Single Proton Transfer Research Articles

Relationship between antioxidant activity and ESIPT process based on flavonoid derivatives: A comprehensive analysis

Antioxidant activity, as a topic of current interest, is discussed together with the excited state intramolecular proton transfer (ESIPT) process for three flavonoid derivatives, based on density functional theory (DFT)and time-dependent DFT (TD-DFT) methods, as well as DPPH free radical scavenging assay. The potential energy curves and transition states demonstrate that the three molecules can undergo only single proton transfer in the excited state, and all of them are ultrafast ESIPT processes. The absorption spectra of all the molecules show effective protection against UV radiation with low fluorescence intensity, especially Baicalein (Bai), which demonstrates their great potential for sunscreen applications. The density of states, HOMO energy values, global and local indices reveal that the antioxidant activity of the molecules after ESIPT process is enhanced, with Bai having the highest antioxidant activity, which is significantly attributed to the number and position of phenolic hydroxyl groups. Moreover, by comparing the DPPH free radical scavenging activity under the dark and UV radiation conditions, the radical scavenging activity (RSA) value in the UV radiation is remarkably higher than that in the dark condition, in which Bai achieves RSA value of 93.4%. Overall, the antioxidant activity of all three ESIPT-based flavonoid derivatives, especially Bai, is significantly elevated in the keto* form, which reinforces the significant relationship between antioxidant activity and ESIPT process, and provides new application prospects for molecules with ESIPT properties.

Unidirectional photoisomerisation in a dual channel proton transfer molecule rhodamine B based Schiff Base: A ratiometric pH sensor

In this article we have presented the synthesis, characterisation and spectral study of a newly designed fluorophore, (E)-2-((3-(benzo[d]oxazol-2-yl)-5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro [isoindoline-1,9′-xanthen]-3-one (RHHBO) which has two possible six member intramolecular hydrogen bonded networks capable for dual channels proton transfer reaction − one towards the N atom of oxazole moiety and the other towards the N atom of rhodamine moity. Details steady state and time resolved spectral analysis of RHHBO and a comparison of spectral features of control compounds 2-(2-hydroxyphenyl)benzoxazole (HBO), (E)-4-bromo-2-(hydrazonomethyl)phenol (HBN) and (E)-2-((5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (RH) having only single proton transfer site reveal that excited state intramolecular proton transfer (ESIPT) in RHHBO occurs towards the rhodamine side but not towards the oxazole side. Interestingly, RHHBO shows different fluorescence colour in acidic and basic medium and hence can be used ratiometric emission based pH sensor.

Excited-State Intramolecular Proton Transfer toward Conical Intersections in Indigo, Epindolidione, and Indirubin.

Indigo exhibits a high degree of photostability, experimentally supported by observations such as quenching of fluorescence and an exceptionally short excited-state lifetime. Epindolidione, a structural isomer of indigo, is highly fluorescent in contrast to indigo, while indirubin, another structural isomer, exhibits weak fluorescence similar to that of indigo. To elucidate the origin of the difference in photophysical and photochemical behavior, potential energy profiles of the excited-state intramolecular proton transfer in indigo, epindolidione, and indirubin are computationally studied by quantum chemical calculations using the TDDFT and extended MS-CASPT2 (XMS-CASPT2) methods. As a result, it is found that indigo and indirubin exhibit little energy barrier for the single proton transfer (SPT) in the S1(ππ*) state from the diketo to keto-enol form and low energy of the S1/S0 conical intersection (CI) in the latter form with a planar molecular structure. Epindolidione, on the other hand, exhibits much higher barriers for SPT and access to CI. These results suggest that the excited-state SPT and subsequent nonradiative deactivation via CI are more likely to occur in indigo and indirubin than in epindolidione, which is consistent with the experimental observations described above. For indigo and epindolidione, the deactivation channels via the second SPT from the keto-enol to dienol form are also compared.

Theoretical Study on Optoelectronic Properties of 1,4-Dithiazole-5,10-dihydrophenazine and Its B ← N-Fused Derivatives.

