Excited-state Dynamics Simulations Research Articles

Photoinduced Electron-Nuclear Dynamics of Fullerene and Its Monolayer Networks in Solvated Environments.

The recently synthesized monolayer fullerene network in a quasi-hexagonal phase (qHP-C60) exhibits superior electron mobility and optoelectronic properties compared to molecular fullerene (C60), making it highly promising for a variety of applications. However, the microscopic carrier dynamics of qHP-C60 remain unclear, particularly in realistic environments, which are of significant importance for applications in optoelectronic devices. Unfortunately, traditional ab initio methods are prohibitive for capturing the real-time carrier dynamics of such large systems due to their high computational cost. In this work, we present the first real-time electron-nuclear dynamics study of qHP-C60 using velocity-gauge density functional tight binding, which enables us to perform several picoseconds of excited-state electron-nuclear dynamics simulations for nanoscale systems with periodic boundary conditions. When applied to C60, qHP-C60, and their solvated counterparts, we demonstrate that water/moisture significantly increases the electron-hole recombination time in C60 but has little impact on qHP-C60. Our excited-state electron-nuclear dynamics calculations show that qHP-C60 is extremely unique and enable exploration of time-resolved dynamics for understanding excited-state processes of large systems in complex, solvated environments.

Machine-Learning Accelerated Description of Polarons in 2D Lead Halide Perovskites

MLFF-based MD trajectories to compute NAC and excited-state dynamics. At each stage, results based on machine learning are compared to traditional ab initio based electronic dissipative dynamics.The limits of this method are explored as we increase the timescale of the calculation beyond those allowed by ab initio molecular dynamics and to determine the effectiveness of MLFF-MD when used for excited-state nonadiabatic dynamics simulations using atomistic models that include charge injection or when an excited-stated potential energy surface is used to account for changes due to an excitation.

Construction of Highly Accurate Machine Learning Potential Energy Surfaces for Excited-State Dynamics Simulations Based on Low-Level Data Sets.

Machine learning is capable of effectively predicting the potential energies of molecules in the presence of high-quality data sets. Its application in the construction of ground- and excited-state potential energy surfaces is attractive to accelerate nonadiabatic molecular dynamics simulations of photochemical reactions. Because of the huge computational cost of excited-state electronic structure calculations, the construction of a high-quality data set becomes a bottleneck. In the present work, we first built two data sets. One was obtained from surface hopping dynamics simulations at the semiempirical OM2/MRCI level. Another was extracted from the dynamics trajectories at the CASSCF level, which was reported previously. The ground- and excited-state potential energy surfaces of ethylene-bridged azobenzene at the CASSCF computational level were constructed based on the former low-level data set. Although non-neural network machine learning methods can achieve good or modest performance during the training process, only neural network models provide reliable predictions on the latter external test data set. The BPNN and SchNet combined with the Δ-ML scheme and the force term in the loss functions are recommended for dynamics simulations. Then, we performed excited-state dynamics simulations of the photoisomerization of ethylene-bridged azobenzene on machine learning potential energy surfaces. Compared with the lifetimes of the first excited state (S1) estimated at different computational levels, our results on the E isomer are in good agreement with the high-level estimation. However, the overestimation of the Z isomer is unimproved. It suggests that smaller errors during the training process do not necessarily translate to more accurate predictions on high-level potential energies or better performance on nonadiabatic dynamics simulations, at least in the present case.

Tautomeric enhancement of 2-(1H-pyrazol-5-yl)pyridine in photoinduced proton transfer by water-assisted molecules

Theoretical insight of excited state proton transfer (ESPT) in 2-(1H-pyrazol-5-yl)pyridine abbreviated as PPP interacting with water wires: PPP(H2O)n where n = 13 has been presented in both static and dynamics studies. Explicit water molecules placed around PPP have been simulated to elucidate the intermolecular hydrogen bonding interactions between them. Hydrogen bond strengthening in the excited state (S1) has been verified by shorter bond distances and redshift of IR vibrational spectra involving the proton transfer (PT) process. Furthermore, on-the-fly excited state dynamics simulations of all complexes have been performed to provide detailed information on the PT mechanism. The dynamic results show that one water molecule added to the neighboring PPP as an intermolecular hydrogen bonding bridge can promote double excited state intermolecular proton transfer up to 36% compared with its intrinsic intramolecular hydrogen bond of the PPP system. Meanwhile adding a second or third water molecule could decrease the probabilities of PT. Especially in PPP(H2O)3, a rearrangement of water molecules is observed that PT occurs via one water molecule. Hence, the models with explicit water molecules interacting with PPP as intermolecular hydrogen bonding bridge are a great representative role played by water molecules of the PT process at the molecular level.

