Bond Critical Points Research Articles

Dissolution mechanism of cellulose in a benzyltriethylammonium/urea deep eutectic solvent (DES): DFT-quantum modeling, molecular dynamics and experimental investigation.

In this paper, a benzyltriethylammonium/urea DES was investigated as a new green and eco-friendly medium for the progress of organic chemical reactions, particularly the dissolution and the functionalization of cellulose. In this regard, the viscosity-average molecular weight of cellulose (M̄w) during the dissolution/regeneration process was investigated, showing no significant degradation of the polymer chains. Moreover, X-ray diffraction patterns indicated that the cellulose dissolution process in the BTEAB/urea DES decreased the crystallinity index from 87% to 75%, and there was no effect on type I cellulose polymorphism. However, a drastic impact of the cosolvents (water and DMSO) on the melting point of the DES was observed. Besides, to understand the evolution of cellulose-DES interactions, the formation mechanism of the system was studied in terms of H-bond density and radial distribution function (RDF) using molecular dynamics modeling. Furthermore, density functional theory (DFT) was used to evaluate the topological characteristics of the polymeric system such as potential energy density (PED), laplacian electron density (LED), energy density, and kinetic energy density (KED) at bond critical points (BCPs) between the cellulose and the DES. The quantum theory of atoms in molecules (AIM), Bader's quantum theory (BQT), and reduced density gradient (RDG) scatter plots have been exploited to estimate and locate non-covalent interactions (NCIs). The results revealed that the dissolution process is attributed to the physical interactions, mainly the strong H-bond interactions.

NLO ACTIVITY AND COMPUTATIONAL DISCUSSION OF HALOGEN-SUBSTITUTED CHALCONE DERIVATIVES

The four halogen-substituted chalcones 1–4 have been synthesized and analyzed to FT-Infrared, UV-Visible, GC-MS spectrometer, and 1D NMR (1H and 13C) spectroscopy techniques. Computational calculations were carried out for geometrical optimization of structure regards bond length, bond angle, and torsional angle estimated. The molecular properties of donor-acceptor electron delocalization (NBO), Electron density, and bond critical point are carryover in (AIM), the polar site of molecules is determined by (MEP), HOMO-LUMO, and the dipole moment was calculated by GAUSSUION-09 Package. The polarizability and first-order hyperpolarizability calculations derived from non-linear optical (NLO) properties for the synthesized compounds (1-4). The disc diffusion method was used to investigate the microbial activity of antibacterial and antifungal activity.

Novel Carbene Hydroxymethylene Derivatives: Gibbs free energy, NBO, AIM, and Hammett approaches via DFT and MP2 methods

Density functional theory (DFT) and the Møller-Plesset expansion (MP2) calculations were benchmarked to characterize the structure of novel derivatives of carbene hydroxymethylene. In this regard, eleven numbers of primary aldehydes including formaldehyde, acetaldehyde, formyl chloride, 2-chloroacetaldehyde, formyl fluoride, 2-fluoroacetaldehyde, formic acid, propionaldehyde, glyoxal, methyl formate, and formyl bromide (1H-11Br) were scrutinized, at the B3LYP/6-311++G(3d,3p) level of theory. Thereafter, the process of keto-enol tautomerism via a [1,2]-H-shift of 1H-11Br was monitored to reach their corresponding enol forms (1P-11P). For all species (except for one structure), the TS involves a triangle structure of C-O-H and yields cis or trans isomers of a singlet ground-state (S) carbene that contrasts the multiplicity of ordinary carbenes. The bond dissociation energy (BDE) calculations were carried out for the homolytic cleavage of C−H bonds of 1H-11Br. The AIM, as a promising analysis that definitely reveals the nature of the bond, was conducted to characterize the eigenvalues at the bond critical points (BCPs). In addition, the relation between the Hammett equation and thermodynamic parameters was obtained. Our investigation suggests new stable S derivatives of carbene hydroxymethylene that can be isolated.

Heterobimetallic 21,23-dimetallaporphyrin: activation of metal-metal interactions within the porphyrinoid macrocycle.

