Photofragmentation Dynamics in Solution Probed by Transient IR Absorption Spectroscopy: πσ*-Mediated Bond Cleavage in p-Methylthiophenol and p-Methylthioanisole.
The 267 nm photodissociation dynamics of p-methylthiophenol (p-MePhSH) and p-methylthioanisole (p-MePhSMe) dissolved in CD3CN have been probed by subpicosecond time-resolved broadband infrared spectroscopy. Prompt (τ < 1 ps) S-H bond fission in p-MePhSH is confirmed by monitoring the time-evolution of the parent (S0) bleach and the transient absorption of the p-MePhS products. Vibrational relaxation of the latter occurs on a ∼8.5 ps time scale, and ∼40% of the total radical population undergoes geminate recombination over a ∼150 ps time scale, yielding (mainly) the p-MePhSH(S0) parent. S-Me bond fission following photoexcitation to the S1 state of p-MePhSMe occurs over a much longer timescale, with a rate that is very dependent on the degree of vibrational excitation within S1. The various findings are compared and contrasted with results from complementary gas-phase photofragmentation studies of both molecules, which are shown to provide a valuable starting point for describing the solution-phase dynamics.
†School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
Daniel
D
Murdock
†School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
Stephanie J
SJ
Harris
†School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
Tolga N V
TN
Karsili
‡Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, United Kingdom.
Gregory M
GM
Greetham
‡Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, United Kingdom.
Ian P
IP
Clark
‡Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, United Kingdom.
Michael
M
Towrie
†School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
Andrew J
AJ
Orr Ewing
†School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom.
Michael N R
MN
Ashfold
kinetics; photodissociation; solution-phase photochemistry; thioanisoles; thiophenols; ultrafast pump−probe spectroscopy