The nature of carotenoid S* state and its role in the nonphotochemical quenching of plants

In plants, light-harvesting complexes serve as antennas to collect and transfer the absorbed energy to reaction centers, but also regulate energy transport by dissipating the excitation energy of chlorophylls. This process, known as nonphotochemical quenching, seems to be activated by conformational changes within the light-harvesting complex, but the quenching mechanisms remain elusive. Recent spectroscopic measurements suggest the carotenoid S* dark state as the quencher of chlorophylls’ excitation. By investigating lutein embedded in different conformations of CP29 (a minor antenna in plants) via nonadiabatic excited state dynamics simulations, we reveal that different conformations of the complex differently stabilize the lutein s-trans conformer with respect to the dominant s-cis one. We show that the s-trans conformer presents the spectroscopic signatures of the S* state and rationalize its ability to accept energy from the closest excited chlorophylls, providing thus a relationship between the complex’s conformation and the nonphotochemical quenching.

Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations.

Single-walled carbon nanotubes (SWCNTs) functionalized with sparse surface chemical groups are promising for a variety of optical applications such as quantum information and bio-imaging. However, the luminescence efficiencies and stability, two key aspects, undoubtedly govern their practical usage. Herein, we assess the surface migration of oxygen and triazine groups on as-modified SWCNT fragments by adopting transition state theory and explore the de-excitation of oxygen-functionalized SWCNT fragments by performing non-adiabatic excited-state dynamics simulations. According to the predicted moderate or even small reaction barriers, the migration of both oxygen and triazine groups is feasible from an sp3 defect configuration forming an energetically more stable sp2 configuration at moderate or even room temperatures. Such isomerization leads to drastically different light emission capabilities as indicated by the large or zero oscillator strengths. During the dynamics simulations, the lowest excited singlet (S1) state rapidly decays in energy within 20 fs and then fluctuates until the end, providing insights into the emission mechanism of SWCNTs. This study highlights the potential intrinsic limitations of surface-functionalized SWCNTs for luminescence applications.

Ultrafast dynamics of water system under photoexcitation

<sec>Experimental techniques and theoretical calculations have made significant breakthroughs recently in realizing the ultrafast time resolution and the understanding of microscopic details on an atomic scale, which has brought new insights into the ultrafast microscopic dynamics of water system and aqueous system. Here we focus on the dynamic processes of ionization, dissociation, as well as plasmonization of water molecules, water clusters, and liquid water under different intensities of light excitation.</sec><sec>The pump-probe technique allows one to extract the information about the orbital-dependent phase shift during photoionization, corresponding to delays on a time scale from tens to hundreds of attoseconds. Delay time in photoionization is found to be proportional to the delocalization of molecular/cluster orbitals. In addition, the information related to the Feshbach resonance is also of interest. By solving the scattering equations, the detailed information about the scattering cross section, the <i>β</i>-parameter, and the involved Rydberg orbitals during valence electron ionization of water is obtained.</sec><sec>For liquid water undergoing irradiation by an optical field, the tunneling electrons are unable to move away and recombine with the parent molecule on a time scale of 100 fs if the external field is not strong enough (e.g. ~100 kV/cm). For terahertz fields as high as 250 kV/cm, electrons will move away from the parent molecule after tunnelling and undergo decoherence on a 10-fs time scale. At the beginning of tunneling the electrons will be more delocalized and will collapse to a certain position on a time scale of ~1 ps, and then slowly diffuse or recombine with holes on a longer time scale. For the strong excitation case, hot electrons may also be formed. When a hot electron is located on a particular water molecule, the O—H bond will be broken.</sec><sec>When an electron ionizes away, a hole will be created. The hole will be located on a water molecule within 10 fs, and will trigger off subsequent processes such as proton transfer and coherent oscillations. In particular, after the hole is localized and before the proton is transferred, there is a brief appearance of the metastable <inline-formula><tex-math id="M1">\begin{document}$ {{{\mathrm{H}}}_{2}{\mathrm{O}}}^{+} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240047_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240047_M1.png"/></alternatives></inline-formula> ion, whose lifetime is experimentally captured and is predicted to be (46±10) fs. The nuclear quantum effect in this process plays a key role.</sec><sec>Using the methods such as real time-time dependent density functional theory (rt-TDDFT), it is found that the water undergoes plasmonization under intense laser pulses corresponding to a field strength amplitude larger than 2.4 V/Å. The effective electron temperature in this period reaches over 20000 K. Strongly excited water in this state exhibits the behaviors of a liquid metal, and extremely strong nonthermal effect and nonadiabatic effect. In the process of plasmonization, a large fraction of chemical bonds in water molecules are broken and reorganize themselves, and many chemical species such as hydrogen molecules may appear, which also implies that laser-induced plasmonization can be used to synthesize new substances.</sec><sec>Although the previous researches have brought about a very rich understanding, we have also found some details that still need to be explored: i) the influence of nuclear quantum effects has not been taken into account in most of theoretical calculations, which may result in the inadequate description and inaccurate prediction; ii) some of the microscopic details observed in simulations do not yet have a direct counterpart in experimental measurements; iii) the current simulation of water plasmonization is for the local behavior under the spatially uniform external field, while in the real situation there are spatial inhomogeneity and energy flow, which urgently need larger-scale excited state dynamics simulations.</sec><sec>With the development of laser technology, the integration of water science and ultrafast technologies will be increasingly strong, so we believe that such a systematic understanding will play a key role in the future. It is expected that new research efforts will continue to contribute to a better understanding and the generation of new technologies in this exciting research field.</sec>