Recently, Liu et al. reported 1,4-dithiazole-5,10-dihydrophenazine (DTDHP) and its B ← N-fused derivative (DTHDHP-BF2), which were expected to show excellent optoelectronic properties (Angew. Chem. Int. Ed. 2022, 61, e202205893). However, their charge-transport performance and luminescence emission mechanisms have not been revealed. In this work, we used density functional theory (DFT) calculations to investigate the optoelectronic properties of DTDHP and DTHDHP-BF2 and analyzed the influence of the introduction of -BF2 on the basic parameters governing charge transport and injection in detail. Our calculation results showed that adding -BF2 could stabilize the frontier molecular orbitals and decrease the reorganization energies associated with electron transport due to the formation of B ← N bonds, and the intermolecular electronic couplings are greatly enhanced owing to the strong intermolecular F···H interactions. Based on the master equation coupled with the Marcus-Hush electron transfer theory, we theoretically predicted the charge transport properties of DTDHP and DTHDHP-BF2. The optimum hole mobility (3.87 cm2 V-1 S-1) and electron mobility (1.52 cm2 V-1 S-1) of DTHDHP-BF2 are, respectively, 3 and 9 times as high as the corresponding optimum values of compound DTDHP. Moreover, the assignments of multiple fluorescence bands in the experiment were confirmed by time-dependent density functional theory (TDDFT) calculations. The simulated emission spectra indicate that the experimental fluorescence maxima at 687 nm originates from the S1 → S0 transition of the double proton transfer phototautomer (T2H) of DTDHP, and the shoulder peak at ∼660 nm may be related to the excited-state single-proton transfer phototautomer (T1H); for DTHDHP-BF2, the experimental fluorescence maxima at 687 nm should be attributed to normal Stokes shifted emission, and the shifted fluorescence with a peak at 751 nm originates from the emission of the photodissociation product of DTHDHP-BF2.

Tactfully regulating the ESIPT and TICT mechanism in the AIE-active multifunctional triphenylamine Schiff-base compound (TPASB) by methyl substitution

The triphenylamine Schiff-base (TPASB) with dual proton transfer sites (N1…H1–O1 [R1] and N2…H2–O2 [R2]), which is crucial in the field of optoelectronic materials. Herein, a novel molecular design strategy for preparing of TPASB-1 and TPASB-2 via the selective methylation of the hydroxyl group at the R2 or R1 position was proposed. The analysis of electronic structures and potential energy surfaces revealed that a single excited state intramolecular proton transfer (ESIPT) process of TPASB occurs only at R1. Nevertheless, the ESIPT process of TPASB-2 was successfully turned on at R2. More noteworthy is that compared to TPASB, the methylation of hydroxyl group at the R2 position triggers the TICT process of TPASB-1, effectively reducing the potential barrier of ESIPT at the R1 position. This theoretical study explains the role of the substituent effect in regulating ESIPT behaviour, and provides valuable guidance for synthesising efficacious ESIPT-active compounds.

Highly Stable Red Emissive Organic Semiconductor Materials with Low Amplified Spontaneous Emission Thresholds

AbstractExcited‐state intramolecular proton transfer (ESIPT) chromophores have attracted considerable attention as promising gain media for organic lasers, particularly in amplified spontaneous emission (ASE) due to their advantageous characteristics. These include an intrinsic four‐level photocycle, significant separation between absorption and emission spectra, and enhanced emission efficiency facilitated by aggregate‐induced emission. This study investigates the amplification of π‐conjugation in hydroxyphenyl‐benzothiazole (HBT)‐based ESIPT materials via dimerization to intensify ESIPT processes, surge absorption cross‐section, enhance optical gain, and induce a redshift in emission spectra. Computational study shows that the ESIPT processes of the new dimers proceed through single proton transfer where the second proton transfer is not accessible. While the ESIPT photocycle does not extend to both HBT moieties of the dimers, the dimers foster more efficient ESIPT processes in both solution and solid states than their parent HBT, resulting in substantial Stokes shifts (>233 nm). Moreover, both dimers exhibit enhanced solid‐state photoluminescence quantum yields, reaching up to ≈55%, and low solid‐state ASE threshold values (≈6.8 µJ cm−2) in the red region. Remarkably, the new dimers demonstrate excellent thermal and photostability with notably reduced spectral overlap compared to their parent, highlighting the potential utility of the approaches to developing new organic solid‐state laser materials.

