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Background: Accurate segmentation of brain glioma is a critical prerequisite for clinical diagnosis, surgical planning and treatment evaluation. In current clinical workflow, physicians typically perform delineation of brain tumor subregions slice‐by‐slice, which is more susceptible to variabilities in raters and also time‐consuming. Besides, even though convolutional neural networks (CNNs) are driving progress, the performance of standard models still have some room for further improvement. Purpose: To deal with these issues, this paper proposes an attention‐guided multi‐scale context aggregation network (AMCA‐Net) for the accurate segmentation of brain glioma in the magnetic resonance imaging (MRI) images with multi‐modalities. Methods: AMCA‐Net extracts the multi‐scale features from the MRI images and fuses the extracted discriminative features via a self‐attention mechanism for brain glioma segmentation. The extraction is performed via a series of down‐sampling, convolution layers, and the global context information guidance (GCIG) modules are developed to fuse the features extracted for contextual features. At the end of the down‐sampling, a multi‐scale fusion (MSF) module is designed to exploit and combine all the extracted multi‐scale features. Each of the GCIG and MSF modules contain a channel attention (CA) module that can adaptively calibrate feature responses and emphasize the most relevant features. Finally, multiple predictions with different resolutions are fused through different weightings given by a multi‐resolution adaptation (MRA) module instead of the use of averaging or max‐pooling to improve the final segmentation results. Results: Datasets used in this paper are publicly accessible, that is, the Multimodal Brain Tumor Segmentation Challenges 2018 (BraTS2018) and 2019 (BraTS2019). BraTS2018 contains 285 patient cases and BraTS2019 contains 335 cases. Simulations show that the AMCA‐Net has better or comparable performance against that of the other state‐of‐the‐art models. In terms of the Dice score and Hausdorff 95 for the BraTS2018 dataset, 90.4% and 10.2 mm for the whole tumor region (WT), 83.9% and 7.4 mm for the tumor core region (TC), 80.2% and 4.3 mm for the enhancing tumor region (ET), whereas the Dice score and Hausdorff 95 for the BraTS2019 dataset, 91.0% and 10.7 mm for the WT, 84.2% and 8.4 mm for the TC, 80.1% and 4.8 mm for the ET. Conclusions: The proposed AMCA‐Net performs comparably well in comparison to several state‐of‐the‐art neural net models in identifying the areas involving the peritumoral edema, enhancing tumor, and necrotic and non‐enhancing tumor core of brain glioma, which has great potential for clinical practice. In future research, we will further explore the feasibility of applying AMCA‐Net to other similar segmentation tasks. [ABSTRACT FROM AUTHOR]

Investigating the effects of surrounding microenvironments and substituents on the excited‐state proton transfer (ESPT) mechanism have always been a great challenge, especially in protic solvents and solid state. In this work, a detailed theoretical study on ESPT processes of salicylic acid (SA) and its two derivatives (5ASA and 5NSA) in gas, cyclohexane, acetonitrile, ethanol (EtOH), and crystal phases is performed based on the density functional theory (DFT) and time‐dependent DFT as well as the combined quantum mechanics/molecular mechanics (QM/MM) methods. Intramolecular charge transfer‐induced aggregation‐caused quenching phenomenon of 5ASA is unveiled utilizing the hole–electron analysis. Independent gradient model analysis is implemented to reveal the spontaneous forward proton transfer (PT) behavior of 5ASA. Besides, potential energy surfaces are constructed to evaluate the dominant PT pathway in EtOH, and the related transition state structures are also obtained to accurately provide the intra‐ and inter‐PT energy barriers. Eventually, excited‐state ab initio molecular dynamics computation reaffirms that the intra‐PT reaction is predominant for SA. This theoretical work comprehensively explores the ESPT mechanism and luminescent properties of SA and its two derivatives, which provides a reference for developing efficient organic light‐emitting materials based on ESPT chromophores. [ABSTRACT FROM AUTHOR]

