Optical Control of Crossing the Conical Intersection in β-Carotene

Optical coherent quantum control of ultrafast protein electron transfer

The optical control of a biological system has been challenging, although the control of the energy transfer and isomerization reaction has been successfully demonstrated. Here, we report on our studies of ultrafast electron-transfer (ET) dynamics in a protein flavodoxin as a function of optical pump-pulse chirp. With a transform-limited excitation pulse in 25 femtoseconds, we observed the excited-state wave packet dynamics in ET reactions with a dephasing time within 1 ps. By modulating the phase of the excitation pulses, the ultrafast ET dynamics was found to change from 100 to 300 fs due to the different wave packets prepared by chirped pulses. We further found that the coherent control through the modulated wave packets can propagate into the subsequent back ET reactions resulting in the dynamics varying from 500 to 800 fs. This successful demonstration of coherent controlled ET reactions paves the way to control a variety of complex ET processes in chemical and biological systems.

Optical Quantum Control of the Electron Transfer Reactions in Protein Flavodoxin

The optical quantum control has been successfully applied in modulating biological processes such as energy transfer and bond isomerization. Among the reactions in realizing biological functions, the electron transfer (ET) process is fundamental; hence, the quantum control over such an ET reaction is of far-reaching significance. Here, we realized optical quantum control over ultrafast ET processes in a protein, flavodoxin, by applying various chirped excitation pulses. We observed the wavepacket dynamics within a dephasing time of less than 1 ps. Within this time window, we found that the ultrafast photoinduced ET reaction can be controlled by different chirped excitations with a rate change by a factor of about 2. Furthermore, the control effect is propagated into the subsequent ultrafast back ET reaction, showing a variation of the BET dynamics with different excitation chirps. The underlying mechanism is the initial wavepacket dynamics; the differently prepared wavepackets with chirped excitation evolve along various pathways, resulting in the changes of ET rates. The successful demonstration of optical quantum control of ultrafast biological ET is significant and opens a new avenue to explore the quantum control of real biological ET reactions.

A Local Diabatisation Method for Two-State Adiabatic Conical Intersections

A methodology to locally characterize conical intersections (CIs) between two adiabatic electronic states for which no nonadiabatic coupling (NAC) vectors are available is presented. Based on the Hessian and gradient at the CI, the branching space coordinates are identified. The potential energy surface around the CI in the branching space is expressed in the diabatic representation, from which the NAC vectors can be calculated in a wave-function-free, energy-based approach. To demonstrate the universality of the developed methodology, the minimum-energy CI (MECI) between the first (S1) and second (S2) singlet excited states of formamide is investigated at the state-averaged complete active space self-consistent field (SA-CASSCF) and extended multistate complete active space second-order perturbation theory (XMS-CASPT2) levels of theory. In addition, the asymmetrical MECI between the ground state (S0) and S1 of cyclopropanone is evaluated using SA-CASSCF, as well as (ME)CIs between the S1 and S2 states of benzene using SA-CASSCF and time-dependent density functional theory (TDDFT). Finally, a CI between the S1 and S2 excited states of thiophene was analyzed using TDDFT.