Proton Transfer via Arginine with Suppressed pKa Mediates Catalysis by Gentisate and Salicylate Dioxygenase.

Gentisate and salicylate 1,2-dioxygenases (GDO and SDO) facilitate aerobic degradation of aromatic rings by inserting both atoms of dioxygen into their substrates, thereby participating in global carbon cycling. The role of acid-base catalysts in the reaction cycles of these enzymes is debatable. We present evidence of the participation of a proton shuffler during catalysis by GDO and SDO. The pH dependence of Michaelis-Menten parameters demonstrates that a single proton transfer is mandatory for the catalysis. Measurements at variable temperatures and pHs were used to determine the standard enthalpy of ionization (ΔHion°) of 51 kJ/mol for the proton transfer event. Although the observed apparent pKa in the range of 6.0-7.0 for substrates of both enzymes is highly suggestive of a histidine residue, ΔHion° establishes an arginine residue as the likely proton source, providing phylogenetic relevance for this strictly conserved residue in the GDO family. We propose that the atypical 3-histidine ferrous binding scaffold of GDOs contributes to the suppression of arginine pKa and provides support for this argument by employing a 2-histidine-1-carboxylate variant of the enzyme that exhibits elevated pKa. A reaction mechanism considering the role of the proton source in stabilizing key reaction intermediates is proposed.

Stepwise Excited-State Intramolecular Double Proton Transfer in 1,8-Dihydroxynaphthalene-2,7-dicarbaldehyde.

We theoretically investigate the salient features of stepwise excited-state intramolecular double proton transfer (ESIDPT) in 1,8-dihydroxynaphthalene-2,7-dicarbaldehyde (DHDA). Surface trajectory simulations using the TD-B3LYP/6-31G(d) level of theory reveal that the proton transfer primarily happens via S1, wherein about ∼42% of trajectories (40 out of 95) show the single proton transfer alone and another ∼32% (30 out of 95) show double proton transfer. The average time scale for the single proton transfer originating from those ∼42% trajectories is ∼147 fs. In the case of double proton transfer, the average time for the first step, i.e., single proton transfer, is ∼54 fs, and the subsequent step, i.e., double proton transfer, completes in ∼151 fs. All three tautomers, i.e., normal, single, and double proton-transferred tautomers, possess a stable minimum in their first singlet excited state. This state has a ππ* character in the former two tautomers, resulting in a dual fluorescence emission phenomenon upon photoexcitation of DHDA.

Ultrafast excited state intramolecular proton transfer and isomerization of long-chain linked Schiff bases.

The ultrafast proton transfer and the following dynamics for aromatic Schiff bases N,N'-bis(salicylidene)ethylenediamine (salen) and N,N'-bis(salicylidene)-1,4-butylenediamine (salbn) were investigated with experimental and theoretical methods. A dual emission property with a large Stokes shift in salen and salbn indicates that excited state intramolecular proton transfer occurs with photoexcitation. An efficient single proton transfer was confirmed within 200fs for both molecules. Subsequently, a fast twisted motion of the keto moiety carries cis-keto to a relaxed stable geometry in the S1 state. Following the twisted motion, the phenol ring at keto moiety further rotates to a conical intersection with the ground state and a cis-trans isomerization occurs. The isomerization rate is high, which dominates the competition with the radiative transition, resulting in weak emission intensity. It is confirmed that the length of alkyl chain affects the direction of phenol ring twisting and rotation during the whole subsequent relaxation of excited cis-keto tautomer. Compared with polar solvent acetonitrile, the barrier of isomerization is higher and the hydrogen bond on keto moiety is stronger in nonpolar solvent toluene. It makes fluorescence radiation channels competing with isomerism more likely to occur, contributing to the observed difference of enol/keto emission ratios of salen and salbn in toluene and acetonitrile.