Two core-modified porphyrins containing metal atoms, namely platinum(II) or platinum(IV) and rhodium(III), in place of two NH units, have been obtained by a post-synthetic modification of the 21,23-ditelluraporphyrin. The products of the tellurium-to-metal exchange, 21-platina-23-rhodaporphyrins, incorporate rhodacyclopentadiene and platinacyclopentadiene units with the metal atoms facing each other. The two molecules exhibit different degrees of metal-metal interaction depending on the oxidation state of platinum, with the NBO bond order being 0.04 for platinum(IV) and 0.15 for platinum(II). Consistently, the Quantum Theory of Atoms in Molecules analysis revealed the presence of the bond determinant, the bond critical point, in the platinum(II) species, in contrast to the platinum(IV) congener. The two porphyrinoids are interconvertible in redox reactions. They both exhibit fluxional behaviour in solution, studied by 1H NMR, involving alteration in the metal ion coordination sphere accompanied by the macrocyclic skeleton conformation change.

DFT studies of camptothecins cytotoxicity IV — active and inactive forms of irinotecan

Abstract Structures of irinotecan (CPT-11) in neutral lactone, neutral carboxyl, and anionic carboxylate forms in singlet ground states and of their complexes with Cu(II) in doublet ground states are optimized using B3LYP/6-311G* treatment. Metal ion affinities (MIA), Cu charges and Laplacians of Cu-ligand bond critical points of possible CPT active sites are evaluated. The formation of Cu(II) complexes with the anionic carboxylate ligand leads to the release of CO2 that can cause a decrease in the concentration of the active lactone form due to equilibria between all forms of the drug. MIA values and electron density transfer to Cu increase in the sequence lactone < neutral carboxyl < anionic carboxylate. Both neutral forms of irinotecan exhibit lower MIA values than those of camptothecin, unlike the anionic carboxylate form.

On the nature of noble gas - metal bond in silver aggregates.

The aim of this paper is to extend the study of the nature of the bond between noble gas to nano- and sub nanoscale silver aggregates. In the framework of DFT-PAW calculations implemented in the abinit package, we carried out a thorough investigation on the nature of the bond between the six noble gases NG (He, Ne, Ar, Kr, Xe and Rn) and numerous neutral silver aggregates Agn from the single atom Ag1 to the nanoparticle Ag147 using atoms-in-molecules (AIM) dual functional analysis,. We evaluated the impact of the silver aggregate size, the adsorption site and of the noble gas on the Ag-NG bond. Our study concluded on the favored adsorption of heavier noble gases (Kr, Xe and Rn) over that of lighter noble gases (He, Ne and Ar) on any aggregate size due to an enhanced chemical contribution in the bond. For these heavier noble gases, in accordance with studies carried out on surfaces, we noted their preferential adsorption on on-top sites rather than on hollow sites, which further evidences the chemical contribution to the bond. Moreover, the slight positive Bader charge on these heavier noble gases implies an electron transfer from the noble gas to the silver atom. Noble gas adsorption is favored on smaller, few-atom, two-dimensional clusters rather than on larger three-dimensional nanoparticles. Finally, we identified a universal power law with a unique exponent linking bond length and electronic density at the bond critical point for all aggregate sizes, noble gases and adsorption sites.

Iodine(I)-based and iodine(III)-based halogen bond catalysis on the Friedel-Crafts reaction: a theoretical study.

Halogen bond catalysis, especially iodine derivatives catalysis, has attracted increasing attention in recent years owing to the advantages of relatively cheap, stable, green, easy to handle, and favorable catalytic activity. To obtain insights into the catalytic mechanism and activity of halogen bond donor catalysts, iodine(I)-based and iodine(III)-based halogen bond catalysis on the Friedel-Crafts reaction were investigated in this study. The entire reaction contains several key steps: carbon-carbon bond coupling, proton transfer, hydroxyl departure, indole addition, and deprotonation process. According to the energetic span model, iodine(III)-based donor catalysts exhibit higher catalytic activity than iodine(I)-based catalysts and double cationic catalysts are more potent than single cationic ones. For halogen bond catalysis, the Gibbs energy barriers have linear relation to the electron density at the halogen bond critical points. Furthermore, the Gibbs energy barriers are also linearly related to the integral charge values of the increased region of electron density outside the oxygen atom of reactants. Therefore, the stronger halogen bond results in lower Gibbs energy barrier, and the stronger polarization further benefits the halogen bond catalysis.