A fluorescent probe 2′-(2,4-dinitro-phenoxy)-4-(dimethylamino) chalcone (Pr1, Spectrochim. Acta, Part A 2021, 244, 118839) based on twisted intramolecular charge transfer (TICT) and excited state intramolecular proton transfer (ESIPT) was designed and synthesized recently for the detection of H2S and biothiols in aqueous solutions and cells. Along with the single fluorescence phenomenon in the experiment, it is worth analyzing whether the ESIPT process emerges, and the detailed sensing mechanism of Pr1 as a fluorescence probe needs to be explored in depth. Herein, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods were exploited to investigate the geometric structures and fluorescence properties for Pr1 and its product 2′-hydroxy-4-(dimethylamino) chalcone (Comp2) after adding H2S/biothiols. The geometrical structure parameters, reduced density gradient (RDG) analysis and infrared vibrations associated with the hydrogen bond for Comp2 indicate that the intramolecular hydrogen bond is strengthened upon photo-excitation compared with the S0 state, and the existence of the ESIPT process was confirmed by the potential energy curve. In addition, the results of hole–electron analysis and frontier molecular orbitals explained the inducement of fluorescence quenching for Pr1 and the mechanism of fluorescence emission for Comp2. In consequence, the phenomenon of a single fluorescence peak for the ESIPT-based active dye Comp2 in experiments is expounded by the Boltzmann distribution, which provides a theoretical reference for the development of novel fluorescent probes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of novel dyes for DSSCs were designed via introducing different π-bridges. • The photophysical parameters of the studied dyes are calculated by DFT/TD-DFT methods. • Intramolecular charge transfer can be promoted by improving the coplanarity of dyes. • Introduction of BTH π-bridge contributes to the decrease of recombination energy. • B dye exhibits the prominent absorption red-shift and photoelectrical properties. In the synthesis experiment (Dyes Pigm., 2020, 174, 108026), it was found that the 10 and 11 dyes have the excellent red-shift value in the absorption spectrum, so we replaced the conjugated bridges of 10 and 11 by introducing different functional groups, four novel dyes (A, B, C, D) are designed as the photoactive layers of dye-sensitized solar cells (DSSCs). Compare with other dyes, it is worth noting that the designed dye B displays the narrowest energy gap, the most obvious red shift of absorption peak (∼545 nm), the best charge separation ability and the most outstanding electron transport performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of –CN/–NH 2 substitutions at different positions on the ESIPT of HPP1 were investigated. • ESIPT barrier can be regulated by the type and position of the substituents. • Amino substituted derivatives have a fluorescence off–on mechanism for the detection of hydrazine. • Cyano-substituted derivatives have larger Stokes-shift than HPP1. In the present work, four probe molecules for detecting hydrazine have been designed based on the 2-(4-Acetoxy-3-benzothiazole-2-yl-phenyl)-4-methyl-thiazole- 5-carboxylic acid ethyl ester (HP1) to investigate the influence of the amino and cyano groups on the excited-state intramolecular proton transfer (ESIPT) behavior and photophysical properties. The changes in hydrogen bond strength indicate that the intramolecular hydrogen bond of all probe products is enhanced upon photoexcitation. Frontier molecular orbitals (FMOs) and natural bond orbital (NBO) reveal the driving force of ESIPT. In addition, the potential energy curves and transition state theory explain the reason for the single fluorescence phenomenon in the experiment. The simulated absorption and fluorescence spectra of HP1 and its product (HPP1) are completely consistent with the experimental results, which also verify the viewpoint. Meanwhile the cyano derivative HPP4 exhibits a larger Stokes-shift (201 nm) than that of HPP1 (145 nm) and has the same low energy barrier as HPP1. These excellent properties allow HPP4 to be a fluorescent probe with superior performance than the original molecule. In conclusion, this work can provide a theoretical basis for the design and synthesis of more sensitive fluorescent probes for the detection of hydrazine. [ABSTRACT FROM AUTHOR]

