Perpendicular State of an Electronically Excited Stilbene: Observation by Femtosecond-Stimulated Raman Spectroscopy.
In the photoisomerization path of stilbene, a perpendicular state P on the S1potential energy surface is expected just before internal conversion through a conical intersection S1/S0. For decades the observation of P was thwarted by a short lifetime τPin combination with slow population flow over a barrier. But these limitations can be overcome by ethylenic substitution. Following optical excitation of trans-1,1'-dicyanostilbene, P is populated significantly (τP= 27 ps in n-hexane) and monitored by an exited-state absorption band at 370 nm. Here we report stimulated Raman lines of P. The strongest, at 1558 cm-1, is attributed to stretching vibrations of the phenyl rings. Transient electronic states, resonance conditions, and corresponding Raman signals are discussed.
Department of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Str. 2, D-12489 Berlin, Germany.
Martin
M
Quick
Department of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Str. 2, D-12489 Berlin, Germany.
Alexander L
AL
Dobryakov
Department of Chemistry, Lomonosov Moscow State University , Moscow 119991, Russia.
Ilya N
IN
Ioffe
Firefly Project , Moscow 117593, Russia.
Alex A
AA
Granovsky
Department of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Str. 2, D-12489 Berlin, Germany.
Sergey A
SA
Kovalenko
Department of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Str. 2, D-12489 Berlin, Germany.
Nikolaus P
NP
Ernsting