Mapping Light-induced Chemical Dynamics in Organic Rings ...

Photochemistry:

Ring opening;

Bond dissociation etc.

Photophysics:

Intersystem crossing,

Spin crossover etc.

Time / seconds 10-15 10-12 10-6 10-3

S1

S0

T1

T2

S2

Aditi Bhattacherjee Marie Curie Fellow

AMOLF, The Netherlands

Photobiology:

Enzyme action, Radical polymerization,

Photocatalytic Reaction, etc.

Mapping Light-induced Chemical Dynamics

in Organic Rings from Ultrafast to Ultraslow

Organic Rings

Carbon Catenation Functional Matter:

Charge transfer requires heteroatoms

Heterocyclic Rings

Porphyrins

Nucleobases

Natural

Products

Carbon chains

Carbon rings

Ring Opening

Ring opening

Vitamin-D synthesis in skin in the presence

of sunlight

Biological significance Technological significance

7-dehydrocholesterol

Changes color in the presence of light

Spiropyran

Ashfold et al., JPCL (Perspective) 8, 3440, 2017

Kortekaas et al., ChemSocRev, 48, 3406, 2019

Anderson et al., JPCA, 103, 10730, 1999

Fuss et al., JPC, 100, 921, 1996

Time / seconds 10-15 10-12 10-6 10-3

Breaking and Making of Chemical Bonds

S1

S0

T1

T2

S2

A A* hν

(Excited state) (Ground state)

B A A* A* + X Y A*

(triplet)

(singlet)

Complex Reactions:



Photochemistry:

Ring opening; Isomerization;


Photophysics:


Spin crossover etc.

Time / seconds 10-15 10-12 10-6 10-3

Breaking and Making of Chemical Bonds

S1

S0

T1

T2

S2

A A* hν


B A A* A* + X Y A*

(triplet)

(singlet)

Photochemistry:



Photophysics:


Spin crossover etc.

Complex Reactions:



Time / seconds 10-15 10-12 10-6 10-3

Evolving Electronic and Nuclear Structures

S1

S0

T1

T2

S2

A A* hν


B A A* A* + X Y A*

(triplet)

(singlet)

Vitam

in D

synth

esis

,

Vis

ion

Photo

redox C

ata

lysis

Poly

mer

Synth

esis

/

Mole

cula

r re

cognitio

n

Photochemistry:



Photophysics:


Spin crossover etc.

Complex Reactions:



Chemical Reactivity and Bonding

in Small Organic Molecules

The Periodic Table of Elements

s orbital

s block

p orbitals

p block

Chemical Bonding

Combining Atomic Orbitals to form Molecular Orbitals

Linear Combination Overlap and Mixing

φ1, φ2

𝟏

√𝟐 (φ1 + φ2)

𝟏

√𝟐 (φ1 - φ2)

σ

σ*

Energ

y

Chemical Bonding

Linear Combination Overlap and Mixing

φ1, φ2

𝟏

√𝟐 (φ1 + φ2)

𝟏

√𝟐 (φ1 - φ2)

Energ

y

Combining Atomic Orbitals to form Molecular Orbitals

π

π*

“Visualizing” Chemical Reactions: Connecting Electronic Energy with Nuclear Motion

+

Internuclear Distance (Bond length)

“Visualizing” Chemical Reactions: Connecting Electronic Energy with Nuclear Motion

π2

ππ*

πσ*

Internuclear Distance (Bond length)

Chemistry of Excited Electronic States

Peak-to-peak energy separation

• Easy bond activation

• Clean, targeted chemical reactions

(often, not always!)

• Central to photosynthesis, photoredox

catalysis, photoelectrochemistry etc.