A different view on the deactivation process of 3-hydroxy-salicylidene-methylamine system

Schiff bases stand out as a highly significant class of photochromic materials with widespread applications. The exploration of their photochromic mechanisms has garnered substantial interest over the past decades. In this work, we investigated the photochromic mechanism of 3-hydroxy-salicylidene methylamine (3-OH-SMA) by high-level electronic structure calculations and on-the-fly excited state dynamics simulations. Our investigation revealed the identification of three minimum energy conical intersections between S1 and S0 states, while only the one characterized by the central C = N bond twisting motion was involved in the deactivation process. This finding contrasts with previous reports, suggesting that the excited state intramolecular proton transfer (ESIPT) process was the main reaction channel in 3-OH-SMA. The proposed new decay mechanism provides valuable theoretical insights, paving the way for the further enhancement or rational design of photochromic materials.

Vibrational Coherences of the Photoinduced Mixed-Valent Creutz-Taube Ion Revealed by Excited State Dynamics.

A recent study of photoinduced mixed-valency in the one-electron reduced form (μ-pz)[RuII(NH3)5]24+ of the Creutz-Taube ion used transient absorption spectroscopy with vis-NIR broadband detection to uncover a mixed-valent excited state with a typical intervalence charge transfer band and a nanosecond lifetime [Pieslinger et al. Angew. Chem., Int. Ed. 2022, 61, e202211747]. Herein, we use excited state dynamics simulations with implicit solvation to elucidate the electronic and vibrational evolution in the first 10 ps after the optical excitation. A manifold of excited states with weak interaction between the metal centers is populated already at time zero due to the breakdown of the Condon approximation and dominates the population of electronic states at short time scales (<0.5 ps). A long-lived vibrational wave packet mostly confined to oscillations of the metal center-bridge distances is observed. The oscillations are traced to the electronic structure properties of states with weak metal-metal coupling. The long-lived mixed-valent excited state of the Creutz-Taube ion analogue is formed vibrationally cold and has a more compact geometry. While experimentally, intersystem crossing and vibrational relaxation were deduced to be completed within 1 ps, our analysis indicates that both processes might persist at longer times.

Characterization of Type I/II g-C3N4/MoS2 van der Waals Heterostructures: A New Theoretical Insight.

