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Nanoparticle motion and self-assembly have been regarded as a promising pathway for forming ordered nanostructures. However, the detailed dynamics processes induced by ligand involvement remained poorly understood. Here, we used in situ liquid-cell electron microscopy technology to image the formation of face-to-face Pt cube ordered structures: pairs, linear chains, and squares. The van der Waals interaction between the two neighboring cubes was quantified in real time. Interestingly, the two different formation processes of the square phase were achieved via a rotational and translational method. It is found that the space between two neighboring cubes was the same as the ex-TEM results. The density functional theory calculation demonstrated that it was attributed to the DMF ligand interactions of the cubes that promoted their face-to-face attachment.

At present, albeit the dexterous hand prostheses of multiple degrees of freedom (DOFs) have become prosperous on the market, the user’s demand on intuitively operating these devices have not been well addressed so that their acceptance rate is relatively low. The unintuitive control method and inadequate sensory feedback are frequently cited as the two barriers to the successful application of these dexterous products. Recently, driven by the wave of artificial intelligence (AI), a series of shared control methods have emerged, in which “bodily function” (myoelectric control) and “artificial intelligence” (local autonomy, computer vision, etc.) are tightly integrated, and provided a new conceptual solution for the intuitive operation of dexterous prostheses. In this paper, the background and development trends of this type of methods are described in detail, and the potential development directions and the key technologies that need breakthroughs are indicated. In practice, we instantiate this shared control strategy by proposing a new method combining simultaneous myoelectric control, multi-finger grasp autonomy, and augmented reality (AR) feedback together. This method “divides” the human sophisticated reach-and-grasp task into several subtasks, and then “conquers” them by using different strategies from either human or machine perspective. It is highly expected that the shared control methods with hybrid human-machine intelligence could address the control problem of dexterous prostheses.

In this work, DFT and TDDFT approaches have been executed to make a detailed exploration about the excited state luminescent properties as well as excited state intramolecular proton transfer (ESIPT) mechanism for the novel 2-(1H-imidazol-2-yl)-phenol (PI) compound. Optimized geometrical parameters of primary chemical bonds and infrared (IR) spectra prove that the O37-H38···N26 hydrogen bond of PI should be strengthened in the S1 state. Insights into frontier molecular orbitals (MOs), we infer charge redistribution and charge transfer (ICT) phenomena motivate ESIPT trend. Via probing into potential energy curves (PECs) in related electronic states, we come up with the ultrafast ESIPT behavior due to low potential barrier. Furthermore, we search the reaction transition state (TS) and simulate intrinsic reaction coordinate (IRC) path; the ultrafast ESIPT behavior and mechanism of PI compound can be re-confirmed. We sincerely wish that this work could play roles in further developing novel applications based on PI compound and in promoting new ratiometric fluorescence probes in the future.

Intrinsic flexible structures enable a continuum manipulator to exhibit attractive dexterity and intrinsic compliance over traditional hyper-redundant robots. However, its insufficient stiffness makes the performance of continuum manipulators unsatisfactory and thus limits the applications in many fields. A significant challenge is how to make a trade-off among dexterity, compliance and stiffness. From an evolutionary perspective, this paper compares several biological structures that enable the continuum manipulator function, and intends to reveal the mechanism on how the biological structures can improve the stiffness. The notochord and the vertebral column with acoelous centra are abstracted and physically implemented. A fundamental rod-driven continuum manipulator is also introduced as a comparison. The stiffness models of these three continuum manipulators are proposed, and comparative experiments are conducted to verify their stiffness properties. Our results demonstrate that the rigid-flexible segmental structure can improve the stiffness properties of a continuum manipulator.

In this work, N,N’-bis(salicylidene)-(2-(3′,4′-diaminophenyl)benzothiazole) (named as “BTS”) system was studied about its excited-state intramolecular proton transfer (ESIPT) process. The analyses about reduced density gradient (RDG) reveal the formation of two intramolecular hydrogen bonds in BTS system. Bond lengths and angles, infrared (IR) vibrations as well as frontier molecular orbitals (MOs) using TDDFT method indicate that the strength of hydrogen bond should be enhanced in the S1 state. Particularly, hydrogen bond O1–H2···N3 undergoes larger variations compared with O4–H5···N6, which infers that hydrogen bond O1–H2···N3 may play a decisive role in the ESIPT process of BTS system. Given the two hydrogen bonds of BTS molecule, two types of potential energy curves have been constructed, which confirms that only single proton transfer process occurs due to lower energy barrier along with O1–H2···N3 rather than O4–H5···N6. This work not only presents a reasonable explanation for previous experiment, but also clarifies the specific ESIPT mechanism for BTS system.

Using TDDFT method, modulating mechanism of N H-based excited-state intramolecular proton transfer by electron-withdrawing substituent cyano at the aromatic para-position of four 2-(2′-aminophenyl) benzothiazole compounds have been demonstrated at B3LYP/6-311+G(d, p)/IEFPCM theory level. The scanned potential energy curves reveal that introduction of a strong electron-withdrawing group tosyl at the amino nitrogen can remarkably facilitate the occurrence of the ESIPT reaction, whereas introduction of a weak electron-withdrawing group acetyl at the amino nitrogen or introduction of an electron-withdrawing cyano group on the benzene ring at the para-position with respect to the amino group can contribute to the ESIPT process in certain degree.

We perform a theoretical investigation about the excited state intramolecular proton transfer (ESIPT) reaction for a novel 2-(2-hydroxy-3,5-dimethyl-phenyl)-benzooxazole-5-carboxylicacid (HDPBC) system. The ultrafast excited state process is due to the low potential barrier, which should be the reason why only one fluorescence peak can be observed in previous experiment. Comparing the potential energy barriers in different aprotic solvents, we present nonpolar solvents play roles in facilitating ESIPT process for HDPBC molecule. This work not only clarifies the detailed ESIPT mechanism for the novel HDPBC system and explains experimental phenomenon, but also present that solvent effects could control the ESIPT process.