DIMERIZATION AND HYDRATION OF GLYOXYLIC ACID: A COMPUTATIONAL STUDY

The hydrogen-bonded dimers and 1:1 complexes formed between glyoxylic acid (GA) and H2O have been investigated employing computational techniques like Natural Bond Orbital (NBO) analysis and Atoms in Molecules (AIM) etc. All calculations are carried at B3LYP/6-311++G** level. Seven dimers and four monohydrates are located on the potential energy surface (PES) each for intramolecular hydrogen bonding (IHB) stabilized G3 and non-IHB stabilized rotamer G1. The most stable dimer and hydrate are formed by non-IHB stabilized rotamer G1. In the most stable dimer, two GA units interact in a duo of C=O…H-O hydrogen bonds forming an eight-membered ring structure. In most stable hydrate, H2O acts as a hydrogen bond acceptor and GA acts as an HB donor. The stabilization energies are calculated and the effect of basis set superposition errors (BSSE) is also considered. A good correlation is found between S.E. and the sum of AIM electron densities at bond critical points for both dimers and hydrates. The gas phase hydration and clustering of GA drive new particle formation for atmospheric aerosols, which affect climate, weather, and human health, hence the study has a significant environmental concern.

Electron Density Analysis of Metal–Metal Bonding in a Ni4 Cluster Featuring Ferromagnetic Exchange

We present a combined experimental and theoretical study of the nature of the proposed metal-metal bonding in the tetranuclear cluster Ni4(NPtBu3)4, which features four nickel(I) centers engaged in strong ferromagnetic coupling. High-resolution single-crystal synchrotron X-ray diffraction data collected at 25 K provide an accurate geometrical structure and a multipole model electron density description. Topological analysis of the electron density in the Ni4N4 core using the quantum theory of atoms in molecules clearly identifies the bonding as an eight-membered ring of type [Ni-N-]4 without direct Ni-Ni bonding, and this result is generally corroborated by an analysis of the energy density distribution. In contrast, the calculated bond delocalization index of ∼0.6 between neighboring Ni atoms is larger than what has been found for other bridged metal-metal bonds and implies direct Ni-Ni bonding. Similar support for the presence of direct Ni-Ni bonding is found in the interacting quantum atom approach, an energy decomposition scheme, which suggests the presence of stabilizing Ni-Ni bonding interactions with an exchange-correlation energy contribution approximately 50% of that of the Ni-N interactions. Altogether, while the direct interactions between neighboring Ni centers are too weak and sterically constrained to bear the signature of a topological bond critical point, other continuous measures clearly indicate significant Ni-Ni bonding. These metal-metal bonding interactions likely mediate direct ferromagnetic exchange, giving rise to the high-spin ground state of the molecule.

Stability of FeVO4-II under Pressure: A First-Principles Study

In this work, we report first-principles calculations to study FeVO4 in the CrVO4-type (phase II) structure under pressure. Total-energy calculations were performed in order to analyze the structural parameters, the electronic, elastic, mechanical, and vibrational properties of FeVO4-II up to 9.6 GPa for the first time. We found a good agreement in the structural parameters with the experimental results available in the literature. The electronic structure analysis was complemented with results obtained from the Laplacian of the charge density at the bond critical points within the Quantum Theory of Atoms in Molecules methodology. Our findings from the elastic, mechanic, and vibrational properties were correlated to determine the elastic and dynamic stability of FeVO4-II under pressure. Calculations suggest that beyond the maximum pressure covered by our study, this phase could undergo a phase transition to a wolframite-type structure, such as in CrVO4 and InVO4.

Revealing self-aggregation mechanism of asphaltenes during oxidative aging using quantum mechanical calculations

The density functional theory (DFT-D3) was used to reveal the molecular mechanisms responsible for self-aggregation of asphaltene. The results showed that electrostatic potential on the molecular vdW surface, atomic charge distribution and transfer, highest occupied, also lowest unoccupied orbitals all appeared at the aromatic rings and heteroatoms that in the aromatic core or aliphatic side chains of asphaltene molecules. The polar functional groups introduced by oxidation changed the electrostatic potential and charge distribution on these regions, which resulted in that electron over carbonyl groups (CO) around the aromatic core decreased the spatial extent of the π-electron cloud and the electron density, thus reduced some favorable contribution of π-π stacking effect in this region. The loss of interactions was partially compensated for by new forms of OH··N hydrogen bond and θ-θ interaction between the side chains in another part of the molecules. Compared to unoxidized dimer, the contribution of electrostatic interaction of oxidized asphaltenes enhanced from 2.42 % to 8.08 % and contribution of dispersion attraction slightly reduced from 63.41 % to 53.98 %. Bond critical points (BCPs) were distributed at aromatic rings and heteroatoms and the number of that were increase. The contributions of atom pair (δGpair (%)) around the strong OH··N bond (0.97 %) in oxidized dimer was significantly raised than that of unoxidized dimer (0.61 %). These changes were consistent with the electronic characteristics of asphaltene molecules after oxidation.

