In this work, we investigate the dual hydrogen bonded 1,4-bis-(3-hydroxy-4-oxo-4H-chromen-2-yl)-benzene (bisflavonol) system in detail. Via optimizing stable structures and constructing potential energy curves, we confirm that two primary structures (i.e., anti-bisflavonol and syn-bisflavonol) can coexist in the S₀ state. Calculating the reduced density gradient (RDG) versus sign(λ₂)ρ and gradient isosurfaces, we confirm the formation of double hydrogen bonds for both anti-bisflavonol and syn-bisflavonol. Comparing the primary geometrical parameters involved in hydrogen bonds, we verify that the double intramolecular hydrogen bonds should be strengthened in the S₁ state. In view of the photo-excitation process, we find that the charge redistributions around the hydrogen bonded moieties of both anti-bisflavonol and syn-bisflavonol facilitate the excited state intramolecular proton transfer (ESIPT) reaction. Given the reaction paths for the ESIPT process, the S₀-state and S₁-state potential energy surfaces (PESs) are constructed for both anti-bisflavonol and syn-bisflavonol along with two hydrogen bonds to reveal the overall excited state dynamical behavior. Searching for the transition state (TS) structure and calculating the intrinsic reaction coordinate (IRC) energetic profile, we confirm the ESIPT reaction. Combining it with Born–Oppenheimer molecular dynamics (BOMD) simulations, we study the ESIPT dynamical behaviors in detail. We present that only the single proton transfer process occurs in the S₁ state in aprotic solvents, which makes up for the deficiency of previous experiments. The theoretical electronic spectra further confirm our attribution. This work not only illustrates that anti-bisflavonol and syn-bisflavonol coexisting in the S₀-state can promote the respective ESIPT reaction, but also makes a new attribution to previous experiments.

We theoretically study the dynamical speedup of a quantum system in a nonequilibrium environment. Based on the trace distance, we derive the generalized Margolus-Levitin and Mandelstam-Tamm types of bounds on the quantum speed limit time of a quantum system evolving from an arbitrary initial state. We demonstrate that the mechanism for the speedup of dynamical evolution is closely associated with both the energy of the system and exchange of information between the system and its environment. It is shown that the nonequilibrium feature of the environment can speed up the quantum evolution in both Markovian and non-Markovian dynamics regions. We emphasize that the non-Markovian effect of the system dynamics is neither necessary nor sufficient to speed up the quantum evolution in a nonequilibrium environment.

In the present work, we theoretically illuminate the excited state double proton transfer (ESDPT) process about a novel synthesized system 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol (BBTD). Minor changes of both structure and charge redistribution deriving from photoexcitation result in obviously different excited state dynamical process. Exploration about our constructed S₁-state potential energy surface (PES) indicates a stepwise ESDPT mechanism for BBTD. In addition, we present a new mechanism about regulating and controlling stepwise ESDPT process via external electric field.

We derive a distinct bound of the quantum speed limit for a non-Hermitian quantum system by employing the gauge invariant and geometric natures of quantum mechanics. The bound is of geometric properties since it relates to the geometric phase of the quantum system, and it is tighter than the Mandelstam-Tamm and Margolus-Levitin bounds in some cases. Also, by making the geodesic assumption, the analog of the Margolus-Levitin bound is derived for the time-dependent (non-)Hermitian quantum system. These two bounds reflect the impacts of the transmission modes of the state vectors on the evolution path in the manifold.