Energ

y

Reaction coordinate

Time-resolved electronic (X-ray) absorption spectroscopy

Reaction coordinate

Methodology

Attar, Bhattacherjee and Leone

JPhysChemLett. 6, 5072, 2015

(Editors’ Choice)

Bhattacherjee, Attar and Leone

JChemPhys 144, 124311, 2016

(Editors’ Choice)

Pump-Probe Spectroscopy

Attar, Bhattacherjee, Das, Schnorr,

Closser, Prendergast, and Leone

Science 356, 54, 2017

Bhattacherjee, Das, Schnorr, Attar

and Leone

JAmChemSoc 139, 46, 2017

4.66 eV (266 nm)

30-300 eV (40-4 nm)

Reaction coordinate Reaction coordinate

Pote

ntial energ

y

Pote

ntial energ

y

Probing Photochemical Reactions with an X-ray pulse

via Excitation of Core Electrons

Potential Energy Curves

Optical

X-ray

Ultrafast Photochemistry:



Non-adiabatic Photophysics:


Spin crossover etc.

Time / seconds 10-15 10-12 10-6 10-3

Evolving Electronic and Nuclear Structures

S1

S0

T1

T2

S2

Fs X-ray Transient

Absorption Spectroscopy

Bimolecular Reactions:



Ionization Continuum

X − Y

NEXAFS

EXAFS

Near-Edge X-ray Absorption Fine Structure

Extended X-ray Absorption Fine Structure

Typical X-ray Absorption Spectrum

Energ

y→

NEXAFS Spectroscopy, Stohr (Springer 1996)

Valence

σ, π orbitals

σ*, π* orbitals

Core 1s, 2s, 2p, etc.

1. Element Specific

Advantages of using X-ray Probe

NEXAFS Spectroscopy, Stohr (Springer 1996)

Photon energy/eV

Inte

nsity

2. Orbital Specific


Carbon K-edge Nitrogen K-edge

Carbon Nitride

Thomas et al., J. Mater. Chem., 18, 4893, 2008 Photon energy/eV

Inte

nsity

3. Chemical Site Specific 1s→π* core-to-valence resonance

Photon energy/eV

Inte

nsity

Baldea et al., J. Elec. Spec. and Rel. Phen., 154, 109, 2007


Tabletop X-rays: 30-320 eV, 35-70 fs

I Br Si P S Cl C Be B

Stephen R.

Leone

Andrew

Attar

Kirsten

Schnorr

Zheyue

(Marina) Yang

Tian

(Chris) Xue

University of California, Berkeley

Lawrence Berkeley National Laboratory 1) Broadband

2) Energy-Tunable 3) Multiple Absorption Edges

Photon energy / eV

Bhattacherjee and Leone AccChemRes 21, 3203, 2018

Photochemical Reactions Studied

A-BAND PHOTODISSOCIATION OF HALOGENATED ALKANES

PERICYCLIC RING OPENING IN 1,3-CYCLOHEXADIENE

HETEROCYCLIC RING OPENING IN FURFURAL

ULTRAFAST INTERSYSTEM CROSSING IN ACETYLACETONE

BOND-SELECTIVE PHOTODISSOCIATION IN DIMETHYLDISULFIDE

Science 356, 6333, 2017

JACS 139, 46, 2017

JPCL 13, 82, 2019

JACS 140, 12538, 2018

JPCL 6, 24, 2015 (Editors’ Choice); JCP 144, 12, 2016 (Editors’ Choice); JACS 140, 41, 13360, 2018

Ultrafast Ring Opening:1,3-Cyclohexadiene

1A

1B 2A

Potential energy surface

Reaction co-ordinate

En

erg

y

cZc, HT tZt, HT

Pericyclic

Minimum

tZc, HT CHD

Electronic Structure

2A 1B

1A

1A(HT)

Theoretical X-ray Spectra

1B

1A

2A

1A

(HT)

Ground State Absorption Spectrum of 1,3-

Cyclohexadiene (CHD)

Peak A: 284.2 eV, 1s→1π*(C=C)

Peak B: 287.2 eV, 1s→2π*(C=C)

1s→σ*(C-C,C-H)

2π*

1π*

2π

1s

Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017

Peak A

(1s1π*) Peak B

Pe

ak

A

Pe

ak

B

Carbon K-edge Transient Absorption

Spectra (CHD)

Experiment Theory 1B

Δt = 0 to 40 fs

Peak B

Photon energy / eV

Absorb

ance /

OD

Photon energy / eV

Am

plit

ude /

(arb

. unit)


Peak A

1B State

(2π)

