ULTRAFAST DYNAMICS IN NITRO- AND (ORGANOPHOSPHINE)GOLD(I)-POLYCYCLIC

AROMATIC HYDROCARBONSR. Aaron Vogt, Christian Reichardt, Carlos E. Crespo-Hernández,

Thomas G. Gray

Department of Chemistry, Case Western Reserve University

Molecular Spectroscopy Symposium - June 21, 2011

2

Jablonski Diagram

S0

S1

Sn

Tn

ISC

IC Fluorescence

Phosphorescence

IC

ISC

VC

IC = Internal ConversionISC = Intersystem Crossing

3

Transient Absorbance: Pump Probe

S0

S1

Sn

Pump

Probe

kic

4

Transient Absorbance: Pump Probe

S0

S1

Sn

Pump

Probe

kic

5

Transient Absorbance: Pump Probe

S0

S1

Sn

Pump

Probe

kic

6

S0

Ground State

S1* Excited State S1

Dissociative State

T3

Excited State

ArO·NO·

T1*

Vibrationally-Excited State

T1

Relaxed State

1 Reichardt, C., Vogt, R.A., Crespo-Hernández, C. E., J. Chem. Phys. 2009, 131, 224518.2 Hurley, R., Testa, A.C. J. Am. Chem. Soc. 1968, 90, 1949.

Kinetic Mechanism of the nitronaphthalenes1

Absorption

Internal Conversion

Vibrational Cooling

ConformationalRelaxationISC

63%2

Dissociation

ISC

Absorption

0

10

20

0

10

20

30

400 500 6000

5

Time delay (ps) 0.00to 0.77

2NNAcetonitrile

Time delay (ps) 0.00to 0.80

2M1NN

1NN

A (10

-3)

Wavelength (nm)

Time delay (ps) 0.00to 0.87

Fast UV rise - nitronaphthalenes

0

5

10

0

20

40

400 500 6000

5

Time delay (ps) 0.00 to 0.80

2NN

Cyclohexane

Time delay (ps) 0.00 to 0.80

2M1NN

1NN

A (

10-3

)

Wavelength (nm)

Time delay (ps) 0.00 to 0.90

Cyclohexane Acetonitrile

Molecule τ1 (fs) τ1 (fs)

2NN 110 ± 10 140 ± 101NN 110 ± 50 140 ± 502M1NN 370 ± 70 210 ± 30

S0

Ground State

S1* Excited State

T3

Excited State

S1

Dissociative State

7

• *1 fs = 1 femtosecond = 10-15 s (= 0.000000000000001 s)• Fast rise occurs in wide variety of solvents• Lifetime of ~150 fs*

8

01020

30

0

10

20

30

400 500 6000

3

6

Time delay (ps) 0.8 to 14 31

2NNAcetonitrile

Time delay (ps) 0.8 to 37 75

2M1NN

1NN

A (10

-3)

Wavelength (nm)

Time delay (ps) 0.9 to 12 24

Internal Conversion and Vibrational Cooling

0

10

20

0

20

40

400 500 6000

4

8

Time delay (ps) 0.8 to 11 35

2NNCyclohexane

Time delay (ps) 0.8 to 30 85

2M1NN

1NN

A (10

-3)

Wavelength (nm)

Time delay (ps) 0.9 to 25 49

Cyclohexane AcetonitrileMolecule τ2 (ps) τ2 (ps)

2NN 2.1 ± 0.1 2.0 ± 0.11NN 2.3 ± 0.2 2.8 ± 0.22M1NN 1.4 ± 0.3 0.6 ± 0.1

T3

Excited State

T1*

Vibrationally-Excited State

T1

Relaxed State

IC

VC

Cyclohexane AcetonitrileMolecule τ3 (ps) τ3 (ps)

2NN 10 ± 1 12.3 ± 0.21NN 10.3 ± 0.3 11.2 ± 0.42M1NN 7.1 ± 0.9 5.9 ± 0.3

9

τ3: Vibrational Cooling-Evidence

350 400 450 5000.0

0.5

1.0

500 550 600 6500.0

0.5

1.0

500 550 600 6500.0

0.5

1.0

Wavelength (nm)

Time delay (ps) 20 27 36 62

2NN

Wavelength (nm)

Time Delay (ps) 4 9 24

1NN

A (10

-3)

A (10

-3)

A (10

-3)

Wavelength (nm)

Time delay (ps) 1.8 4.4 12 25

2M1NN

Normalized triplet spectra for molecules in cyclohexane

T1*

Vibrationally-Excited State

T1

Relaxed State

Vibrational Cooling

Cyclohexane AcetonitrileMolecule τ3 (ps) τ3 (ps)

2NN 10 ± 1 12.3 ± 0.21NN 10.3 ± 0.3 11.2 ± 0.42M1NN 7.1 ± 0.9 5.9 ± 0.3

10

Au naphthalenes

Mono

C2h

11

hν

ISC

IC

VC

S0

S1

Tn

T1

τ1: Fast rise-Au naphthalenes

0

2

4

6

8

350 400 450 500 550 600 650

0

2

4

6

Time delay (ps) 0.00 to 0.87

Mono

A (

10-3)

Wavelength (nm)

Time delay (ps) 0.00 to 0.80C2h

τ1 (fs)

