Electronic Energy Funnels in Cis−Trans Photoisomerization of Retinal Protonated Schiff Base

Abstract

The photoinduced cis−trans isomerization of all-trans retinal protonated Schiff base is studied using the full multiple spawning method. Our model allows for two classes of electronic transitions: exciton migration and quenching by coupling of the electronic and nuclear degrees of freedom. We find that quenching and exciton transfer are two temporally disjoint events and that exciton transport is highly directed. The observed selectivity in photoproducts is interpreted in terms of an electronic energy “funnel”, which is attributed to the Schiff base. The limits of the concept of an electronic energy “funnel”, when electron−phonon coupling is strong, are discussed and it is argued that such funnels can induce selectivity in excitation migration even when thermodynamic equilibrium among the excited electronic states is not reached.

Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

“…Martinez and co-workers reported that the photoexcitation of ethylene evolves to a twisted geometry with charge-separated character and nonradiatively quenches to the ground state through a conical intersection. 50 Following this idea, we proposed that photoexcited PANI will relax to a geometrically distorted intermediate state that involves torsional motions between the adjacent rings. 34 The lack of a significant transition dipole from this state facilitates nonradiative recovery to the ground state whose slow rate may reflect motion through a conical intersection.…”

Classical Fluctuating Charge Theories: The Maximum Entropy Valence Bond Formalism and Relationships to Previous Models

“…Going from a wave function-based description to a classical electrostatic representation is a simple matter of integration, but the reverse classical f quantum transformation is problematic because the map is obviously not information-preserving. In our previous attempts along these lines, 32 we have used model wave functions that were stored (and could be perturbed if necessary). While this is reasonable for special cases, such as a quantum solute in a classical solvent, it will clearly become cumbersome when the classical region is not composed of many chemically identical molecules.…”

A vision for ultrafast photoisomerization

“…The computational burden of evolving the photoexcited state in a fully-correlated methodology is significant [11]. We are hopeful that direct evolution of the photoexcited wavefunction or advances like the DMRG algorithm [27] which allow one to include electron-electron interactions in tight-binding models will permit explicit calculations for realistic [14] and interesting molecules such as those considered here.…”

“…This method of inferral excludes CH vibrations and modes where the hydrogen oscillates out of phase with its carbon but is good for acoustical vibrations and torsional vibrations where the hydrogen's contribution to the moment of inertia is roughly equal to the carbon's. Inferring hydrogen positions excludes sp 3 hybridization which is important for de-excitation [11]. Photoexcitation energy gaps are presented in Figure 4.…”

“…Although excellent at describing the ground state properties, these approaches struggle to treat photoexcited states [9]; for example, "scissor operators" are used to enlarge gap energies [10] and molecular dynamics in the photoexcited state is difficult for large molecules [11].…”