Coherent photoisomerization and quantum yield of biomimetic molecular switches

Photoisomerizing molecular switches convert light energy into mechanical energy at the molecular level. In coherent photoisomerization, the energy is impulsively funnelled into a small number of vibrational modes, so that vibrational wave packets are observed throughout the reaction. Observing wavepackets in the photoproduct ground ground state, which requires the excited state coherence to survive the passage through the conical intersection, was so far observed for rhodopsin (Rho) only. However, using ultrafast pump-probe transient absorption (TA) spectroscopy it was recently demonstrated to occur also in small artificial photoswitches in solution. These were based on an indanylidene-pyrroline (IP) chemical skeleton, where a pyrole ring is linked to an indanone moiety via a single double carbonyl bond C₁´=C₁. It was shown by ab initio quantum chemical calculations that IP derivatives are able to reproduce the excited state (S₁) potential energy surface of retinal in rhodopsin.