[Display omitted] • ESIPT properties of nine molecules are studied by DFT and TD-DFT methods. • The substitution of weak electronegative atoms can facilitate ESIPT reaction. • The substitution on oxazole ring has more conspicuous effect on ESIPT process and photophysical properties. • Both S and Se substituted derivatives are fluorescence quenched. 2-(2-carbomethoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole (DCl-O) has been extensively studied due to its excited-state intramolecular proton transfer (ESIPT) characteristics. To obtain molecules with better luminescence properties, eight derivatives were designed by using different atomic (S, Se and F, Cl) substitution for further study the influence of electronegativity on ESIPT properties. The ESIPT process and photophysical characters of DCl-O and derivatives were studied with theoretical methods. The analysis indicates that hydrogen bonds were strengthened upon photo-excitation. Moreover, the ESIPT reaction is more facile to proceed in derivatives with the weak electronegativity of substitution and the substitution of chalcogen has better effect than that of halogen. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ESIDPT reaction for BJu is stepwise rather than concerted. • ICT process causes the fluorescence quenching phenomenon of Ju. • Dimerization enhances the antioxidant activity of Ju in the excited state. • ESDPT process has improved the antioxidant activity of BJu effectively. In this work, the excited-state intramolecular proton transfer (ESIPT) mechanism and antioxidant activity of Juglone (Ju) and its dimer 3,3′-bijuglone (BJu) were systematically compared and analyzed by using the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Via comparing the primary hydrogen bond parameters, reduced density gradient (RDG) versus sign(λ 2)ρ(r) scatter plots, interaction region indicator (IRI) isosurface, topology descriptors, and infrared (IR) spectra, it can be confirmed that all the intramolecular hydrogen bonds (IHBs) of Ju and its dimer 3,3′-bijuglone (BJu) have been enhanced in the lowest excited state (S L). The intramolecular charge transfer (ICT) triggered the fluorescence quenching mechanism for Ju was confirmed based on the hole-electron analysis. Moreover, the calculated S 0 - and S L -stated potential energy surfaces (PESs) have proven that the excited-state intramolecular double proton transfer (ESIDPT) of BJu is stepwise rather than concerted and based on which the detailed proton-transfer (PT) process has been clarified. Compared with the first step PT behavior of BJu, the ESIPT process of Ju has barely been influenced by dimerization. Besides, the computed ionization potential (IP) has substantiated that BJu shown the better antioxidant capacity via the single electron transfer (SET) mechanism than the corresponding monomer Ju in the S L state. The relationship between the PT process and antioxidant activity of Ju and BJu has also been successfully established, which is conducive to design and synthesize highly effective PT-based antioxidants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Attenuating of atomic electronegative facilitates the ESIPT reaction. • Six-membered IHB is the dominant ESIPT channel for the studied compounds. • URA-S and URA-Se own the more significant Stokes shift compared with URA. • ICT process causes the fluorescence weakening phenomenon of K6 forms. In this work, the effects of atomic electronegativity (O, S, and Se atoms) on the competitive double excited-state intramolecular proton transfer (ESIPT) reactions and photophysical characteristics of uralenol (URA) were systematically explored by using the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The calculated hydrogen bond parameters, infrared (IR) vibrational spectra, reduced density gradient (RDG) scatter plots, interaction region indicator (IRI) isosurface and topology parameters have confirmed the six-membered intramolecular hydrogen bond (IHB) O4 H5...O3 is the stronger one in all the three studied compounds. Subsequently, frontier molecular orbitals (FMOs) and natural bond orbital (NBO) population analysis essentially uncover that the electron redistribution has induced the ESIPT process. Besides, the constructed potential energy curves (PECs) have indicated that the ESIPT process prefers to occur along the O4 H5...O3 rather than the O1 H2...O3 and the proton-transfer energy barrier is gradually decreased with the weakening of atomic