Coherent ultrafast torsional motion and isomerization of a biomimetic dipolar photoswitch.
Femtosecond fluorescence up-conversion, UV-Vis and IR transient absorption spectroscopy are used to study the photo-isomerization dynamics of a new type of zwitterionic photoswitch based on a N-alkylated indanylidene pyrroline Schiff base framework (ZW-NAIP). The system is biomimetic, as it mimics the photophysics of retinal, in coupling excited state charge translocation and isomerization. While the fluorescence lifetime is 140 fs, excited state absorption persists over 230 fs in the form of a vibrational wavepacket according to twisting of the isomerizing double bond. After a short "dark" time window in the UV-visible spectra, which we associate with the passage through a conical intersection (CI), the wavepacket appears on the ground state potential energy surface, as evidenced by the transient mid-IR data. This allows for a precise timing of the photoreaction all the way from the initial Franck-Condon region, through the CI and into both ground state isomers, until incoherent vibrational relaxation dominates the dynamics. The photo-reaction dynamics remarkably follow those observed for retinal in rhodopsin, with the additional benefit that in ZW-NAIP the conformational change reverses the zwitterion dipole moment direction. Last, the pronounced low-frequency coherences make these molecules ideal systems for investigating wavepacket dynamics in the vicinity of a CI and for coherent control experiments.
Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, Strasbourg University, CNRS, IPCMS-DON, 23, rue du Loess, 67034 Strasbourg, France.
Julien
J
Briand
Olivier
O
Bräm
Julien
J
Réhault
Jérémie
J
Léonard
Andrea
A
Cannizzo
Majed
M
Chergui
Vinizio
V
Zanirato
Massimo
M
Olivucci
Jan
J
Helbing
Stefan
S
Haacke
D000042:Absorption; D040761:Biomimetic Materials / Q000737:chemistry*; D007536:Isomerism; D012172:Retinaldehyde / Q000737:chemistry; D012243:Rhodopsin / Q000737:chemistry; D012545:Schiff Bases / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
D012545:Schiff Bases; D012243:Rhodopsin; D012172:Retinaldehyde