A thermochromic salicylaldehyde Schiff bases derivative with AIE properties due to twisted structure

Great attention has been attracted to the salicylaldehyde Schiff base due to its thermochromic and photochromic characteristics in the solid state. However, the boundary between photochromic and thermochromic salicylaldehyde Schiff base structures is still unclear, and few studies have been conducted to investigate their thermochromic behavior and structures in depth and systematically. In the present work, we have synthesized a novel salicylaldehyde Schiff base derivative (2,2′-((1E,1′E)-((2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)-bis(azaneylylidene))bis(methaneylylidene))diphenol, BTB) with twisted structure, which possesses both thermochromic and aggregation-induced emission (AIE) characteristics, and systematically investigated its thermochromic properties, enol-keto isomerization, AIE properties, aggregated state, and excited state intramolecular proton transfer (ESIPT) process. Interestingly, in our study, we found that the color of the BTB molecule changed gradually during the heating process, and it can be found that the thermochromism of BTB is produced by the reversible equilibrium shift of the enol form and the keto forms due to the temperature change by the color difference test, the in-situ IR spectra and the DSC curves. Finally, the pathway of BTB proton transfer was analyzed through quantum chemical calculations, and it was found that enol ketone isomerization is achieved through single excited state intramolecular proton transfer, rather than the expected double excited state intramolecular proton transfer.

Spectral, crystal structure of novel Pyran-2-one Zwitterion Schiff derivative: Thermal, Physicochemical, DFT/HSA-interactions, enol↔imine tautomerization and anticancer activity

A novel Schiff base (SB) derivative, (E)-3-(1-((2,6-diisopropylphenyl)-imino)-ethyl)-4‑hydroxy-6-methyl-2H-pyran-2-one, was synthesized in a high yield through the direct condensation of 2,6-diisopropylaniline with 3-acetyl-4‑hydroxy-6-methyl-2H-pyran-2-one in ethanol under reflux conditions. The synthesized ligand was identified using different elemental analysis (CHN-EA) and spectroscopic techniques (2D-nuclear magnetic resonance (1H- & 13C- NMR), Fourier transform infrared (FT-IR) and mass (MS) spectroscopies), and their structural analysis was performed by single crystal X-ray diffraction (XRD). In addition, the thermogravimetric behavior of the ligand was evaluated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The DFT calculations on the gaseous state and in chloroform as solvent using B3LYP-D3/6–311++G(2d,p) and the HSA calculations were performed to examine the stability of the tautomeric forms of the ligand and to understand its Zwitterionic behaviors. The results showed that the ligand exhibits a zwitterionic form stabilized by an intramolecular single proton transfer process between the enol and imine tautomerism. The enol↔imine tautomerization was determined by XRD and computed by DFT/HSA calculations, which proved the stabilization of the [N+−−H⋯O−−] zwitterionic form via S6 intra-H-bond. In addition, the Colorimetric [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that the ligand exhibits high activity against cancer cells, specifically HeLa cells, at low concentrations.

Photochemical Mechanisms of Hydroxyquinoline Benzimidazole: Insights from Electronic Structure Calculations and Nonadiabatic Dynamics Simulations.

Excited-state intramolecular double proton transfer (ESIDPT) has received much attention because of its widespread existence in the life reactions of living organisms, and materials with this property are significant for their special luminescent properties. In this work, the complete active space self-consistent field (CASSCF) and OM2/multireference configuration interaction (OM2/MRCI) methods have been employed to study the static electronic structure calculations of the photochemistry and the possibility of ESIDPT process of hydroxyquinoline benzimidazole (HQB) molecule, along with the nonadiabatic dynamics simulations. The computational results show that the HQB molecule is relaxed to the S1-ENOL minimum after being excited to the Franck-Condon point in the S1 state. Subsequently, during the nonadiabatic deactivation process, the OH···N proton transfer and the twisting of benzimidazole occur before arriving at the single proton transfer conical intersection S1S0-KETO. Finally, the system can either return to the initial ground-state structure S0-ENOL or to the single proton transfer ground-state structure S0-KETO, both of which have almost the same probability. The dynamics simulations also show that no double proton transfer occurs. The excited-state lifetime of HQB is fitted to 1.1 ps, and only 64% of the dynamic trajectories return to the ground state within the 2.0 ps simulation time. We hope the detailed reaction mechanism of the HQB molecule will provide new insights into similar systems.

Nuclear Quantum Effects in Proton or Hydrogen Transfer.

