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1.
J Phys Chem Lett ; 12(39): 9710-9719, 2021 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-34590858

RESUMO

The time-resolved polarization-sensitive transient-absorption (TA) pump-probe (PP) spectra are simulated using on-the-fly surface-hopping nonadiabatic dynamics and the doorway-window representation of nonlinear spectroscopy. A dendrimer model system composed of two linear phenylene ethynylene units (2-ring and 3-ring) is taken as an example. The ground-state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions as well as the total TA PP signals are obtained and carefully analyzed. It is shown that intramolecular excited-state energy transfer from the 2-ring unit to the 3-ring unit can be conveniently identified by employing pump and probe pulses with different polarizations. Our results demonstrate that time-resolved polarization-sensitive TA PP signals provide a powerful tool for the elucidation of excited-state energy-transfer pathways, notably in molecular systems possessing several optically bright nonadiabatically coupled electronic states with different orientations of transition dipole moments.

2.
Front Chem ; 9: 740018, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34552914

RESUMO

Purely aromatic hydrocarbon materials with ultralong room-temperature phosphorescence (RTP) were reported recently, but which is universally recognized as unobservable. To reveal the inherent luminescent mechanism, two compounds, i.e., PT with a faint RTP and HD with strong RTP featured by nonplanar geometry, were chosen as a prototype to study their excited-state electronic structures by using quantum mechanics/molecular mechanics (QM/MM) model. It is demonstrated that the nonplanar ethylene brides can offer σ-electron to strengthen spin-orbit coupling (SOC) between singlet and triplet excited states, which can not only promote intersystem crossing (ISC) of S1→Tn to increase the population of triplet excitons, but also accelerate the radiative decay rate of T1→S0, and thus improving RTP. Impressively, the nonradiative decay rate only has a small increase, owing to the synergistic effect between the increase of SOC and the reduction of reorganization energy of T1→S0 caused by the restricted torsional motions of aromatic rings. Therefore, a bright and long-lived RTP was obtained in aromatic hydrocarbon materials with twisted structure. This work provided a new insight into the ultralong RTP in pure organic materials.

3.
Phys Chem Chem Phys ; 2021 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-34546246

RESUMO

The photolysis mechanism of methyl nitrate (CH3ONO2) was studied using the on-the-fly surface hopping dynamics at the XMS-CASPT2 level. Several critical geometries, including electronic state minima and conical intersections, were obtained, which play essential roles in the nonadiabatic dynamics of CH3ONO2. The ultrafast nonadiabatic decay dynamics to the ground state were simulated, which gives a proper explanation on the broad and structureless absorption spectra of CH3ONO2. The photodissociation channels, including CH3O + NO2, CH3O + NO + O, and others, as well as their branching ratios, were identified. When the dynamics starts from the lowest two electronic states (S1 and S2), the CH3O + NO2 channel is the dominant photolysis pathway, although we observed the minor contributions of other channels. In contrast, when the trajectories start from the third excited state S3, both CH3O + NO2 and CH3O + NO + O channels become important. Here the CH3O-NO2 bond dissociation takes place first, and then for some trajectories, the N-O bond of the NO2 part breaks successively. The quasi-degeneracy of electronic states may exist in the dissociation limits of both CH3O + NO2 and CH3O + NO + O channels. The current work provides valuable information in the understanding of experimental findings of the wavelength-dependent photolysis mechanism of CH3ONO2.

4.
Angew Chem Int Ed Engl ; 60(40): 21918-21926, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34309164

RESUMO

The first example of luminescent monosubstituted polyacetylenes (mono-PAs) is presented, based on a contracted cis-cisoid polyene backbone. It has an excellent circularly polarized luminescence (CPL) performance with a high dissymmetric factor (up to the order of 10-1 ). The luminescence stems from the helical cis-cisoid PA backbone, which is tightly fixed by the strong intramolecular hydrogen bonds, thereby reversing the energy order of excited states and enabling an emissive energy dissipation. CPL switches are facilely achieved by the solvent and temperature through reversible conformational transition. By taking advantages of fast response and high sensitivity, the thin film of mono-PAs could be used as a CPL-based probe for quantitative detection of trifluoroacetic acid with a wider linear dynamic range than those of photoluminescence and circular dichroism. This work opens a new avenue to develop novel smart CPL materials through modulating conformational transition.

