Benzene Photochemistry:

1
Benzene Photochemistry
Ultrafast Intersystem Crossing
Dorian Parker Fielding Group Co Co Chem 10th
April 2008
2
Jablonski Diagram
sN
s1
T1
Energy
A
s0
Fluorescence (channel 1 decay) ns Intersystem
Crossing (channel 2 decay) 100s ns-ms Internal
Conversion fs-ps Phosphorescence s
3
Benzenes Channel 3 mystery
4
Time-resolved photoelectron spectroscopy
5
Benzene S1 decay dynamics
6
Benzene S1 photochemistry
7
Increasing the probe energy
Slow Decay Relative amplitude
235
255
245
Probe energy (nm)
Change from 254 nm to 235 nm increase of 0.4 eV
Takes us 1.14 eV above ion limit Compared to
4.75 eV vibrational energy of Ground State from
Internal Conversion
8
Benzene S1 photochemistry
9
Photoelectron Spectrum
10
Fourier Analysis
Oscillation Amplitude
0.35
1.55
eKE (eV)
11
D0
0.4 eV
S1
1.2 ps
12
Isomerisation?
13
Intersystem crossing?
14
Intersystem crossing
15
Summary

• Observed coherent oscillation between two
  different states of benzene using TRPES
• Discovery of ultrafast intersystem crossing
• Channel three not due to IC at least in this
  transition region

16
Acknowledgements
Russell Minns, Helen Fielding (UCL)
Graham Worth, Tom Penfold (Birmingham) Mike
Robb, Mike Bearpark, Benjamin Lasorne (Imperial)
EPSRC, UCL