electronegativity from URA to URA-S and URA-Se. In a conclusion, the attenuating of atomic electronegativity has enhanced the IHBs of URA and thereby promoting the ESIPT reaction, which is helpful for further developing novel fluorophores based on ESIPT behavior in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intramolecular hydrogen bond is weakened as the solvent polarity increased. • Intramolecular charge transfer has triggered ESIPT reaction of 3HF-OH. • ESIPT process of 3HF-OH is inclined to proceed in the weak-polar solvent. • Molecular configuration torsion of 3HF-OH inhibits the ESIPT behavior. In this contribution, the solvent effects on the excited-state intramolecular proton transfer (ESIPT) and photophysical properties of 2-(4-(diphenylamine)phenyl)-3-hydroxy-4H-chromen-4-one (3HF-OH, Dyes Pigm. 2021, 184, 108865) in the dimethylsulfoxide (DMSO), acetonitrile (ACN), dichloromethane (DCM) and cyclohexane (CYH) phases have been comprehensively explored by using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The obtained bond lengths, bond angles and infrared (IR) vibration analysis related to the intramolecular hydrogen bond (IHB) reveal that the IHB intensity of 3HF-OH is weakened as the solvent polarity increased. Besides, the ESIPT process changes from the endothermic to the exothermic with the enlargement of solvent polarity, and the reaction barrier increases gradually. It is worth noting that the molecular configuration torsion of 3HF-OH is gradually intensified with the decline of solvent polarity, which aggravates the twisted intramolecular charge transfer (TICT) state and thereby partially attenuates the short-wavelength fluorescence of 3HF-OH in the CYH solvent. In addition to these, the structural torsion has restrained the occurrence of the ESIPT behavior by means of elevating the energy barrier. This theoretical research would provide valuable guidance for regulating and controlling the photophysical behavior of compounds via the strategy of changing solvent polarity. [ABSTRACT FROM AUTHOR]

• Tuning the ESIPT and photophysical properties by introducing -OCH3 and -CN to SCLPY. • Intramolecular charge transfer has triggered the ESIPT reaction of compounds. • Substitution of methoxyl group can inhibit ESIPT behavior of SCLPY more. • Introduction of cyano group resulted in decrease of fluorescence intensity for enol form. Two novel molecules (SCLPY-MeO and SCLPY-CN) are designed based on the N-salycilidene-5-chloroaminopyridine (SCLPY) via introducing the methoxyl (–OCH 3) and cyano (-CN) groups at the meta-position of the chlorine atom, respectively, to explore the effect of the substitution of electron-withdrawing and donating groups on the excited-state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of SCLPY, employing the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The significant calculated structural parameters associated with the intramolecular hydrogen bonds (IHBs) have demonstrated that the IHBs intensity is enhanced in the excited state and SCLPY is endowed with the strongest IHB. The partial quenching of the short-wavelength fluorescence in SCLPY-CN has been satisfactorily explained by calculating the transition electric dipole moment and the long-wavelength fluorescence of that exhibits the largest Stokes shifts relative to the other molecules. Moreover, introducing the –OCH 3 group has evidently enhanced the luminescent intensity of SCLPY. On account of the potential energy curves (PECs), scanning with gradually elongating the O1-H2 bond, it can be known that the forward proton transfer process is more readily to occur in the S 1 state due to the relatively lower energy barriers compared with the ground state. Moreover, SCLPY is provided with the lowest energy barrier, implying that the ESIPT behavior is most likely inclined to proceed in SCLPY. Therefore, it is well illustrated that the introductions of –OCH 3 and –CN groups indeed have an impact on the ESIPT process and photophysical properties of SCLPY. [Display omitted]. [ABSTRACT FROM AUTHOR]