Δt = 90 to 130 fs


Spectra (CHD)

Photon energy / eV

Absorb

ance /

OD

Photon energy / eV

Am

plit

ude /

(arb

. unit)

Experiment Theory 2A


1A

(HT)

Δt = 340 to 540 fs


Spectra (CHD)

Photon energy / eV

Absorb

ance /

OD

Photon energy / eV

Am

plit

ude /

(arb

. unit)

Experiment Theory


CHD 1π*

2π/1π*

HT 1π*

REACTANT

PRODUCT

INTERMEDIATE VALENCE ELECTRONIC

STRUCTURE

(PERICYCLIC MINIMUM)

180 ± 20 fs

110 ± 60 fs


Ultrafast Ring-Opening Deconstructed

O

O

πσ*

Carbon-Carbon Bond Fission Carbon-Heteroatom Bond Fission

1A

1B(ππ*)

2A(π*2)

π→π

*

S0

ππ*

π→π

*

HOMOCYCLIC RING OPENING

IN 1,3-CYCLOHEXADIENE

HETEROCYCLIC RING OPENING

IN FURFURAL

Two Ring-Opening Reactions at 266 nm

Science 356, 6333, 2017 JACS 140, 12538, 2018

2π/1π*

Delayed rise ~ 60 fs

Decay ~110 fs

Ring opening ~ 350 fs

1s→π* 1s→π*

Das David Sven Regina

Attar et al.

Science 356, 6333, 2017

Bhattacherjee et al.

JACS 140, 12538, 2018

Kristina

284.5 eV 285.1 eV 286.4 eV

0.0

Two Ring-Opening Reactions at 266 nm

85

50

30

0

-50

30

10

0

-10

-20

LUMO (2p)

What new science have we learnt?

X-ray vision catches Woodward-

Hoffmann

“The smooth evolution that occurs

in the vicinity of the pericyclic

minimum provides direct

affirmation of the W-H

framework. Moreover, the use

of a convenient tabletop

apparatus bodes well for future x-

ray studies of ultrafast electronic

dynamics.”

Yeston, Chemical Physics Editorial in

Science 356, 54-59, 2017

Discrimination of Ring-opened and

Ring-closed Isomers

“…Experimental studies capable of revealing the dynamics of

photoinduced ring-opening

processes are still in their infancy,

however. The challenges are

substantial…”

“…Without subsequent collisional

relaxation, measurement and

assignment of spectra of the

ring-opened species are

likely to be challenging.”

Ashfold and co-workers

JPCL (Perspective) 8, 3440, 2017

Ring Puckering or Ring Opening?

What about nuclear structural dynamics?

Energ

y

Ele

ctr

onic

What about nuclear structural dynamics?

2. Scattering

Time-resolved Hard X-ray Scattering

Minitti et al. PRL 114, 255501 (2015)

@ Stanford Linear Accelerator (SLAC)

Heteroatom NEXAFS

and

EXAFS

Ultrafast Electron Diffraction Wolf et al. NatChem 11, 504 (2019)

@ Stanford Linear Accelerator (SLAC)

1. Spectroscopy

Complementary Experiments

Pentane-2,4-dione (Acetylacetone)

Intramolecular

O-H···O Hydrogen Bond

(12 kcal mol-1)

Enol (93%) Diketone (7%)

Equilibrium favors the enol form in the vapor phase

Ultrafast Intersystem Crossing in

Acetylacetone (AcAc)

Common chemical features of α,β-enones:

i) Keto-enol tautomerism

ii) Excited state intramolecular proton transfer

iii) Ultrafast excited-state relaxation

Irving et al., Acta Chem. Scand. 24, 589, 1970

Xu et al., JPCA 108, 6650, 2004

Chen et al., JPCA 110, 13, 2006

Poisson et al., JACS 130, 2974, 2008

266 nm-Photodissociation in AcAc

Known so far

Production of OH radicals (~250 ps)

Multiple electronic states involved

Unknown

Role of the triplet state and intersystem crossing timescale

OO

H

+ OH 266 nm · ·

3-penten-2-on-4-yl

radical

Hydroxyl

radical AcAc

266 nm

Carbon K-edge NEXAFS of AcAc

Bhattacherjee, Das, Schnorr, Attar and Leone JACS 139, 46, 2017

1s→π* (LUMO)