Behavior of HF and (HF)2 inside a fullerene cage: An in silico study using different density functionals

AbstractAn in silico study on the properties of HF and its dimer inside C60 using density functional theory (DFT) based approaches is presented. For this purpose, 10 different DFT functionals following Jacob's Ladder have been chosen. The geometrical parameters such as bond length and bond angle, of the molecules and their dipole moment have been computed. Two types of orientations, namely, L‐shaped and anti‐parallel of (HF)2 inside C60 are considered, the latter with an extremely short hydrogen bond. HF bond lengths are elongated upon encapsulation in comparison to its free state analogue. The calculated value of stabilization energy of HF@C60 is found to be functional dependent, whereas, (HF)2@C60 is thermodynamically unstable for all the functionals. The kinetic stability of (HF)2@C60 is assessed using the atom‐centered density matrix propagation (ADMP) simulation at 300 K temperature. The red shift in HF stretching frequencies is noticed in all cases. Non‐covalent index (NCI) analysis revealed non‐covalent interactions between HF dimer and the C60 cage. Energy decomposition analysis (EDA) showed a high value for the repulsive ΔEpauli which makes the (HF)2@C60 system unstable except for the functional BP86‐D3 of GGA family. Furthermore, the quantum theory of atoms in molecules (QTAIM) analysis is performed and it confirmed the presence of (3, −1) bond critical point along the hydrogen bond region of the L‐shaped (HF)2@C60.

Conceptual density functional theory for temporary anions stabilized by scaled nuclear charges.

The charge stabilization method has often been used before for obtaining energies of temporary anions. Herein, we combine this method for the first time with conceptual density functional theory (DFT) and quantum theory of atoms in molecules by extending it to the study of nuclear Fukui functions, atom-condensed electronic Fukui functions, and bond critical points. This is applied to temporary anions of ethene and chlorinated ethene compounds, which are known to undergo dissociative electron attachment (DEA). It appears that the method is able to detect multiple valence resonance states in the same molecule, namely, a Π and a Σ state. The obtained nuclear and atom-condensed electronic Fukui functions are interpreted as nuclear forces and electron distributions, respectively, and show clear differences between the Π and Σ states. This enables a more profound characterization and understanding of how the DEA process proceeds. The conclusions are in line with findings from earlier publications, proving that the combination of conceptual DFT with the charge stabilization method yields reasonable results at rather low computational cost.

Structural and Spectral Properties of 4-(5-methyl-[1, 2, 4] triazolo [1, 5-a] pyrimidine-7-yloxy) phthalonitrile: Analysis by TD-DFT Method, ADME Analysis, and Molecular Docking Simulations

In this study, 4-(5-methyl-[1,2,4]triazolo[1,5-a]pyrimidine-7-yloxy) phthalonitrile (coded as MTPPN) was chosen as the phthalonitrile compound and the quantum chemical and in-silico studies have been done. First, the basis set of the time dependent density functional theory (TD-DFT) method was used and the boundary orbital energies and band gap calculations of the molecule were performed. Analysis of atoms in molecules (AIM) theoretical calculations is presented to learn about electron density and bond critical point. In addition, absorption, distribution, metabolism, and excretion analyzes (ADME) were performed for the drug potential of the compound. On some enzymes effect of MTPPN compound was examined. The docking score was obtained for AChE, BChE, α-GLY proteins -7.864, -6.848, and -5.511 kcal/mol, respectively. MTPPN gave a good inhibitory performance in an in-silico study as a drug candidate.

