Time-resolved IR spectroscopy of N-methylthioacetamide: trans-->cis isomerization upon n-pi and pi-pi excitation and cis-->trans photoreaction.
Time-resolved infrared spectroscopy was used to study the photoisomerization of N-Methylthioacetamide (NMTAA) in D2O in both the cis-->trans and the trans-->cis direction upon selective excitation of the n-pi (S1) and pi-pi (S2) electronic transitions. While isomerization and the return to the ground state takes place on two distinct time scales (<or=8 ps, approximately 250 ps) upon pi-pi excitation of both cis- and trans-NMTAA in D2O, ground state recovery is only observed on the slower time scale upon n-pi excitation. The quantum efficiency for trans-->cis isomerization is 30-40%, independent of the electronic state excited, while the cis-->trans isomerization proceeds with a 60-70% quantum efficiency. These results support a mechanism by which isomerization takes place via one common intermediate state independent of electronic excitation energy and initial conformation.
Cervetto
Valentina
V
Physikalisch-Chemisches Institut, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Bregy
Harald
H
Hamm
Peter
P
Helbing
Jan
J
D007536:Isomerism; D010777:Photochemistry; D013055:Spectrophotometry, Infrared; D013853:Thioacetamide / Q000031:analogs & derivatives* / Q000737:chemistry; D013997:Time Factors
C492098:N-methylthioacetamide; D013853:Thioacetamide