Cervetto Valentina, Bregy Harald, Hamm Peter, Helbing Jan
Physikalisch-Chemisches Institut, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
J Phys Chem A. 2006 Oct 12;110(40):11473-8. doi: 10.1021/jp062856h.
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.
利用时间分辨红外光谱研究了在D2O中N-甲基硫代乙酰胺（NMTAA）在n-π（S1）和π-π（S2）电子跃迁的选择性激发下，顺式→反式和反式→顺式方向的光异构化过程。在D2O中，对顺式和反式NMTAA进行π-π激发时，异构化和回到基态发生在两个不同的时间尺度上（≤8皮秒，约250皮秒），而在n-π激发时，仅在较慢的时间尺度上观察到基态恢复。反式→顺式异构化的量子效率为30-40%，与激发的电子态无关，而顺式→反式异构化的量子效率为60-70%。这些结果支持了一种异构化通过一个与电子激发能和初始构象无关的共同中间态发生的机制。