Atoms in molecules theory, electrostatic potential surface and frontier molecular orbital analyses on water multimers and pyridine – Water hydrogen bonded complexes

Atoms in molecules theory, electrostatic potential surface and frontier molecular orbital analyses have been carried out on water multimers and their H – bonded complexes with pyridine (Py). The electron density ρr/Laplacian of electron density ∇2ρr values at the bond critical points (BCPs) of the classical/non-classical hydrogen bonds between water and Py exceed/subceed the proposed range of literature values. Based on the literature reports, the criteria for weak and medium H – bonds have been proposed. The ∇2ρr values indicate that the covalent character of the donor O-H bonds decrease/increase upon classical O-H⋯N/ non-classical O-H⋯π H – bonds. The electrostatic potential analysis shows that the nucleophilic nature of oxygen atoms becomes weaker with increase of multimer order. The bonding orbitals of the classical H – bonded Py – water complexes suffer severe change while that of the non-classical H – bonded complexes exactly resembles the Py monomer bonding orbitals.

Testing of Exchange-Correlation Functionals of DFT for a Reliable Description of the Electron Density Distribution in Organic Molecules

Researchers carrying out calculations using the DFT method face the problem of the correct choice of the exchange-correlation functional to describe the quantities they are interested in. This article deals with benchmark calculations aimed at testing various exchange-correlation functionals in terms of a reliable description of the electron density distribution in molecules. For this purpose, 30 functionals representing all rungs of Jacob's Ladder are selected and then the values of some QTAIM-based parameters are compared with their reference equivalents obtained at the CCSD/aug-cc-pVTZ level of theory. The presented results show that the DFT method undoubtedly has the greatest problems with a reliable description of the electron density distribution in multiple strongly polar bonds, such as C=O, and bonds associated with large electron charge delocalization. The performance of the tested functionals turned out to be unsystematic. Nevertheless, in terms of a reliable general description of QTAIM-based parameters, the M11, SVWN, BHHLYP, M06-HF, and, to a slightly lesser extent, also BLYP, B3LYP, and X3LYP functionals turned out to be the worst. It is alarming to find the most popular B3LYP functional in this group. On the other hand, in the case of the electron density at the bond critical point, being the most important QTAIM-based parameter, the M06-HF functional is especially discouraged due to the very poor description of the C=O bond. On the contrary, the VSXC, M06-L, SOGGA11-X, M06-2X, MN12-SX, and, to a slightly lesser extent, also TPSS, TPSSh, and B1B95 perform well in this respect. Particularly noteworthy is the overwhelming performance of double hybrids in terms of reliable values of bond delocalization indices. The results show that there is no clear improvement in the reliability of describing the electron density distribution with climbing Jacob's Ladder, as top-ranked double hybrids are also, in some cases, able to produce poor values compared to CCSD.

Supramolecular Diversity, Theoretical Investigation and Antibacterial Activity of Cu, Co and Cd Complexes Based on the Tridentate N,N,O-Schiff Base Ligand Formed In Situ

The four new complexes, [Cu(HL1)(L2)Cl] (1), [Cu(HL1)(L1)]∙Cl∙2H2O (2), [Co(L1)2]∙Cl (3) and [Cd(HL1)I2]∙dmso (4), have been prepared by one-pot reactions of the respective chloride or iodide metal salt with a non-aqueous solution of the polydentate Schiff base, HL1, resulted from in situ condensation of benzhydrazide and 2-pyridinecarboxaldehyde, while a ligand HL2, in case of 1, has been formed due to the oxidation of 2-pyridinecarboxaldehyde under reaction conditions. The crystallographic analysis revealed that the molecular building units in 1-4 are linked together into complex structures by hydrogen bonding, resulting in 1D, 2D and 3D supramolecular architectures for 1, 2 and 4, respectively, and the supramolecular trimer for 3. The electronic structures of 1-4 were investigated by the DFT theoretical calculations. The non-covalent interactions in the crystal structures of 1-4 were studied by means of the Hirshfeld surface analysis and the QTAIM theory with a special focus on the C-H⋯Cl bonding. From the DFT/DLPNO-CCSD(T) calculations, using a series of charged model {R3C-H}0⋯Cl- assemblies, we propose linear regressions for assessment of the interaction enthalpy (ΔH, kcal mol-1) and the binding energy (BE, kcal mol-1) between {R3C-H}0 and Cl- sites starting from the electron density at the bond critical point (ρ(rBCP), a.u.): ΔH = -678 × ρ(r) + 3 and BE = -726 × ρ(r) + 4. It was also has been found that compounds 1, 3 and 4 during in vitro screening showed an antibacterial activity toward the nine bacteria species, comprising both Gram-positive and Gram-negative, with MIC values ranging from 156.2 to 625 mg/L. The best results have been obtained against Acinetobacter baumannii MβL.