We design novel graphyne/blue phosphorene van der Waals (vdW) heterostructures (G/BP) under the external electric fields (Efield) and strains. It is demonstrated that the G/BP is a type-I semiconductor with a direct band gap of approximately 0.378 eV. The external Efield and strains not only have important effects on the band structure which undergoes a fascinating direct-indirect and semiconductor-metal transitions, but also influence the band alignment which experiences transition from type-I to type-II. In brief, the features of tunable bandgap and controllable band alignment endow G/BP with potential for application in future optoelectronic devices.

The N H-based excited-state intramolecular proton transfer process of 2-(2′-aminophenyl)benzothiazole (PBT-NH2) and its three derivatives have been explored by the time-dependent density functional theory (TD-DFT) method. The scanned potential energy curves reveal that the energy barriers of the first singlet excited state of the four compounds along the ESIPT reactions are predicted at 8.74, 8.98, 6.72 and 1.69 kcal/mol respectively, suggesting that the inclusion of a strong electron-withdrawing tosyl (Ts) group can remarkably facilitate the occurrence of the ESIPT reaction, while the involvement of an electron-donating methyl group has slight opposite effect on the ESIPT process of the amino-type hydrogen-bonding system.

A novel fluorescence molecule (2‑hydroxy‑4‑methoxyphenyl)(phenyl)‑methanone azine (HMPM) has been explored theoretically in this present work. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we investigate the excited state hydrogen bonding behaviors and excite state intramolecular proton transfer (ESIPT) process for HMPM molecule. Via simulating the reduced density gradient (RDG) versus sign(λ2)ρ, we firstly verify the double intramolecular hydrogen bonds (O1H2⋯N3 and O4H5⋯N6) for HMPM system. Comparing with the changes about these two hydrogen bonds (i.e., bond distances, bond angles and infrared (IR) vibrational spectra), we find that they should be enhanced in the first excited state upon the photo-excitation. The shortened hydrogen bonding distance of H2⋯N3 and H5⋯N6 provide the possibility for ESIPT reaction. Given the photo-excitation process, we confirm the charge redistribution around the hydrogen bonding moieties plays an important role as a driving force for the ESIPT process. Further, via constructing S0-state and S1-state potential energy surfaces (PESs), we confirm the excited state double proton transfer (ESDPT) is excludable since the high optimized energy and high potential energy barrier. While the low potential barrier for excited state single proton transfer path results in the ultrafast ESIPT reaction, which explains why the initial HMPM fluorescence peak cannot be detected in previous experimental phenomenon. This work not only clarifies the excited state dynamical behavior for HMPM system, but also explains previous experimental phenomenon and attributions about steady state spectra. We hope this work can facilitate novel applications based on the novel HMPM system in future.

Plant electrophysiology lays the foundation for smart plant interrogation and intervention. However, plant trichomes with hair-like morphologies present topographical features that challenge stable and high-fidelity non-invasive electrophysiology, due to the inadequate dynamic shape adaptability of conventional electrodes. Here, this issue is overcome using a morphable ionic electrode based on a thermogel, which gradually transforms from a viscous liquid to a viscoelastic gel. This transformation enables the morphable electrode to lock into the abrupt hairy surface irregularities and establish a conformal and adhesive interface. It achieves down to one tenth of the impedance and 4-5 times the adhesive strengths of conventional hydrogel electrodes on hairy leaves. As a result of the improved electrical and mechanical robustness, the morphable electrode can record more than one order of magnitude higher signal-to-noise ratio on hairy plants and maintains high-fidelity recording despite plant movements, achieving superior performance to conventional hydrogel electrodes. The reported morphable electrode is a promising tool for hairy plant electrophysiology and may be applied to diversely textured plants for advanced sensing and modulation. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) The authors thank the financial support from the Agency for Science, Technology and Research under its AME Programmatic Funding Scheme (A18A1b0045), the National Research Foundation, Prime Minister’s Office, Singapore, under its NRF Investigatorship (NRFNRFI2017- 07), and Singapore Ministry of Education (MOE2019-T2-2-022).

Excited state intramolecular proton transfer (ESIPT) of organic molecules has been drawing continuously considerable interests. This reaction is not only one of the most basic processes in life, but also exists in wide of application fields. In this work, we theoretically make a thorough inquiry about molecular excited state trends and ESIPT procedures for the novel highly miscible 2-benzothiazole-2-yl-5-hex-1-ynyl-phenol (BYHYP) molecule. Based on DFT and TDDFT means, we firstly examine and certify hydrogen bond O–H···N role in BYHYP. Probing into molecular structure, infrared (IR) vibrational behaviors and computational hydrogen bonding energies, we validate O–H···N of BYHYP is enhanced in S1-state via photoinduced excitation. Accessorial negative electronic densities over N atom facilitate attracting hydrogen proton, which caters to the truth of strengthening hydrogen bond in S1. In addition, frontier orbital gap indicates that the solvent polarity plays vital roles in affecting excited state courses for BYHYP system. By means of potential energy curves (PECs) in four kinds of solvents, we propose the ultrafast ESIPT mechanism for BYHYP by explaining previous experimental characteristics. Along the way of ESIPT, we search the transition state (TS) and present the regulation mechanism for BYHYP via solvent effects.

Theoretical studies of the potential energy surfaces (PESs) and bound state calculations were performed for Ar–AgX (X = F, Cl, Br, and I) complexes. A two-dimensional intermolecular PES was constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] plus aug-cc-pVQZ basis set supplemented with bond functions for each complex. The global minimum was assigned as the collinear structure of Ar–Ag–X, while the local minimum was assigned as the anti-linear structure of Ar–X–Ag. Both Ar–Ag and Ar–X distances display us an increasing trend from Ar–AgF to Ar–AgI complexes. Based on the bound state results, the intermolecular vibrational modes of collinear and anti-linear isomers were studied in detail via the wavefunction analysis. Due to the very low well depth for the anti-linear structure, an obvious delocalization effect was observed for each complex, except for Ar–AgI. Furthermore, our calculated results suggest that the anti-linear isomer of Ar–AgBr and Ar–AgI could be observed in experiment. The rotational energy levels were also determined based on the ab initio PESs via the bound state calculations. The microwave spectrum for the collinear isomer of each complex was predicted with the maximal percentage error of 1.55% for the complex Ar–AgF. A simple method of coordinate translation was used to re-interpolate the PES for each isotopomer to determine the isotope effects for Ar–AgX complexes and the deduced results are in good agreement with those of experimental observation. The microwave spectrum can be much better reproduced with an equivalent percentage error of 0.07% cm−1 for each isotopomer based on a scaled PES. Finally, we checked the effects of the basis set superposition error (BSSE) correction and core correlation, and found that the BSSE correction has great influence on the intermolecular interactions for the Ar–AgX complexes.