Proton or hydrogen transfers, basic chemical reactions, proceed either by thermally activated barrier crossing or via tunneling. Studies of molecules undergoing single or double proton or hydrogen transfer in the ground or excited electronic state reveal that tunneling can dominate under conditions usually considered to favor the thermal process. Moreover, the tunneling probability strongly varies for excitation of certain vibrational modes, which changes the effective barrier and/or proton transfer distance. When the reaction is fast compared to vibrational relaxation, the mode selectivity can still be maintained for molecules in solutions at 293 K. These observations point to dangers of relating the calculated minimum energy paths and the associated barriers to the experimentally obtained activation energies. The multidimensional character of the reaction coordinate is obvious; it can dramatically change for slowly and rapidly relaxing environments. We postulate that the hydrogen bond definition should be extended by specifically including the role of molecular vibrations.

Propagating multi-dimensional density operators using the multi-layer-ρ multi-configurational time-dependent Hartree method

Solving the Liouville–von-Neumann equation using a density operator provides a more complete picture of dynamical quantum phenomena than by using a wavepacket and solving the Schrödinger equation. As density operators are not restricted to the description of pure states, they can treat both thermalized and open systems. In practice, however, they are rarely used to study molecular systems as the computational resources required are even more prohibitive than those needed for wavepacket dynamics. In this paper, we demonstrate the potential utility of a scheme based on the powerful multi-layer multi-configurational time-dependent Hartree algorithm for propagating multi-dimensional density operators. Studies of two systems using this method are presented at a range of temperatures and including up to 13 degrees of freedom. The first case is single proton transfer in salicylaldimine, while the second is double proton transfer in porphycene. A comparison is also made with the approach of using stochastic wavepackets.

Proton coupled isomerization in double-hydrogen-bonding-center salicylaldehyde azine

The proton transfer dynamics of Schiff bases are of great importance due to the application potential. The excited state intramolecular proton transfer (ESIPT) of photochromic salicylaldehyde azine (SAA) in solutions was investigated by experimental and computational methods. Two distinguished spectral bands are observed in transient absorption spectra upon the photoexcitation with 400 nm. From the delayed stimulated emission signals, the ESIPT process is determined to be within <200 fs. Subsequently, the photoprotonated products undergo the vibrational relaxation with several picoseconds and the following isomerization with tens of picoseconds. These processes are significantly affected by the polarity of the solvents. The longest component with nanosecond scale can be explained to the relaxation to the enol structure. According to our observations, the SAA molecules with symmetric double-hydrogen-bonding-centers undergo single proton transfer rather than double proton transfer and subsequent intramolecular isomerization.

Probing the water mediated proton transfer in histidine tautomerization

Histidine tautomerism plays a key role in the aggregation of amyloid peptides, which is important for understanding the origin of Alzheimer’s disease as well as its diagnosis and treatment. Herein, density functional theory calculations were performed using explicit water molecules and joint implicit/explicit water cluster models to explore the catalytic mechanism and the key role of water assistance effect in the histidine tautomerization reaction. To clarify the proton transfer mechanism involved in histidine tautomerization, three to five water molecules were used to catalyze the proton transfer process governing the transition between the histidine tautomers. Potential energy calculations showed that hiε·(H2O)n tautomerism proceeds via a single proton transfer pathway. Systematic analyses of the hydrogen bonds and charge distribution of the key components indicated that tautomerism can be promoted by reducing the number of assistant water molecules or involving the joint implicit/explicit water solvent effect. This study provides theoretical insights into the mechanism of water-assisted histidine isomerization as it relates to the Aβ aggregation hypothesis of Alzheimer’s disease.

Time-resolved fluorescence spectroscopy for studying stepwise excited-state intramolecular double proton transfer

Nowadays, single excited-state intramolecular proton transfer (ESIPT) is well studied and widely reported. However, excited-state multiple intramolecular proton transfer has not been thoroughly researched until the past decade. And now there is an increasing scientific interest not only in single but also in multiple ESIPT processes occurred in various molecules, because it offers great opportunities to apply such compounds in chemical sensors, molecular switches, NIR emitting devices and liquid crystals with high fluorescence. A stepwise excited-state intramolecular double proton transfer (ESIDPT) is among such multiple ESIPT processes. Similar to the single ESIPT, stepwise ESIDPT also occurs via an intramolecular hydrogen bonding way. But in the stepwise ESIDPT, two proton transfers occur sequentially in a molecule, because there is only one proton transfer site in the initial molecular structure. Then, after the first ESIPT, an additional proton transfer site appears, and the second proton transfer will occur.In this work, an emission of stepwise ESIDPT-active molecules was studied from the point of view of a time-resolved fluorescence spectroscopy. The theoretical model for emission decay was discussed on the basis of a six states model. This model consists of three pairs of ground and excited states for normal molecular form and two tautomers. It leads to three-exponential equations for emission decay functions. It was shown that a thorough analysis of fluorescence decay curves allows to estimate the total decay rate constants for each excited molecular form. The proposed model has been validated for a numerically simulated case. The experimental data have also been discussed from the point of view of the proposed model.