Para-substituted pyridines: Effects on the interaction with 2-perfluoropropyl iodide and vibrations

Vibrational spectroscopy and quantum chemical calculations were employed to investigate the impact of electron donating and electron withdrawing para-substituents on pyridine in terms of molecular and electronic structure, electrostatic properties and the seven in-plane, ring-related vibrational normal modes (RNMs), along with the capability of pyridinyl nitrogen atom to get involved in halogen bonding (XB) with 2-perfluoropropyl iodide (iso-C3F7I). A descriptor was proposed to quantitatively describe pyridine's para-substituents’ electron donating/withdrawing ability. Some quantitative correlations were then identified for the geometric and topological characteristics on bond critical points of XB complexes, the frequency shifts of some RNMs upon XB and thermodynamic quantities of XB formation versus the aforementioned substitution descriptors. Natural bond orbital (NBO) analysis established the formation of XB is beyond a mere electrostatic interaction. Such a XB occurring between the electron lone pair of pyridinyl N and I on iso-C3F7I indicated a strong charge transfer (CT) character. The comparison between the FT-IR/ Raman spectra of 6 binary systems and the calculated spectra for monomers and XB dimer revealed the potential halogen bond between the substituents and iso-C3F7I as well as the intermolecular hydrogen bond (HB) between two same molecules of some substituted pyridines.

Exploring Solid‐State Supramolecular Architectures of Penta(carboxymethyl)diethylenetriamine: Experimental Observation and Theoretical Studies

AbstractCrystals of penta(carboxymethyl)diethylenetriamine have been structurally characterized through single‐crystal X‐ray diffraction analysis. X‐ray diffraction analysis reveals that various non‐covalent interactions combine to determine the crystal packing and final solid‐state supramolecular assembling behavior. The title compound exhibited various 2D supramolecular networks generated through O−H⋅⋅⋅O and C−H⋅⋅⋅O interactions. The C−H⋅⋅⋅O interactions are pivotal in building a two‐dimensional framework, whose formation is readily analyzed with zero‐dimensional centrosymmetric dimeric rings as building blocks within the structure. All the intermolecular interactions are quantified through Hirshfeld surface analysis and fingerprint plots. Energy frameworks are constructed to analyze the dominant interaction energy involved in molecular packing strength. Bader's quantum theory of “atoms‐in‐molecules” (QTAIM) has been used to analyze and characterize non‐covalent interactions. The QTAIM analysis validates the existence of hydrogen bonding contacts, and the topological properties of bond critical points (BCPs), such as the electron density ρ(r) and its Laplacian ∇2ρ(r), are presented to correlate with the interaction energy. The topological analysis revealed that all of the interactions are closed‐shell interactions. Finally, the “Non‐covalent Interaction” (NCI) plot index illustrates the solid‐state supramolecular networks.

TDDFT investigation of solvent polarity related excited state intramolecular proton transfer in 2-(4′-hydroxyphenyl)-3-hydroxybenzo[g]quinolone

In view of potential applications of fluorescent probe for the novel 2-(4′-hydroxyphenyl)-3-hydroxybenzo[g]quinolone (2HP3HBQ) chemosensor, herein, we mainly focus on exploring effect of solvent polarity on ESIPT behavior for 2HP3HBQ. Firstly, we compare infrared (IR) vibrational behaviors and geometric parameters, we check intramolecular hydrogen bond O1-H2⋯O3 could be strengthened in S1 state. Combining bond critical point (BCP) with empirical formula for predicting bond energy, we present nonpolar solvents are more conducive to strengthening hydrogen bonds. Studying frontier molecular orbitals (MOs), we clarify intramolecular charge transfer (ICT) in excited molecule, and charge redistribution facilitates ESIPT. In particular, nonpolar solvent is more propitious to ESIPT. Via keeping two coordinates, we construct potential energy surfaces (PESs) by restrictive optimization. Separating potential energy curves (PECs) along with O1-H2⋯O3, we clarify solvent-polarity-regulated ESIPT mechanism for 2HP3HBQ system. We sincerely wish our work paves the way for designing highly efficient fluorescent probes for 3HBQ derivatives.