In this present work, combing density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we investigate a novel white light material 2,2′-(thiazolo[5,4-d]thiazole-2,5-diyl)bis(4-tert-butylphenol) (t-HTTH) about its dual intramolecular hydrogen bonding behaviors and relative excited state intramolecular proton transfer (ESIPT) process in detail. Via testing functional and basis set, the DFT//TDDFT/MPW1PW91/6–311+G(d,p) theoretical level has been decided in three kinds of solvents (cyclohexane (CYH), dichloromethane (DCM) and toluene (Tol)), which can well reappear experimental phenomenon. Exploring molecular electrostatic potential (MEP), primary bond lengths, bond angles and infrared (IR) vibrational spectra for t-HTTH system in both S0 and S1 states, we find the double hydrogen bonds O1-H2···N3 as well as O4-H5···N6 should be strengthened in the S1 state. Investigating the photo-excitation process, we find that the S0 → S1 transition corresponds to charge transfer, which provides the driving force for ESIPT. And analyses about frontier molecular orbitals (MOs) and relative energy gaps between HOMO and LUMO orbitals, we deduced the ESIPT process may occur more likely in nonpolar solvents. Constructing potential energy curves, we reveal that the ESIPT reaction results in the dynamic equilibrium in S1 state between forward and backward processes, which facilitates white light. We not only clarify the excited state hydrogen bond dynamical behavior of t-HTTH material, but also elaborate the ESIPT mechanism and explain previous experimental phenomenon reasonably.

Two high efficient excited state intramolecular proton transfer (ESIPT) compounds (i.e., 3-(5-([1,1′-biphenyl]-4-yl)oxazol-2-yl)-4′-(N,N-diphenylamino)-[1,1′-biphenyl]-4-ol (1) and 4′-(N,N-diphenylamino)-3-(5-(4′-(diphenylamino)-[1,1′-biphenyl]-4-yl)oxazol-2-yl)-5-methyl-[1,1′-biphenyl]-4-ol (2)) are explored theoretically. Based on DFT and time-dependent DFT (TDDFT) methods, we investigate the hydrogen bonding interactions and ESIPT mechanism. Via B3LYP/TZVP/IEFPCM (toluene) theoretical level, we reappear the experimental steady-state spectra, which demonstrate that the theoretical manner is reasonable and effective. Based on reduced density gradient (RDG) versus sign(λ2)ρ analyses, we confirm intramolecular hydrogen bond for both 1-enol and 2-enol. Investigating geometrical parameters and infrared (IR) vibrational spectra, we verify the O-H···N should be strengthened in the S1 state for 1-enol and 2-enol systems. Exploring frontier molecular orbitals (MOs) and charge density difference (CDD) maps, we find charge redistribution provides the tendency of ESIPT. The constructed potential energy curves demonstrate that the proton transfer should happen in the S1 state. Particularly, the low potential energy barriers of forward and backward ESIPT process for both 1 and 2 systems, the dynamical equilibrium could be verified, which means 1 and 2 systems should be potential for novel white light LEDs materials. This work not only explores and explains previous experimental phenomenon, but also makes a reasonable assignment about the ESIPT mechanism.

In this work, using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we theoretically explore the excited state dynamical process about a novel DHDA-23-00 system [Phys. Chem. Chem. Phys. 19 (2017) 28641-28646]. Combining electrostatic potential surface (EPS) and the reduced density gradient (RDG) methods, we can affirm the two intramolecular hydrogen bonds (O1-H2⋯O3 and O4-H5⋯O6) should be formed in the S0 state for DHDA-23-00. Exploring primary chemical structural changes (bond lengths and bond angles involved in hydrogen bonds) upon the photo-excitation, we verify these two hydrogen bonds are strengthening in the S1 state. In view of the infrared (IR) vibrational spectra, the phenomenon of strengthening O1-H2⋯O3 and O4-H5⋯O6 can be confirmed once again. Analyses about frontier molecular orbitals (MOs) in the excitation process, it can be found charge redistribution around hydroxide radical moiety could play important roles in enhancing intramolecular hydrogen bonds O1-H2⋯O3 and O4-H5⋯O6. Given this kind of charge transfer may facilitate excited state proton transfer (ESPT) process, we construct the potential energy surfaces (PESs) along with two hydrogen bonds to provide the excited state dynamical overall perspective. For DHDA-23-00, even though the charge transfer supports the ESPT process in acetonitrile solvent, excited state potential energy barriers confirm ESPT reaction does not occur for DHDA-23-00 system that is consistent with experimental phenomenon.

In this present work, we theoretically investigate the four HBO derivatives (i.e., HBO-NH2, HBO-OH, HBO-NO2, HBO-COOH) about their different excited state behaviors involved in excited state intramolecular proton transfer (ESIPT) process. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) theoretical level, we analyze the bond lengths, bond angles and relative chemical changes about these four structures. In addition, coupling with the infrared (IR) vibrational spectra, we confirm that the intramolecular hydrogen bond O1 H2···N3 in these four structures should be strengthened in the S1 state, which might provide the possibility for ESIPT reaction. Further, studying the vertical excitation process, we explore the charge redistribution and find that more charge would be transferred from HOMO to LUMO orbital for electron withdrawing groups (i.e., HBO-NO2 and HBO-COOH). In other words, electron withdrawing groups NO2 and COOH would facilitate the ESIPT reaction. Via constructing the potential energy curves of both S0 and S1 states, we further confirm that electron withdrawing substitutions could promote the ESIPT process for HBO systems. We believe that this present work not only elaborates the different excited state behaviors of HBO-NH2, HBO-OH, HBO-NO2 and HBO-COOH, but also plays important roles in designing and developing new materials and applications in future.