The charge transfer mechanism of the g-C3N4/MoS2 heterojunction is still disputed. Some regard it as a type I pathway, some regard it as a type II pathway, and still some regard it as a Z-scheme pathway. Especially, the results obtained by density functional theory (DFT) calculations are not totally in agreement. Here, we constructed four g-C3N4/MoS2 heterojunctions on the basis of the aperture alignment modes of g-C3N4 and MoS2. Their morphology and photocatalytic activity were investigated via first-principles and excited state dynamics simulations. By systemically comparing the interfacial binding energy and electronic structure (e.g., band structure, electrostatic potential, and band edge positions) of g-C3N4/MoS2 heterojunctions, we found that both type I and type II band alignment structures could be obtained. Moreover, the calculated lifetimes of interlayer photogenerated electrons and holes show that type II g-C3N4/MoS2 tends to favor a general type II pathway rather than a Z-scheme pathway. This study could provide a deep understanding of the photocatalytic mechanism of g-C3N4/MoS2 van der Waals heterostructures, which will be of great use for applications in photocatalysis.

Theoretical Studies and Design Strategies of Highly Efficient Two-Photon Excited Fluorescent Probes for Hydrogen Sulfide Detection through Simulation of Excited-State Dynamics.

Hydrogen sulfide (H2S) plays a critical role in numerous physiological and pathological processes, but an abnormal level of H2S in living systems can cause various diseases. To detect the level of endogenous H2S in a complicated biological system, the luminous mechanism of "turn-on" probe for H2S monitoring has been deeply explored through the simulation of excited-state dynamic processes, and the effect of different geometric modifications on optical properties has been minutely investigated based on molecular modeling. TD-DFT calculations demonstrate that line-type π-expanding in the molecular skeleton is beneficial for improving two-photon absorption (TPA) ability, but it can give rise to extremely large geometric relaxation, going against fluorescence emission. It is an effective way to suppress molecular skeleton scissoring vibration by introducing strong electron-withdrawing substituent groups (F, Cl, Br, CN) in benzopyran, and these compounds also have superior TPA properties in NIR. One of the potential materials in the application of biological imaging and H2S detection has been obtained, which simultaneously possesses easily distinguished spectra (with a Stokes shift as large as 77 nm), high luminous efficiency (with a quantum yield up to 20.07%), and large TPA cross section (952 GM at 950 nm).

Excited-state molecular dynamics simulation based on variational quantum algorithms

We propose an excited-state molecular dynamics simulation method based on variational quantum algorithms at a computational cost comparable to that of ground-state simulations. We utilize the feature that excited-states can be obtained as metastable states in the restricted variational quantum eigensolver calculation with a hardware-efficient ansatz. To demonstrate the effectiveness of the method, molecular dynamics simulations are performed for the S1 excited-states of H2 and CH2NH molecules. The results are consistent with those of the exact adiabatic simulations in the S1 states, except for the CH2NH system, after crossing the conical intersection, where the proposed method causes a nonadiabatic transition.

Effects of solvent polarity on the novel excited-state intramolecular thiol proton transfer and photophysical property compared with the oxygen proton transfer

Recently, the dual-fluorescent phenomena of excited state intramolecular thiol proton transfer (ESIPT) for 3-thiolflavone derivative (3NTF) were reported by Chou and coworkers for the first time [J. Am. Chem. Soc. 143 (2021) 12715–12724], which opened a new chapter in the field of ESIPT. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT), the proton transfer processes of 3NTF in toluene, dichloromethane and acetonitrile were studied. By optimizing the structure of the ground (S0) state and first excited (S1) state of 3NTF in different solvents, the hydrogen-bond parameters and proton-transfer potential energy curves were calculated. It was shown that although photo-excitation enhanced the intramolecular hydrogen bonding strength and thus promoted the occurrence of ESIPT, the solvent polarities inhibited the enhancement of the hydrogen bond of S1 state, which was not conducive to ESIPT. The electron spectra analyses were consistent with experimental data, which confirmed the rationality of molecular configurations. The time-evolved excited state dynamics simulation was performed based on the optimized structure of 3NTF, indicating that the ESIPT was an ultrafast photochemical reaction less than 180 fs. Moreover, we compared the potential energy surfaces of ESIPT, electronic structures based on natural transition orbitals (NTOs) method and electron-hole isosurfaces for the 3NTF and the traditional flavone molecule (3NHF), concluded that the unusually large Stokes shift fluorescence of 3NTF was mainly caused by the coupling of ESIPT and twisting intramolecular charge transfer (TICT), and the 3NTF isomer had the more nπ* character in the electron transition process. The nπ* ICT significantly increased with the decrease of solvent polarities, affecting the molecular photophysical properties, this made it more widely used in biomedical, photochemical, materials science and other fields.