1s→Ryd

1s-Core Ionization

1

2

3

4

5

284.4

288.2

286.6

1s→π* (LUMO)

Unique signature of the enol tautomer at 284.4 eV

C3 is chemically shifted from C2 and C4 by ~2 eV

Photon energy / eV

Absorb

ance /

OD

Transient Absorption Spectrum of AcAc

at Carbon K-edge 1 2

3 4

5

6

Early time-delays:

• Ground state depletion (peak 5)

• Appearance of new peaks 3,4,6

Long time-delays:

• Rise of peaks 1and 2

• Decay of peaks 3-6

Intermediate time-delays:

• Gradual decay of peaks 3-6

• Peak 3 broadens at the

lower energy wing

• Onset of new peak 1

Peak 1: 281.4 eV Peak 4: 285.9 eV

Peak 2: 283.8 eV Peak 5: 286.6 eV

Peak 3: 284.7 eV Peak 6: 288.4 eV

Photon energy / eV

ΔA

bso

rba

nce

/ m

OD


Deconstructing AcAc Photophysics

280 282 284 286 288 290

Photon energy / eV

1 2

Faber et al., JChemPhys 151, 144107, 2019


Triplet

state,

ππ*

New Experiments are Benchmarking Theory

Time-dependent Density Functional Theory

Spin-adapted, Equation-of-motion

Coupled-Cluster Singles Doubles

Mapping Chemical Reactions using

Ultrashort, Broadband X-rays



Bhattacherjee, Schnorr, Oesterling, Yang, Xue, Vivie-Riedle and Leone JACS 140, 39, 12538, 2018

Bhattacherjee and Leone AccChemRes 21, 3203, 2018

Stephen R.

Leone

Andrew

Attar

Kirsten

Schnorr

Zheyue

(Marina) Yang

Tian

(Chris) Xue

Leone Group

University of California, Berkeley

Lawrence Berkeley National Laboratory

Future Research Goals

(1) Fundamental Dynamics

of Energy and Charge

(2) Revealing Biological

Function in Real Time

10-15 10-12 10-6 10-3 Time / seconds

Ring Opening and Ring Puckering

Ring Whizzing

Ring-Flip Enzyme Action

Why this? Why now? Why me? Why SLAC?

Excited State Ring Dynamics

Knowledge Gap: Discrimination between ring opening and ring puckering channels

Approach: Time-resolved hard X-ray scattering at MHz repetition rates

Project 1a: Fundamental Dynamics of Energy and Charge

• Nature’s machinery to safely dissipate harmful, excess electronic energy

• Of theoretical interest so far, now within the reach of experiments


Excited State Ring Dynamics - Why Now?

Falahati et al., PCCP 20, 12483, 2018

Marian et al., PCCP 7, 3306, 2005

Satzger et al., PNAS 103, 10197, 2006

Ashfold et al., JPCL 8, 3440, 2017

Oesterling et al., PCCP 19, 2025, 2017

Bhattacherjee et al., JACS 140, 12538, 2018

Experim

ents

Perun et al., JACS 127, 6257, 2005

Perun et al., ChemPhys 313, 107, 2005

Marian et al., PCCP 7 , 3306, 2005


Excited State Ring Dynamics - Why Me? Bhattacherjee and Leone AccChemRes 21, 3203, 2018

Bhattacherjee, Schnorr, Oesterling, Yang, Xue, Vivie-Riedle and Leone JACS 140, 39, 12538, 2018


“No particular X-ray spectral

signatures are obtained to

specifically rule out the ring

puckering channel; however,

the estimates of internal

conversion to the ground

state indirectly set an upper

limit for this pathway”.

Rin

g o

penin

g in 1

00 f

s

Rin

g o

penin

g in 3

50 f

s

Already demonstrated at LCLS: Ring opening and ring closing

New Capability at LCLS-II: Time-resolved hard X-ray scattering at MHz rep rates


Excited State Ring Dynamics - Why SLAC?