Recently, a new fluorescent probe AE-Phoswas reported to detect the activity of alkaline phosphatases (ALP) in different living cell lines. Here, we present an in-depth computational analysis of the mechanism and source of the fluorescence of the AE-Phos probe. There is an intermediate product (AE-OH-Phos) in the experiment as well as a different configuration of products that may emit fluorescence. It is essential to investigate the origin of fluorescence and the detection mechanism of the probe, which could help us eliminate the interference of other substances (including an intermediate product and possible isomers) on fluorescence during the experiment. According to the change of geometric parameters and Infrared spectra, we deduce that the dual intramolecular hydrogen bonds of salicylaldehyde azine (SA) were enhanced at the excited state, while AE-OH-Phos was attenuated. Considering the complex ESIPT behavior of the dual proton-type probe, the potential energy surfaces were further discussed. It can be concluded that the single proton transfer structure of SA (SA-SPT) is the most stable form. Both the concerted double proton transfer process and stepwise single proton transfer process of SA were forbidden. The fluorescence for SA was 438 nm, while that of SA-SPT was 521 nm, which agrees with the experimentally measured fluorescence wavelength (536 nm). The conclusion that single proton transfer occurs in SA is once again verified. In addition, the distribution of electron-hole and relative index was analyzed to investigate the intrinsic mechanism for the fluorescence quenching of the probe and the intermediate product. The identification of the origin of fluorescence sheds light on the design and use of dual-proton type fluorescent probes in the future. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach is presented to synthesize microwave medium of negative refractive index by incorporating metallic wire array with negative effective permittivity into the host media such as ferrimagnet-YIG (yttrium iron garnet) applied by external magnetic field whose permeability is negative. We have designed the composite medium having negative refractive index in C/X band frequencies, analyzed and simulated its electromagnetic (EM) properties by use of EM EDA package based on time-domain finite integration method. The simulation results show that: ① the effective permittivity of the designed metallic wire array is negative in the frequency range from 7.02 GHz to 9.80 GHz; ② the permeability of YIG substrate immersed into an external magnetic field is negative in the frequency range from 5.22 GHz to 8.14 GHz; ③ EM wave can pass through the composite medium synthesized by the above designed metallic wire array and YIG substrate, and ④ the negative refraction behavior occurs on the interface between the composite medium and the normal material with positive refractive index in 7.51–8.13 GHz frequency range, in which the effective permittivity of the metallic wire array and the permeability of YIG substrate are negative simultaneously. The full wave simulation has demonstrated that the effective refractive index of the designed composite medium is indeed negative and ascertained that the proposed approach to design microwave medium with negative refractive index is viable. [ABSTRACT FROM AUTHOR]

Although the excited state intramolecular proton transfer (ESIPT) process and photophysical properties of 2-(2-Hydroxy-phenyl)-4(3H)-quinazolinone (HPQ) have been extensively explored, a comprehensive study of the substitution effects on HPQ is still lacking in theory. Given this situation, HPQ molecules with different electronic substituents are systematically investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods in this work. Two different substituents, including –NH 2 (electron-donating group) and –CN (electron-withdrawing group), are selected to complete this study. The fluorescence quenching phenomenon of HPQ in the keto form is well explicated by the twisted intramolecular charge transfer (TICT). Besides, the substitutions of –NH 2 and –CN on HPQ give rise to the larger Stokes shifts and reproduces the dual fluorescence property. The primary parameters related to the intramolecular hydrogen bonds (IHBs) and the infrared (IR) vibration spectra of the O1–H2 reveal that all the IHBs for HPQ and its derivatives are enhanced in the S 1 state. Meanwhile, from the calculated potential energy curves, it can be inferred that the introduction of –NH 2 and –CN enlarges the excited-state energy barrier of the proton transfer process for HPQ. Therefore, we have reason to conclude that the substitutions of –NH 2 and –CN groups on HPQ significantly affect the ESIPT process and triggers distinct photophysical behaviors. [Display omitted] • ESIPT properties of HPQ-based derivatives are studied by DFT and TD-DFT methods. • TICT causes fluorescence quenching of HPQ at keto form. • Dual fluorescence property of HPQ is reappeared by introducing –NH 2 or –CN. • HPQ possesses the lowest excited-state energy barrier among molecules studied. [ABSTRACT FROM AUTHOR]