In this work, the excited state dynamical behavior of a novel π-conjugated dye 2,2′-((5-(2-(4-methoxyphenyl)ethenyl)-benzene-1,1-diyl)-bis-(nitrilomethylylidene)-diphenol) (C1) has been investigated. Two intramolecular hydrogen bonds of C1 are tested to pre-existing in the ground state via AIM and reduced density gradient. Using a time-dependent density functional theory (TDDFT) method, it has been substantiated that the intramolecular hydrogen bonds of C1 should be strengthened in the S1 state via analyzing fundamental bond length, bond angles, and corresponding infrared vibrational modes. The most obvious variation of these two hydrogen bonds is the O4–H5···N6 bond, which might play important roles in excited state behavior for the C1 system. Furthermore, based on electronic excitation, charge transfer could occur. Just due to this kind of charge re-distribution, two hydrogen bonds should be tighter in the first excited state, which is consistent with the variation of hydrogen bond lengths. Thus, the phenomenon of charge transfer is reasonable evidence for confirming the occurrence of the excited state proton transfer (ESPT) process in the S1 state. Our theoretically constructed potential energy surfaces of C1 show that excited state single proton transfer should occur along with the O4–H5···N6 hydrogen bond rather than the O1–H2···N3 bond. We not only clarify the ESIPT mechanism for C1 but put forward new affiliation and explain a previous experiment successfully.

Charge redistribution indicates the ESIPT tendency. Two different ESIPT mechanisms have been found in toluene and DMF. Solvent effects may control the excited‐state behavior of a‐QD.

The monolayer AlN is one of graphene-like 2D material. On the basis of density functional theory (DFT) calculations, the adsorption of CO2, CO, H2, N2, CH4, O2 and NO on the monolayer AlN was investigated. Due to the dipole moment of the Al-N bond, the gas molecules can be adsorbed directly on the AlN sheet. This avoids the problem about formation of metal clusters using metal decorated carbon nanostructures as gas storage materials. Among all the gas molecules, only CO2 on the AlN sheet has strong interaction with adsorption energy of 0.91 eV. While other gas molecules bind to the AlN sheet much weakly with the adsorption energy being less than 0.5 eV. Due to the charge transfer between gas molecules and the AlN sheet, the AlN sheet can be used to gas sensors for CO2, CO, H2, O2 and NO. Moreover, the AlN sheet can be taken potential applications as sorbent materials for CO2 separation and capture from gas mixture.

At the TD-B3LYP/TZVP/IEFPCM theory level, we have theoretically studied the excited-state intramolecular proton coupled charge transfer (ESIPCCT) process for both 4′-N,N-diethylamino-3-hydroxyflavone (3HFN) and 2-{[2-(2-hydroxyphenyl)benzo[d]oxazol-6-yl]methylene}malononitrile (diCN-HBO) molecules. Our calculated hydrogen bond lengths and angles sufficiently confirm that the intramolecular hydrogen bonds O1–H1⋯O2 and O1–H1⋯N1 formed at the S0 states of 3HFN and diCN-HBO should be significantly strengthened in the S1 state, which is further supported by the results obtained based on the analyses of infrared spectra shifts, molecular orbitals and charge density differences maps. The significant strengthening of intramolecular hydrogen bonds O1–H1⋯O2 and O1–H1⋯N1 upon photoexcitation should facilitate the ESIPCCT process of the two title molecules. The scanned potential energy curves and confirmed excited-state transition states for both 3HFN and diCN-HBO show that the proton can be easily transferred from O1 to O2 (N1 for diCN-HBO) through the strengthened intramolecular hydrogen bonds upon photoexcitation to the S1 state.

We constructed three potential energy surfaces (PESs) for the ground and excited states of each complex including He–CS2, Ne–CS2, and Ar–CS2, respectively. Based on these PESs, the bound state calculations were performed to determine the rotational levels of the ground and excited states. Combining the experimental spectroscopic parameters of ground state and the rotational level differences between the ground and excited states, we accurately predicted the infrared spectra in the ν1 and ν1 + ν3 regions of CS2 monomer. The determined spectroscopic parameters and transition frequencies are in excellent agreement with the available experimental data.

The excited-state intramolecular proton transfer (ESIPT) mechanism of a new compound (E)-1-((2,2-diphenylhydrazono)methyl)naphthalen-2-ol (EDMN) sensor, reported and synthesized by Mukherjee et al. [Sensors Actuat. B-Chem. 2014, 202, 1190], is investigated in detail theoretically. The calculations on primary bond lengths, bond angles, and the corresponding infrared (IR) vibrational spectra and hydrogen-bond energy involved in intramolecular hydrogen bond between the S0 and S1 states confirm that the intramolecular hydrogen bond is strengthened in the S1 state, which reveals the tendency of ESIPT reaction. The fact that the experimental absorption and emission spectra are well reproduced demonstrates the rationality and effectiveness of the time-dependent density functional theory (TDDFT) level of theory we adopt here. Furthermore, intramolecular charge transfer based on the frontier molecular orbitals (MOs) gives indication of the ESIPT reaction. The constructed potential energy curves of both the S0 and S1 states while keeping the O─H distance of EDMN fixed at a series of values are used to illustrate the ESIPT process. The lower barrier of ~3.934 kcal/mol in the S1 state potential energy curve (lower than the 8.254 kcal/mol in the S0 state) provides the transfer mechanism.

