Photoisomerization-mechanism-associated excited-state hydrogen transfer in 2′-hydroxychalcone revealed by on-the-fly trajectory surface-hopping molecular dynamics simulation

By performing global-switching on-the-fly trajectory surface-hopping molecular dynamics simulation at the OM2/MRCI (14,15) quantum level, we probed the S-3(pi pi*) photoisomerization mechanisms associated with excited-state intramolecular hydrogen transfer for 2 '-hydroxychalcone (2HC) within the interwoven conical intersection networks from four singlet electronic states (S-3, S-2, S-1, and S-0). The simulated quantum yields of 0.03 for cis-to-trans and zero for trans-to-cis photoisomerization were due to almost all the conical intersections being localized either in the cis-2HC or in trans-2HC region, and there was little chance for sampling trajectories to reach the rotation conical intersection (S-1/S-0) in between cis-2HC and trans-2HC that is key for reactive isomerization. The potential energy well on the S-1 state in the trans-2HC region prevents trajectories from trans-to-cis photoisomerization, while the fact there is no well on S-1 state in cis-2HC region opens a few chances for trajectories to reach the rotation conical intersections. The present simulation found that excited-state intramolecular hydrogen transfers in 2HC have a negative impact for reactive isomerization, and that hydrogen transfers take place on the S-1 state, while back-transfer on the S-0 state prevents sampling trajectories reaching rotational conical intersections. It was realized that it could be possible to enhance the quantum yield of 2HC photoisomerization by suppressing the hydrogen transfer (such as by changing an electron-donating substitution or adjusting the substitution position to decrease the acidity of the phenol group). From a perspective view of the potential energy surfaces, the theoretical design of such 2HC derivatives could enhance (control) the quantum yield by shifting the conical intersections away from the cis- and trans-region.

Automated summary

By performing global-switching on-the-fly trajectory surface-hopping molecular dynamics simulation at the OM2/MRCI quantum level, the study probed the S-3(pi pi*) photoisomerization mechanisms associated with excited-state intramolecular hydrogen transfer for 2'-hydroxychalcone (2HC). The simulation found that the quantum yields of cis-to-trans and trans-to-cis photoisomerization were low due to the conical intersections being localized in either the cis-2HC or trans-2HC region, suggesting potential strategies to enhance the quantum yield of 2HC photoisomerization by suppressing hydrogen transfer and shifting conical intersections.