To design novel materials suitable for high-temperature electromechanical applications, a bismuth-based ternary solid solution system, (1- x - y)BiScO 3 - y Pb(Sc 1/2 Nb 1/2)O 3 - x PbTiO 3 , with compositions situated around the morphotropic phase boundary, were designed and synthesized in the form of ceramic. The crystal structure, microstructure, dielectric, ferroelectric and piezoelectric properties, and the local polar domain structure of the ceramics were investigated in detail. The examined ceramics exhibit large grain sizes ranging from 20 μm to 45 μm, along with noteworthy characteristics, including a relatively large strain of 0.21 %, a high large-signal piezoelectric coefficient (d 33 * = 368 pm/V), a low dielectric loss (tanδ = 1.7 %), and a high Curie temperature (T C ∼ 423 °C). These enhanced properties signify the suitability of the designed ternary ceramics for future high-temperature electromechanical applications. This work demonstrates an effective approach for designing ferro-/piezoelectric materials characterized by substantial strain and low dielectric loss. [ABSTRACT FROM AUTHOR]

To reveal the influence of different substituents on the excited-state intramolecular proton transfer (ESIPT) process and photophysical properties of 4′-N, N-dimethylamino-3-hydroxyflavone (DMA3HF), two novel molecules (DMA3HF-CN and DMA3HF-NH2) were designed by introducing the classical electron-withdrawing group cyano (-CN) and electron-donating group amino (-NH2). The three molecules in the acetonitrile phase were systematically researched by applying the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The excited-state hydrogen bond enhancement mechanism was confirmed, and the hydrogen bond intensity followed the decreasing order of DMA3HF-NH2 > DMA3HF > DMA3HF-CN, which can be explained at the electronic level by natural bond orbital, fuzzy bond order, and frontier molecular orbital analyses. Moreover, we found from the electronic spectra that the fluorescence intensity of the three molecules in keto form is relatively strong. Moreover, the calculated absorption properties indicated that introducing the electron-withdrawing group -CN could significantly improve the absorption of DMA3HF in the ultraviolet band. In summary, the introduction of an electron-donating group -NH2 can promote the ESIPT reaction of DMA3HF, without changing the photophysical properties, while introducing the electron-withdrawing group -CN can greatly improve the absorption of DMA3HF in the ultraviolet band, but hinders the occurrence of the ESIPT reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photophysical properties of the three chalcones were evaluated by QM/MM method. • Absorption spectra of EDDP, EDPO, and EDHP covered the whole UV region. • Geometric structure twisting in glycerol solvent weaken their fluorescence strength. • After-sun repair abilities of the three molecules improved upon photoexcitation. • Three chalcones both possess full-band UV protection and after-sun repair abilities. The photoprotection mechanisms of three chalcones (EDDP, EDPO, and EDHP) in the gas phase and glycerol solvent were investigated using density functional theory and quantum mechanics/molecular mechanics methods. The optimized structures confirmed that the intramolecular hydrogen bonds of the three molecules were enhanced in the S 1 state, which favored their proton transfer process. According to the scanned potential energy curves in the S 1 state, the three molecules can spontaneously undergo proton transfer in the gas phase, and stable keto configurations do not exist in the glycerol solvent due to their unbridgeable energy barriers. Moreover, the absorption spectra of the three molecules covered the entire ultraviolet region, and their fluorescence spectra spread over the visible and infrared regions. Notably, the oscillator strengths of the maximum absorption peaks were far higher than those of the fluorescence peaks, which meets the requirements of sunscreens for molecular photophysical