In this present work, we theoretically investigate the excited state dynamical mechanism of a novel sensor trans-2-[4′-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine (t-DMASIP-b). Within the framework of density functional theory (DFT) and time dependent DFT (TDDFT) methods, we reasonably repeat the experimental electronic spectra, which further confirm the theoretical level used in this work is feasible. Given the best complex model, two methanol (MeOH) solvent molecules should be connected with t-DMASIP-b forming t-DMASIP-b-MeOH complex in both ground state and excited state. Exploring the changes about bond lengths and bond angles involved in hydrogen bond wires, we find the O5-H6 ⋯ N7 one should be largely strengthened in the S1 state, which might facilitate the excited state intermolecular proton transfer (ESIPT) process. In addition, the analyses about infrared (IR) vibrational spectra also confirm this conclusion. The redistribution about charges distinguished via frontier molecular orbitals (MOs) based on the photo-excitation, we do find tendency of ESIPT reaction due to the most charges located around N7 atom in the LUMO orbital. Even though some indications reveal the ESIPT, we find the moderate potential energy barriers in the S1-state potential energy curves. The moderate potential energy barrier 12.89 kcal/mol along with O5-H6 ⋯ N7 hydrogen bonding wire indeed hinders the proceeding of ESIPT, so only one fluorescence peak was reported in previous experiment, which has been reasonably explained in our work. As a whole, we deem our work not only successfully explains previous experimental work, but also paves the way for the further applications about t-DMASIP-b sensor in future.

In this present work, adopting density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we theoretically research the excited state dynamical process about two imide compound N-cyclohexyl-3-hydroxyphthalimide (3HNHPI) and 3,6-Dihydroxy-N-cyclohexylphthalimide (DHNHPI). We find the intramolecular hydrogen bonds in these two systems should be strengthening in the S1 state, which may trigger excited state intramolecular proton transfer (ESIPT) reaction. Analysis about charge redistribution implies the tendency of ESIPT reaction for both 3HNHPI and DHNHPI. However the constructed potential energy surfaces confirm that the ESIPT process should occur for 3HNHPI rather than DHNHPI molecule, which is consistent with previous experiment [Phys. Chem. Chem. Phys. 17 (2015) 30659–30669]. Via transition state (TS) theory, we successfully account for the vague explanation in previous work and clarify that why the proton transfer reaction missing for DHNHPI in the S1 state.

A novel fluorescent probe 4′-fluoroflavonol (4F) was reported by Serdiuk et al. (RSC Adv 6:42532, 2016) in a previous paper. Spectroscopic studies on excited-state proton transfer (ESPT) of 4F was mentioned, while the mechanism of ESPT for 4F isdeficiency. In this present work, based on the time dependent density functional theory (TDDFT), we investigated the excited-state intramolecular proton transfer (ESIPT) mechanism of 4F theoretically. The primary bond lengths, bond angles and the infrared (IR) vibrational spectra involved in the formation of hydrogen bonds vertified the intramolecular hydrogen bond was strengthened, which manifests the tendency of excited state proton transfer. According to the results of calculated potential energy curves along O–H coordinate, an about 13.18 kcal/mol barrier has been found in the S0 state. However, a barrier of 3.29 kcal/mol was found in the S1 state, which demonstrates that the proton transfer process is more likely to occur in the excited state. In other words, the proton transfer was facilitated by photoexcitation. Particularly, the study about ESIPT mechanism of 4F should be helpful for further understanding property of fisetin.

A section of infrared spectrum for Xe–N 2 O has been recorded in the N 2 O monomer ν 1 region, but just 5 rotational resolved lines cannot make an effective rovibrational analysis. To improve the analysis of our observed spectrum for Xe–N 2 O, a new method is developed based on the bound state calculations with three ab initio potential energy surfaces (PESs). The accuracy of this method is validated by the excellent agreement between theoretical and experimental results for 152 rovibrational transition frequencies with a root mean square deviation of 0.00075 cm −1 and spectroscopic parameters with the deviation less than 0.6 MHz in the N 2 O monomer ν 3 region. The rotational constants for the excited state are derived with the values of A = 12716.1, B = 1075.2, C = 987.9 MHz in the ν 1 region of N 2 O monomer. The band origin of the spectrum is determined to be 1284.8760 cm −1 with a red shift of 0.0273 cm −1 compared with that of N 2 O monomer in the ν 1 region. The excellent agreement between experimental and theoretical results confirms that this new method is extremely helpful to make a rovibrational analysis for the infrared spectrum of van der Waals complex.

Recently, Piechowska and coworker found that hydroxybenzofluorenone 10-hydroxy11H-benzo[b]fluoren-11-one (10-HHBF) does not show dual fluorescence, which is in contrast to its well-known analogue 1-hydroxy-11H-benzo[b]fluoren-11-one (1-HHBF) [Dyes Pigm. 2019, 165, 346–353.]. Based on the increased donor-acceptor distance and the lower stability of the excited state tautomer of former, they believe that different from 1-HHBF, ESIPT is not occurring in 10-HHBF. In the preset work, in order to clarify whether ESIPT would take place in 10-HHBF, we have optimized the four-state geometrical structures (ground state S0, first singlet excited state S1, transition state S1-TS and after proton transfer S1-PT), carried out the Natural Population Analysis and scanned the ground-state and excited-state potential energy curves of 1-HHBF and 10-HHBF at TD-CAM-B3LYP/6–311 + g(2d,2p)/IEFPCM (cyclohexane) theory level. It is found that ESIPT should take place in both 1-HHBF and 10-HHBF and the Gibbs free energy diagram further indicates that the ESIPT process is more favorable in 10-HHBF than in 1-HHBF.