Fluorescent deactivation behaviors based on ESIPT and TICT of novel double target fluorescent probe and its sensing mechanism for Al3+/Mg2+: A TD-DFT study

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods with integral equation formula polarized continuum model (IEFPCM), the fluorescent behavior and recognizing mechanism of probe N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI) for Al3+/Mg2+ ion were investigated in more detail. Excited state intramolecular proton transfer (ESIPT) process in probe NHMI occurs in the stepwise pattern. The proton H5 of enol structure (E1) firstly moves from O4 to N6 to form single proton-transfer (SPT2) structure, and then the proton H2 of SPT2 transfers from N1 to N3 to form the stable double proton-transfer (DPT) structure. Subsequently, the transformation from DPT to its isomer (DPT1) induces the twisted intramolecular charge transfer (TICT) process. Two non-emissive TICT states (TICT1 and TICT2) were obtained, and TICT2 state quenches the fluorescence observed in the experiment. With the addition of aluminum (Al3+) or magnesium (Mg2+) ion, TICT process is prohibited by the coordination interaction between NHMI and Al3+/Mg2+, and the strong fluorescent signal is turned on. For probe NHMI, the twisted C-N single bond of acylhydrazone part leads to the TICT state. This sensing mechanism may inspire researchers to develop new probes from a different direction.

Elution-extrusion counter-current chromatographic separation and theoretical mechanism of antioxidant from Robinia pseudoacacia flower.

Robinia pseudoacacia flowers have attracted much attention because of numerous bioactivities. In this study, its extract showed the potential scavenging ability for 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) and 1,1-diphenyl-2-picrylhydrazyl free radicals. Under the guidance of antioxidant activity, the antioxidant extract was enriched by liquid-liquid extraction. The partition coefficients of the two main components in antioxidant extracts differed greatly, so in this study, elution-extrusion counter-current chromatography with the solvent system of n-hexane-ethyl acetate-methanol-water (2.5:5:2.5:5, v/v) was used to enhance the separation efficiency, and the two main components were successfully obtained. Among them, kaempferol showed strong antioxidant activity, which can be responsible for the activity of the extract. In order to deeply understand the antioxidant mechanism of kaempferol, the thermodynamics, frontier molecular orbital, and kinetics of scavenging free radicals were investigated by density functional theory. The results showed that 4'-OH in kaempferol was the most active group, which can scavenge free radicals by hydrogen atom transfer in non-polar solvents and activate 3-OH to generate double hydrogen atom transfer in the gas phase. But in polar solvents, it was more inclined to clear radicals through single electron transfer and proton transfer. The kinetic result showed that kaempferol needed 9.17kcal/mol of activation energy to scavenge free radicals.

Theoretical insights into the excited-state single and double proton transfer processes of DEASH in water

Recently, a new fluorescent chromophore 6,6′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(3-(diethylamino)phenol) (DEASH) with double intramolecular hydrogen bonds (IHBs) was synthesized and could be used as an effective indicator of hydrazine. The experimental results showed that DEASH could emit bright green fluorescence due to the excited state intramolecular proton transfer (ESIPT) induced by IHBs. [Dyes Pigments, 2022, 197, 109880.] However, the underlying mechanism of the ESIPT process for DEASH is still unclear. In this paper, we investigate excited-state intramolecular single (ESISPT) and double (ESIDPT) proton transfer processes of DEASH by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Through the theoretical analyses for the constructed potential energy surfaces (PESs), excited hydrogen bond strengthening and photophysical properties of the molecule, we finally come to the conclusion that ESIDPT process of the DEASH in water solution is inclined to a stepwise process.