Minitti et al., PRL 114, 255501, 2015 Wolf et al., NatChem 11, 504, 2019

Time-resolved hard X-ray scattering (8 keV) Time-resolved MeV electron diffraction

Ring Whizzing Dynamics

Project 1b: Fundamental Dynamics of Energy and Charge

Knowledge Gap: Mechanisms and Timescales?

Approach: Molecular Movie of Ring Whizzing

(using time-resolved hard X-ray scattering at MHz repetition rates)

• Cope rearrangement

• Claisen rearrangement

• Wagner-Meerwein rearrangement

• Pinacol rearrangement

• Benzylic rearrangement

• Beckmann rearrangement

• Schmidt rearrangement

• Baeyer-Villiger rearrangement

• Criegee rearrangement

Moulay ChemEdu 3, 33, 2002

Example of ring-whizzing

Ring Whizzing Dynamics - Why now?


• Restricted to pen-and-paper understanding of structural rearrangements

(Isomerization), molecular fluxionality, C-H bond functionalization, etc.

• No experimental observations for the migration of a group of atoms

• Cope rearrangement

• Claisen rearrangement

• Wagner-Meerwein rearrangement

• Pinacol rearrangement

• Benzylic rearrangement

• Beckmann rearrangement

• Schmidt rearrangement

• Baeyer-Villiger rearrangement

• Criegee rearrangement

Moulay ChemEdu 3, 33, 2002


Time / seconds

10-12 10-6 10-3 10-9

Bhattacherjee, Sneha, Lewis-Borrell, Tau, Clark, and Orr-Ewing

Nature Communications 10, 5152, 2019 (Editors’ Focus on Energy Materials)

Ring Whizzing Dynamics - Why me?

Reaction mechanism of a multistep, photocatalytic

decarboxylation reaction in solution using a

100 kHz infrared laser


Ring Whizzing Dynamics - Why SLAC?

Jiang et al., PRL 105, 263002, 2010

Time-resolved photoionization of acetylene cation using a reaction microscope

@FLASH Germany

1,2

-Hyd

rog

en a

tom

sh

ift

Ibrahim et al., NatCommun 5, 4422, 2014

Coulomb Explosion Imaging of Acetylene Cation @Advanced Light Source Canada

Revealing Enzyme Action

Project 2: Revealing Biological Functions in Real Time

Knowledge Gap: Is a ring flip mechanism operative in catalytic triads?

Approach: Femtosecond serial nanocrystallography at MHz repetition rates

Erez et al., Nature 459, 371, 2009


Revealing Enzyme Action – Why Now?

Ash et al., PNAS 97, 10371, 2000

• Catalytic triads are widely prevalent in the active site of serine hydrolases

• Known to accelerate peptide bond cleavage reactions by a factor of 1010

“Experimental evidence that the flipped rotamer can exist …

…supplied by an x-ray crystal structure of subtilisin BPN9 in 50%

dimethylformamide at low pH…

…In this structure, the imidazole ring is rotated 164°, rather than 180°…”


Revealing Enzyme Action – Why Me?

Bhattacherjee et al., PCCP 18, 27745, 2016

PCCP 17, 20080, 2015


“Diffract before destroy”

Revealing Enzyme Action – Why SLAC?

Ultrafast collective motions in myoglobin upon ligand dissociation

Barends et al., Science 350, 445, 2015

The resolution was 1.8 Å, owing to a temporarily reduced performance of the FEL, which limited the photon energy to 6.9 keV (l = 1.8 Å).

Future Research Goals

10-15 10-12 10-6 10-3 Time / seconds

Ring Opening and Ring Puckering

Ring Whizzing

Ring-Flip Enzyme Action

Why this?

Why now?

Why me?

Why SLAC?

(1) Fundamental Dynamics

of Energy and Charge

(2) Revealing Biological

Function in Real Time

Mainly of theoretical interest / clues in static spectroscopy (ring flip) so far

Now within the reach of time-resolved X-ray experiments

Expertize in ring opening / broaden research horizon (enzyme action)

New opportunities for continued pioneering research in chemical dynamics

Mapping Light-induced Chemical Dynamics in Organic Rings ...

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