In this work, we have studied the isotope effects for the He–CO2 and Ne–CO2 complexes by means of theoretical calculations and experimental measurements, which were carried out using a distributed quantum cascade laser to probe a pulsed supersonic jet expansion. Firstly, infrared spectra have been recorded for the He/Ne–12C18O2 complexes. Spectroscopic parameters including band origin ν0, rotational constants A, B, C, and centrifugal distortion constants ΔJK were obtained by fitting a Watson A-reduced Hamiltonian with 13 assigned rovibrational transitions for He–12C18O2. For Ne–12C18O2, the observed spectrum produces a set of spectroscopic parameters including the band origin, rotational constants and all the quartic centrifugal distortion constants with more than 100 rovibrational transitions (40 new transitions). Secondly, we have calculated the rovibrational energy levels, vibrational shifts, and rotational constants for the He/Ne–CO2 complexes based on potential energy surfaces (PESs) and bound state calculations for ground and vibrationally excited states. The obtained results show that the spectroscopic characteristics (vibrational shifts and rotational constants) for Ne–CO2 are analogous to those of Ar–CO2, while those for He–CO2 show some differences especially for the rotational constants. Finally, according to the available experimental data and our theoretical calculations, infrared spectra were predicted for six isotopologues with C2v symmetry of Ne–CO2 complex.

By applying density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we theoretically investigate the excited state dynamical process for the 2,2′-((1E,1′E)-((3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl)-bis(azanylylidene))bis(methanylylidene))-diphenol (YT) system. Our results show that two intramolecular hydrogen bonds in YT strengthen in the S1 state, which may trigger an excited state proton transfer (ESPT) process. By exploring the frontier molecular orbitals (MOs), we confirm that charge redistribution indeed has effects on excited state dynamical behavior. Furthermore, this implies the tendency of the ESPT reaction. Analyzing the constructed S1-state potential energy surface (PES), we find three excited state potential barriers which are low enough for a complete excited state double proton transfer (ESDPT) process. Comparing barriers, we confirm a competitive process for stepwise and simultaneous ESDPT pathways.

In this study, within the framework of density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we theoretically investigated the novel system 2-phenylimidazo[4,5-b]pyridine (PIP) with respect to the dynamical behavior of its excited state in methanol (MeOH) solvents. Herein, two hydrogen-bonded networks have been discussed between PIP and MeOH, and it has been found that two MeOH connected to PIP (PIP–2MeOH) should be the best arrangement in both S0 and S1 states. Investigations on the electronic spectra of PIP–2MeOH have verified this point. Via analysis of hydrogen bond wires and corresponding infrared (IR) vibrational spectra, we have found that N1–H2⋯O3 of PIP–2MeOH undergoes the biggest change upon photoexcitation that reflects the tendency of the excited state intermolecular proton transfer (ESIPT) process. According to the results of our theoretical potential energy curves along different coordinates, we confirmed that ESIPT reaction should occur along the hydrogen bond wire N1–H2⋯O3 first. After the ESIPT reaction, proton transfer of PIP–2MeOH-PT* could proceed via intersystem crossing (ISC) process from S1 state to T1 state with a negligible energy gap 0.031 eV. Due to this non-radiation process, the fluorescence peak of PIP–2MeOH-PT* could be quenched. Our study not only explains previous successful experiment, but also proposes a new excited state dynamical mechanism for the PIP system.

In the present work, we theoretically study and elaborate the excited state proton transfer (ESPT) behavior of two novel polyimides (3H-MC and P2H-CH) reported in the previous work [K. Kanosue, T. Shimosaka, J. Wakita and S. Ando, Macromolecules, 2015, 48, 1777; K. Kanosue, R. Augulis, D. Peckus, R. Karpicz, T. Tamulevicius, S. Tamulevicius, V. Gubinas and S. Ando, Macromolecules, 2016, 49, 1848]. Using density functional theory (DFT) and time-dependent DFT (TDDFT) methods with electrostatic potential surfaces and the reduced density gradient (RDG), we affirm that an intramolecular hydrogen bond should be formed in the ground state for these two systems. Comparing bond lengths, bond angles and the corresponding infrared (IR) vibrations of intramolecular hydrogen bonds for 3H-MC and P2H-CH, we clarify that hydrogen bonds should be strengthened in the S1 state, which provides the possibility for the excited state intramolecular proton transfer (ESIPT) reaction. Analyses of frontier molecular orbitals (MOs) theory prove that the ESIPT process could be facilitated by charge transfer upon excitation. Based on constructing potential energy surfaces (PESs), we provide the excited state dynamical overall perspective about ESIPT reactions for both 3H-MC and P2H-CH. We not only clarify the ESPT mechanism of these two systems, but also make contributions for the applications of such kinds of systems in the future.

The properties of intramolecular hydrogen bond of a new photochemical sensor 4'-N,N-dimethylamino-3-hydroxyflavone (dmahf) has been investigated in detail. Using Atoms-In-Molecule method, we have demonstrated that the intramolecular hydrogen bond was formed in the ground state (S-0 state). The calculated dominating bond lengths and angles involved in hydrogen bond demonstrates that the intramolecular hydrogen bond can be strengthened in the first excited state (S-1 state). In addition, the variation of hydrogen bond of dmahf has been also testified based on infrared vibrational spectra. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer process. According to the calculated results of potential energy curves along O-H coordinate, the potential energy barrier of about 7.49 kcal/mol is discovered in the S-0 state. However, a lower potential energy barrier of 1.61 kcal/mol has been found in the S-1 state, which demonstrates that the proton transfer process is more likely to happen in the S-1 state than the S-0 state. In other words, the proton transfer reaction can be facilitated based on the photoexcitation effectively. In turn, through the process of radiative transition, the proton-transfer form dmahf-keto regresses to the ground state with the fluorescence of 578 nm.

In this work, DFT and TDDFT approaches are performed to make a detailed exploration about excited state behavior for 2-Benzothiazol-2-yl-4-methoxy-6-(1,4,5-triphenyl-4,5-dihydro-1H-imidazol-2-yl)-phenol (BTImP) system. Combining geometrical parameters and theoretical infrared analyses, we prove hydrogen bond of BTImP is strengthening in S1 state. Insights into frontier molecular orbitals, we present charge redistribution facilitates excited state intramolecular proton transfer (ESIPT) reaction. Probing into potential energy curves, we confirm the ultrafast ESIPT mechanism for BTImP. Furthermore, given different solvent polarities, we deem the ESIPT behavior of BTImP could be controlled. We wish this work could facilitate developing novel sensors in future.