Extending multi-layer energy-based fragment method for excited-state calculations of large covalently bonded fragment systems.

Recently, we developed a low-scaling Multi-Layer Energy-Based Fragment (MLEBF) method for accurate excited-state calculations and nonadiabatic dynamics simulations of nonbonded fragment systems. In this work, we extend the MLEBF method to treat covalently bonded fragment ones. The main idea is cutting a target system into many fragments according to chemical properties. Fragments with dangling bonds are first saturated by chemical groups; then, saturated fragments, together with the original fragments without dangling bonds, are grouped into different layers. The accurate total energy expression is formulated with the many-body energy expansion theory, in combination with the inclusion-exclusion principle that is used to delete the contribution of chemical groups introduced to saturate dangling bonds. Specifically, in a two-layer MLEBF model, the photochemically active and inert layers are calculated with high-level and efficient electronic structure methods, respectively. Intralayer and interlayer energies can be truncated at the two- or three-body interaction level. Subsequently, through several systems, including neutral and charged covalently bonded fragment systems, we demonstrate that MLEBF can provide accurate ground- and excited-state energies and gradients. Finally, we realize the structure, conical intersection, and path optimizations by combining our MLEBF program with commercial and free packages, e.g., ASE and SciPy. These developments make MLEBF a practical and reliable tool for studying complex photochemical and photophysical processes of large nonbonded and bonded fragment systems.

Exploring the Ti2CO2–WSe2 Heterostructure as a Direct Z-Scheme Photocatalyst for Water Splitting: A Non-Adiabatic Study

One of the potential strategies to solve renewable energy shortage is to design low-cost efficient photocatalysts for water splitting to aid hydrogen and oxygen evolution reactions (HER and OER). Two-dimensional (2D) materials like MXenes and transition metal dichalcogenides (TMDs) have caught special attention owing to their unique optical, electrical, and mechanical properties, but come with issues like photocorrosion and poor charge separation. Bilayer vdW heterojunctions of suitable constitutive monolayers are coming up as a potential solution to these hazards, accredited to their tunable band gap and efficient charge separation. In this paper, we have investigated the possibility of Ti2CO2–WX2 (X = S, Se, Te) vdW heterostructures to perform as Z-scheme photocatalysts by employing first-principle density functional calculations, and thereby, the Ti2CO–WSe2 heterostructure has emerged as the most promising material for Z-scheme photocatalysis. Further, excited-state dynamics simulation reveals that the timescales of electron transfer and hole transfer are greater (1.13 and 1.22 ps, respectively) than the maximum time limit of the photogenerated electron–hole recombination (1.0 ps) owing to the weaker non-adiabatic coupling and electron–phonon coupling. This affirms the fact that photogenerated electrons and holes with greater redox ability are preserved to drive the photocatalytic pathway. In addition to that, the free energy calculations associated with the HER and OER processes entail that the processes occur spontaneously on the surface of the heterostructure without any co-catalyst. This establishes the Ti2CO–WSe2 heterostructure as a potential mediator-free direct Z-scheme photocatalyst for overall water splitting.

Machine learning the Hohenberg-Kohn map for molecular excited states

The Hohenberg-Kohn theorem of density-functional theory establishes the existence of a bijection between the ground-state electron density and the external potential of a many-body system. This guarantees a one-to-one map from the electron density to all observables of interest including electronic excited-state energies. Time-Dependent Density-Functional Theory (TDDFT) provides one framework to resolve this map; however, the approximations inherent in practical TDDFT calculations, together with their computational expense, motivate finding a cheaper, more direct map for electronic excitations. Here, we show that determining density and energy functionals via machine learning allows the equations of TDDFT to be bypassed. The framework we introduce is used to perform the first excited-state molecular dynamics simulations with a machine-learned functional on malonaldehyde and correctly capture the kinetics of its excited-state intramolecular proton transfer, allowing insight into how mechanical constraints can be used to control the proton transfer reaction in this molecule. This development opens the door to using machine-learned functionals for highly efficient excited-state dynamics simulations.

Revealing and Tuning the Photophysics of C=N Containing Photothermal Molecules: Excited State Dynamics Simulations.

