule: charge in π 1 : include m/q = 65, 77, 91, 103 charge in n N : include m/q = 120, 74

O BSERVATION OF ULTRAFAST CHARGE MIGRATION IN AN AMINO ACID SDG, Durham, January 2013 L OUISE B ELSHAW Experimental Results: Phenylalanine Single Pulse Studies: XUV, IR Note: XUV capable of ionising all outer and some inner shell electrons VIS/NIR capable only of ionising π 1 n N