By applying DFT and TDDFT methods, we probe into excited state luminescent properties as well as intramolecular proton transfer (ESIPT) process for a novel 5-(diethylamino)-2-(((6-methoxybenzo[d]thiazol-2-yl)imino)methyl)phenol (DMBYMP) system. We affirm intramolecular hydrogen bond of DMBYMP is supposed to become enhanced in S1. Exploring vertical excitation and charge redistribution, intramolecular charge transfer property has been found that triggers ESIPT reaction. We further construct potential energy curves and present the ultrafast ESIPT mechanism for DMBYMP. We sincerely wish this work could play roles in further developing novel applications based on DMBYMP compound and in promoting new ratiometric fluorescence probes in future.

In view of their facile synthetic routes and remarkable photo-induced stabilities, excited state intramolecular proton-transfer (ESIPT)-vibrant luminous materials have drawn more and more attention...

The excited-state intramolecular proton transfer (ESIPT) reaction in 1-hydroxy-11H-benzo[b]fluoren-11-one (HBF) is found to be highly sensitive to the presence of specific substituents in positions C2, C4 and C8 with respect to the hydroxyl group, leading to different fluorescent behaviors of HBF with different substituents (J. Phys. Chem. C, 2018, 122, 21833). However, a systematic and comprehensive computational study of the influence of alkyl-substitutions at various positions of HBF on the intramolecular hydrogen bond strength, adsorption and fluorescence spectra and finally the proton transfer energy barriers is scare up to now. Therefore, in this work, the excited-state overall perspective of the proton transfer process of HBF and its seven tert-butyl substituted derivatives (Scheme 1) have been theoretically studied at TD-PBE0/TZVP theory level with the DFT and TDDFT methods. It is concluded that alkyl-substitution at positions C2 and C4 of the parent molecule should increase the strength of intramolecular hydrogen bonding O1-H⋯O, which decrease both the S1-state forward proton transfer energy barriers and the energy differences between forms S1-PT and S1 and eventually facilitate the ESIPT process, whereas alkyl-substitution at position C8 of the parent molecule should have slight opposite effect.

In this work we report an ab initio intermolecular potential energy surface and theoretically spectroscopic studies for N2–OCS complex. A four-dimensional intermolecular potential energy surface (4D PES) is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum corresponding to a planar and nearly T-shaped structure, which has been observed experimentally, is located at R = 3.96 A, θ1 = 8 or 172°, θ2 = 75°, φ = 180 or 0° with a well depth of 271.078 cm−1 on the potential energy surface. The local minimum corresponding to a linear geometry is also found at R = 5.06 A, θ1 = 2 or 178°, θ2 = 179°, φ = 0 or 180° with a well depth of 224.743 cm−1. The bound state calculations have been performed for the complex by approximating the N2 and OCS molecules as the rigid rotors. The calculated structural parameters and rotational transition frequencies are in good agreement with the experimental observed values. Based on the ab initio PES, the tunneling splitting is calculated to be 0.052 cm−1 for the ground vibrational state, which can just reproduce 64% of experimental observation (0.082 cm−1). A refined method is used to calculate the tunneling splitting, and a much better result is obtained with the value of 0.094 cm−1.

Based on density functional theory calculations, we studied the Li dispersed on porous graphene (PG) for its application as Li ion battery anode material. The hybridization of Li atoms and the carbon atoms enhanced the interaction between Li atoms and the PG. With holes of specific size, the PG can provide excellent mobility with moderate barriers of 0.37–0.39 eV. The highest Li storage composite can be LiC0.75H0.38 which corresponds to a specific capacity of 2857.7 mA h/g. Both specific capacity and binding energy are significantly larger than the corresponding value of graphite, this makes PG a promising candidate for the anode material in battery applications. The interactions between the Li atoms and PG can be easily tuned by an applied strain. Under biaxial strain of 16%, the binding energy of Li to PG is increased by 17% compared to its unstrained state.

The time-dependent density functional theory (TDDFT) method has been carried out to investigate the hydrogen bonding dynamics of a series of hydrogen-bonded complexes of PYP chromophore formed with water molecules both in vacuum and aqueous solution. We demonstrate that the intermolecular hydrogen bonds formed between carbonyl oxygen and hydrogen of water are strengthened in the lowest bright state as well as one other charge transfer state and result in spectral redshift. Whereas, a totally opposite result happens to the site of phenolate oxygen, which can be confirmed based on the excited-state geometric optimizations by TDDFT method. In addition, the frontier molecular orbital analysis reveals the nature of the lowest bright state and the CT state as well as the understanding of the electronic excited-state hydrogen bonding dynamics. Moreover, two approaches are adopted to consider the solvation effect.

In this work, the excited-state spectral and dynamic properties of the two intermolecular hydrogen-bonded complexes formed by 4-(dimethylamino)cinnamic acid (abbreviated as DMACA) with water molecules have been studied using the time-dependent density functional theory (TDDFT) method. For the hydrogen-bonded complex formed at the carboxy group of DMACA, no obvious influence was found on the photochemical and photophysical processes of DMACA. However, for the hydrogen-bonded complex formed at the nitrogen atom of DMACA, the situation is quite different. The intermolecular hydrogen bond at the nitrogen atom is significantly weakened in the S1 state, which obviously enhances the S0–S1 excitation energy and explains the much larger blueshift of the absorption spectrum peak of DMACA in protonic solvents such as water. Additionally, the intermolecular hydrogen bond at the nitrogen atom directly affects the hybrid form of the nitrogen atom, which results in the obvious changes of the DMACA structure in both ground and excited states. Moreover, based on the comparisons of the S0–Sn and S0–Tn excitation energies, a new radiationless deactivation path, S1 → T2 → T1, is proposed for DMACA in protonic solvents, which sheds light on the obvious decrease of the fluorescence quantum yield of DMACA in water.