Molecular photothermal conversion materials are recently attracting increasing attention for phototherapy applications. Herein we investigate the excitation and de-excitation processes of a photothermal molecule (C1TI) that is among the recently developed class of small-molecule-based photothermal imines with superb photothermal conversion efficiencies (PTCEs) up to 90% and a molecule (M2) that is constructed by replacing the amino group of C1TI with an H atom, via excited-state dynamics simulations based on the time-dependent density functional theory (TD-DFT). The simulations reveal fast (<150 fs of average time) nonradiative decays of the lowest excited singlet (S1) state to a conical intersection (CI) with the ground (S0) state in high yields (C1TI: 93.9% and M2: 87.1%). The fast decays, driven by C=N bond rotation to a perpendicular structural configuration, are found to be barrierless. The slight structural difference between C1TI and M2 leads to drastically different S0-S1 energy surfaces, especially M2 features a relatively much lower CI (0.8 eV in energy) and much more decay energy (1.0 eV) to approach the CI. This work provides insights into the de-excitation mechanisms and the performance tuning of C=N enabled photothermal materials.

Adiabatic Excited-State Molecular Dynamics with an Explicit Solvent: NEXMD-SANDER Implementation.

We present a method to link the Nonadiabatic EXcited-state Molecular Dynamics (NEXMD) package to the SANDER package supplied by AMBERTOOLS to provide excited-state adiabatic quantum mechanics/molecular mechanics (QM/MM) simulations. NEXMD is a computational package particularly developed to perform simulations of the photoexcitation and subsequent nonadiabatic electronic and vibrational energy relaxation in large multichromophoric conjugated molecules involving several coupled electronic excited states. The NEXMD-SANDER exchange has been optimized in order to achieve excited-state adiabatic dynamics simulations of large conjugated materials in a QM/MM environment, such as an explicit solvent. Dynamics of a substituted polyphenylene vinylene oligomer (PPV3-NO2) in vacuum and different explicit solvents has been used as a test case by performing comparative analysis of changes in its optical spectrum, state-dependent conformational changes, and quantum bond orderings. The method has been tested and compared with respect to previous implicit solvent implementations. Also, the impact on the expansion of the QM region by including a variable number of solvent molecules has been analyzed. Altogether, these results encourage future implementations of NEXMD simulations using the same combination of methods.

Theoretical investigation on the fluorescent sensing mechanism for recognizing formaldehyde: TDDFT calculation and excited-state nonadiabatic dynamics

Inspired by the activity-based sensing method, the hydrazine-modified naphthalene derivative (Naph1) was synthesized and used as a fluorescent probe to detect formaldehyde (FA) in living cells. Through the condensation reaction between the probe Naph1 and analyte FA, researchers observed a ∼14 folds enhancement of fluorescent signal around 510 nm in an experiment, realizing the high selectivity and sensitivity detection of FA. However, a theoretical understanding of the sensing mechanism was not provided in the experimental work. Given this, the light-up fluorescent detecting mechanism was in-depth unveiled by performing the time-dependent density functional theory (TDDFT) and the complete active space self-consistent field (CASSCF) theoretical calculations on excited-state intramolecular proton transfer (ESIPT) and non-adiabatic excited-state dynamics simulation. The deactivation channel of S1/T2 intersystem crossing (ISC) was turned off to successfully recognize FA. Insight into the ESIPT-based fluorescent detecting mechanism indicated that ESIPT was essential to light-up fluorescent probes. This work would provide a new viewpoint to develop ESIPT-based fluorescent probes for detecting reactive carbon species in vivo or vitio.

New insights into the excited state intramolecular proton transfer (ESIPT) competition mechanism for different intramolecular hydrogen bonds of Kaempferol and Quercetin in solution

In this work, the process of the Excited State Intramolecular Proton Transfer (ESIPT) competition of Kaempferol and Quercetin in methanol was studied by means of the Density Functional Theory (DFT) and the Time-Dependent Density Functional Theory (TDDFT) method. Two different ESIPT reaction pathways were analyzed by the variation trend of the 3D potential energy surfaces (PESs) with the change of the intramolecular hydroxyl bond length through the PESs of the two molecules of the ground state (S0) and the first excited (S1) state. The ESIPT process only occurred between O25–H28 and O22–H28 and was completed within 33.1fs by molecular excited state dynamics simulation. It is demonstrated that when there are two kinds of hydrogen bonds in the molecule, the ESIPT prefers the six-membered ring hydrogen bonds to the five-membered ring hydrogen bonds.