Mono 300 ± 50

C2h 180 ± 50

12

Internal Conversion and Vibrational CoolingAu naphthalenes

hν

ISC

IC

VC

S0

S1

Tn

T1

0

2

4

6

8

10

350 400 450 500 550 600 6500

2

4

6

8

10

Time delay (ps) 0.87 1.03 1.4 2.3 6.2 19 200

Mono

A (

10-3)

Wavelength (nm)

Time delay (ps) 0.80 1.3 1.7 2.1 3.2 5.4 10 30

C2h

τ2 (ps) τ3 (ps)

Mono 0.98 ± 0.05 8.7 ± 0.5

C2h 1.9 ± 0.2 5.1 ± 0.8

13

400 420 440 460

0.7

0.8

0.9

1.0

420 440 460 480

0.6

0.8

1.0

Wavelength (nm)

Time delay (ps) 4 7 15 40

Mono

A (

10-3)

A (

10-3)

Wavelength (nm)

Time delay (ps) 4 6 10 41

C2h

τ3: Vibrational Cooling-Evidence

τ3 (ps)

Mono 8.7 ± 0.5

C2h 5.1 ± 0.8

VC spectra features• Blue shift• Narrowing

14

ISC

Kinetic Mechanism of 1-Nitronaphthalene:Supporting Calculations S0

Ground State

S1* Excited State

T3

Excited State

T1*

Vibrationally-Excited State

T1

Relaxed State

Absorption

Internal Conversion

Vibrational Cooling

S1

Dissociative State

ConformationalRelaxation

Calculated PES for nitronaphthalenes in acetonitrile. The nitro-aromatic torsion angle was fixed while all other coordinates were optimized. B3LYP/IEFPCM/6-311++G(d,p)//TD-PBE0/NE-IEFPCM(Acetonitrile)

15

ISC

Kinetic Mechanism of 1-Nitronaphthalene:Supporting Calculations S0

Ground State

S1* Excited State

T3

Excited State

T1*

Vibrationally-Excited State

T1

Relaxed State

Absorption

Internal Conversion

Vibrational Cooling

S1

Dissociative State

ConformationalRelaxation

Calculated PES for nitronaphthalenes in acetonitrile. The nitro-aromatic torsion angle was fixed while all other coordinates were optimized. B3LYP/IEFPCM/6-311++G(d,p)//TD-PBE0/NE-IEFPCM(Acetonitrile)

16

DFT Calculations

Calculated PES for nitronaphthalenes in acetonitrile. The nitro-aromatic torsion angle was fixed while all other coordinates were optimized. B3LYP/IEFPCM/6-311++G(d,p)//TD-PBE0/NE-IEFPCM(Acetonitrile)

1NN 2NN

17

DFT Calculations

Calculated PES for nitronaphthalenes in acetonitrile. The nitro-aromatic torsion angle was fixed while all other coordinates were optimized. B3LYP/IEFPCM/6-311++G(d,p)//TD-PBE0/NE-IEFPCM level of theory.

1NN 2NN

18

DFT Calculations

hν

ISC

IC

VC

S0

S1

Tn

T1

Mono (eV) C2h (eV)S1 4.32 (0.089) 4.13 (0.292)Tn 4.27 4.11

TD-PBE0/IEFPCM/(TZVP, Stuttgart on Au)

Mono

C2h

19

hν

ISC~10-110 ps

Fast IC

S0

S1

T3

T1

S2 IC~200 fs

Comparison between naphthalene and pyrene derivatives

Crespo-Hernández Carlos, E.; Burdzinski, G.; Arce, R. J. Phys. Chem. A 2008, 112, 6313.Vogt, R. A.; Peay, M. A.; Gray, T. G.; Crespo-Hernandez, C. E. J. Phys. Chem. Lett. 2010, 1, 1205.

hν

ISC~7 ps

Fast IC

S0

S1

T3

T1

CR~100 fs

20

Conclusions

hν

ISC

IC

VC

S0

S1

Tn

T1

Nitronaphthalenes General Mechanism

S1Tn

VC

IC

Nitro-Aromatic Torsion Angle

En

erg

y T1

2NN

1NN

2M1NN

S0

ArO·+

NO·

Products

21

Acknowledgements

• ACS Petroleum Research Fund• Case Western Reserve University• Crespo Group• Gray group

22

23

Comparison between naphthalene and pyrene derivatives

1-nitropyrene mechanism proposed byCrespo-Hernández and coworkers

Refs

Experimental Setup

• Helios and Eos are from Ultrafast Systems, LLC• Integra is from Quantronix• TOPAS is from Quantronix/Light Conversion

24

N

O

O

N

O

O

O

N O

(1)

O + NO

(3)

(2)

N

O

OX

(parallel)

(perpendicular)

Background and SignificanceChapman’s Orientation-Photoreactivity Relationship1

25

Schematic representation of Chapman’s Orientation-Photoreactivity relationship in the photochemistry of nitro-PAHs

1 Chapman, O. L.; Heckert, D. C.; Reasoner, J. W.; Thackaberry, S. P.. J. Am. Chem. Soc. 1966, 88, 5550.

oxaziridine-type transition state

nitric oxide

nitrite intermediate

aryloxy radical

26

DFT Calculations

Calculated PES for nitronaphthalenes in acetonitrile. The nitro-aromatic torsion angle was fixed while all other coordinates were optimized. B3LYP/IEFPCM/6-311++G(d,p)//TD-PBE0/NE-IEFPCM level of theory.

1NN 2NN