Spectroscopic investigations on excited state proton transfer of a new dibenzimidazolo diimine sensor (DDS) were reported by Goswami et al. recently. In our present work, based on the time-dependent density functional theory (TDDFT), the excited-state intramolecular proton transfer (ESIPT) mechanism of DDS is studied theoretically. Our calculated results reproduced absorption and fluorescence emission spectra of the previous experiment, which verifies that the TDDFT method we adopted is reasonable and effective. The calculated dominating bond lengths and bond angles involved in hydrogen bond demonstrate that the intramolecular hydrogen bond is strengthened. In addition, the phenomenon of hydrogen bond reinforce has also been testified based on infrared vibrational spectra. Further, hydrogen bonding strengthening manifests the tendency of ESIPT process. The calculated frontier molecular orbitals further demonstrate that the excited state proton transfer is likely to occur. According to the calculated results of potential energy curves along O–H coordinate, the potential energy barrier of about 5.02 kcal/mol is discovered in the S0 state. However, a lower potential energy barrier of 0.195 kcal/mol is found in the S1 state, which demonstrates that the proton transfer process is more likely to happen in the S1 state than the S0 state. In other words, the proton transfer reaction can be facilitated based on the photo-excitation effectively. Moreover, the phenomenon of fluorescence quenching could be explained based on the ESIPT mechanism. Copyright © 2015 John Wiley & Sons, Ltd.

In this present work, we theoretically investigate the excited state mechanism for the 2-(phenyl)imidazo[4,5-c]pyridine (PIP-C) molecule combined with methanol (MeOH) solvent molecules. Three MeOH molecules should be connected with PIP-C forming stable PIP-C-MeOH complex in the S0 state. Upon the photo-excitation, the hydrogen bonded wires are strengthened in the S1 state. Particularly the deprotonation process of PIP-C facilitates the excited state intermolecular proton transfer (ESIPT) process. In our work, we do verify that the ESIPT reaction should occur due to the low potential energy barrier 8.785 kcal/mol in the S1 state. While the intersection of potential energy curves of S0 and S1 states result in the nonradiation transition from S1 to S0 state, which successfully explain why the emission peak of the proton-transfer PIP-C-MeOH-PT form could not be reported in previous experiment. As a whole, this work not only put forward a new excited state mechanism for PIP-C system, but also compensates for the defects about mechanism in previous experiment.

In the current study, we offer our first-principles calculations on monolayer VS2 as hosting material of cathode for Li-S battery. The results show that the Li2Sn molecules are captured by VS2 with an appropriate adsorption energy ranging from 1.13 eV to 4.44 eV, indicating that VS2 can trap LiPSs stably and effectively through van der Waals and charge transfer mechanisms, which could suppress the shuttle effect. The diffusion of Li atom on VS2 shows a small barrier energy of 0.25 eV. Therefore, VS2 might be a promising anchoring material for Li-S batteries.

In this work, the ESIPT mechanism of the novel HDPB compound is investigated. Probing into non-hydrogen bonding HDPB-O, we verify the stabilization of hydrogen bond. Based on simulating geometrical changes, we present O H⋯N of HDPB is enhanced by photoexcitation. Exploring MOs, we present charge recombination facilitates attracting proton, which promotes ESIPT tendency. Constructing potential energy curves (PECs) for HDPB, the low potential barrier 2.2107 kcal/mol is found for ESIPT process. Due to the low barrier, ultrafast ESIPT reaction occurs. It explains the non-fluorescent phenomenon of HDPB itself. This work clarifies ESIPT mechanism for HDPB, but also explains experimental phenomenon.

This study is a continuation of our previously published research for the N2–N2O complex [Journal of Chemical Physics 143 (2015) 154304], and focuses on predicting the quantum tunneling effects of infrared fundamental and combination bands. A new four-dimensional intermolecular potential energy surface (PES) was constructed for the vibrational excited state upon the N2O ν1 excitation at the same calculated level with the previous PES of ground state. Compared with the ground state, two equivalent T-shaped global minima are found to be slightly different in both structural parameters and binding energies. Based on the PESs of ground and vibrational excited states, the vibrational shift of infrared spectrum for the fundamental band in the N2O ν1 region is determined to be a blue shift of 1.29 cm−1 for 14N2–N2O, which is in qualitative agreement with the experimentally observed value of 2.233 cm−1 [Journal of Chemical Physics 140 (2014) 044332]. Furthermore, for the fundamental and disrotation bands, the calculated tunneling splitting is almost the same for the ground and vibrational excited states, so the tunneling effects cannot be observed for these bands using the infrared spectroscopic technique. Nevertheless for the infrared combination bands, our calculated results suggest that the tunneling effects for the torsion and twice disrotation bands are significantly larger, and the predicted infrared spectra display obvious differences for the different sub-states. If the sensitivity of infrared spectrometer is high enough, it is interesting to investigate the quantum tunneling effects experimentally.

Given the importance of excited state relaxation in photochemical and photophysical behaviours, in this work, we mainly focus on the excited state dynamical behaviours for the novel 6-cyano-2-(2′-hydroxyphenyl)imidazo[1,2a]pyridine (6-CN-HPIP) system in different aprotic solvents. We find the ultrafast excited state intramolecular proton transfer (ESIPT) behaviour without potential energy barrier for 6-CN-HPIP in nonpolar solvents. Furthermore, we also explore the excited state intramolecular hydrogen bonding interactions and confirm the hydrogen bond O-H⋯N of 6-CN-HPIP should be strengthened based photo-excitation process. It provides the possibility of ESIPT process. And the charge redistribution resulting from photo-excitation around hydrogen bonding moieties further reveals the ESIPT tendency for 6-CN-HPIP molecule. It is worth mentioning that the increased electronic densities around proton-acceptor moiety play important roles in attracting hydrogen proton, which directly promotes ESIPT reaction. Via constructing potential energy curves, we clarify the ESIPT dynamical process for 6-CN-HPIP system and present a novel mechanism that nonpolar aprotic solvents facilitate ESIPT behaviour for 6-CN-HPIP. We hope that novel applications and developments could be promoted for 6-CH-HPIP and its derivatives through regulating and controlling ESIPT behaviours in future.