properties. Furthermore, the geometric structure twisting of the three molecules in glycerol solvent consumed part of the energy from ultraviolet light, causing their fluorescence peak strengths to be faint. The interaction force between glycerol solvent and the three molecules was augmented in the S 1 state, explaining why their geometric structure twisted in glycerol solvent. In addition, the three molecules passed our toxicity test, and their free radical scavenging activities were upgraded upon photoexcitation. This property is favorable for promoting their after-sun repair abilities. This work will be expected to deepen the understanding of the sunscreen mechanisms of chalcones. [ABSTRACT FROM AUTHOR]

[Display omitted] • Substituent effect can effectively adjust the photophysical properties of molecules. • Absorption spectra of the studied molecules cover the UVA and UVB region. • BPNS is the most potential to be used as UV absorbers among the studied molecules. In this present work, four novel molecules (BPN, BPNS, BPS, and BPSN), possessing excited-state intramolecular proton transfer (ESIPT) characteristics, were designed to quantify the impacts of substituent effects on their photophysical properties. By exploring the primary geometrical parameters concerning hydrogen bonds, it should be noticed that the intramolecular hydrogen bonds (IHBs) of the studied molecules have been strengthened at S 1 state. Infrared vibrational spectra analysis illustrates that adding electron-donating group thiophene to the proton donor side can weaken the IHBs in comparison to the electron-withdrawing group pyridine. Through investigating the absorption and fluorescence spectra, it can be clearly found that the maximum absorption peaks of the studied molecules are all located in the UVA region, and their regions of fluorescence peaks are harmless to human skin. Furthermore, considering the light intensity factor, it can be concluded that BPNS is the most potential to be used as UV absorbers in the studied molecules. This work investigates the effects of the positions and types of substituent groups on photophysical properties of 2-(2′-hydroxyphenyl) benzazoles derivatives, which can help design and exploit novel UV absorbers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Introducing different substituents has inhibited the ESIPT reaction of DHAQ. • Strength relationship of dual IHBs could be switched by substituent effect. • Dominant ESIPT channel is irrelevant to the types of substituents introduced. • DHAQ-COOH and DHAQ-CN own a larger Stokes shift compared with DHAQ. In this work, to unveil the substituent effect on the excited-state intramolecular proton transfer (ESIPT) reaction of 1,8-Dihydroxyanthraquinone (DHAQ), four derivatives DHAQ-Me, DHAQ-NH 2 , DHAQ-COOH, and DHAQ-CN were considered using quantum chemistry methods in the acetonitrile (ACN) phase. The excited-state intramolecular hydrogen bonds (IHBs) (O1-H2⋯O3 and O5-H4⋯O3) strengthening mechanism was confirmed by computing primary geometric parameters, infrared (IR) spectra and reduced density gradient (RDG) scatter plots. The strength relationship of the dual IHBs within all the investigated compounds was established based on the calculated binding energies. Charge-recombination triggered ESIPT mechanism has been demonstrated by the analysis of frontier molecular orbitals (FMOs) and natural bond orbital (NBO) population. Besides, the hole-electron analysis indicates that a remarkable intramolecular charge transfer (ICT) behavior has induced the fluorescence intensity to decrease significantly for DHAQ-NH 2 in K1 form. DHAQ derivatives with electron-withdrawing groups substituted (DHAQ-COOH and DHAQ-CN) have exhibited a larger Stokes shift, which is a desirable property for manufacturing luminescent materials. From the located transition state (TS) structures and the calculated potential energy curves (PECs), it is noticeable that the dominant channel for ESIPT reactions is always the O1-H2⋯O3 hydrogen bonding wire, which is irrelevant to the types of substituents introduced, although O5-H4⋯O3 is the stronger one for DHAQ-Me and DHAQ-NH 2. This theoretical research may well deepen the comprehension of the relationship between IHB and ESIPT behavior and thereby provide valuable guidance to synthesize efficacious ESIPT-based organic chromophores experimentally. [ABSTRACT FROM AUTHOR]