5.
Angew Chem Int Ed Engl ; 60(37): 20498-20503, 2021 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-34319641

RESUMO

Efficient organic emitters in the deep-red region are rare due to the "energy gap law". Herein, multiple boron (B)- and nitrogen (N)-atoms embedded polycyclic heteroaromatics featuring hybridized π-bonding/ non-bonding molecular orbitals are constructed, providing a way to overcome the above luminescent boundary. The introduction of B-phenyl-B and N-phenyl-N structures enhances the electronic coupling of those para-positioned atoms, forming restricted π-bonds on the phenyl-core for delocalized excited states and thus a narrow energy gap. The mutually ortho-positioned B- and N-atoms also induce a multi-resonance effect on the peripheral skeleton for the non-bonding orbitals, creating shallow potential energy surfaces to eliminate the high-frequency vibrational quenching. The corresponding deep-red emitters with peaks at 662 and 692 nm exhibit narrow full-width at half-maximums of 38 nm, high radiative decay rates of ca. 108  s-1 , ≈100 % photo-luminescence quantum yields and record-high maximum external quantum efficiencies of ca. 28 % in a normal planar organic light-emitting diode structure, simultaneously.

6.
Chemosphere ; 281: 130831, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34289597

RESUMO

The understanding of the photochemistry of antibiotic compounds is important because it gives the direct information on the possible environmental pollution caused by them. Due to their large size, the theoretical studies of their excited-state reactions are rather challenging. In current work, we combined the on-the-fly trajectory surface-hopping dynamics, conical-intersection optimizations and excited-state pathway calculations to study the photochemistry of the trans-isomer of nitrofurantoin, a widely-used drug to treat the urinary tract infections. The dynamics-then-pathway approach was taken. First the trajectory surface hopping dynamics at the state-averaged complete-active-space self-consistent-field (SA-CASSCF) level with small active space and small basis sets were run. Second, the minimum-energy conical-intersection optimizations were performed. Finally the excited pathways from the Frank-Condon region to different reaction channels were built at the multi-state multi-reference second-order perturbation (MS-CASPT2) level with large active space and large basis set. Several possible channels responsible for the photo-induced reaction mechanism of the trans-nitrofurantoin were obtained, including the cleavage of the NO bond of the NO2 moiety, the photoisomerization at the central CN bond, and other internal conversion channels. Our findings give some preliminary explanations on available experimental observations. It is also demonstrates that the current theoretical approach is a powerful tool to explore the excited-state reactions in the photochemistry of media-sized or large-sized drug compounds.


Assuntos
Nitrofurantoína , Teoria Quântica , Isomerismo , Modelos Teóricos , Fotoquímica
7.
J Chem Theory Comput ; 17(6): 3267-3279, 2021 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-34028268

RESUMO

The on-the-fly version of the symmetrical quasi-classical dynamics method based on the Meyer-Miller mapping Hamiltonian (SQC/MM) is implemented to study the nonadiabatic dynamics at conical intersections of polyatomic systems. The current on-the-fly implementation of the SQC/MM method is based on the adiabatic representation and the dressed momentum. To include the zero-point energy (ZPE) correction of the electronic mapping variables, we employ both the γ-adjusted and γ-fixed approaches. Nonadiabatic dynamics of the methaniminium cation (CH2NH2+) and azomethane are simulated using the on-the-fly SQC/MM method. For CH2NH2+, both ZPE correction approaches give reasonable and consistent results. However, for azomethane, the γ-adjusted version of the SQC/MM dynamics behaves much better than the γ-fixed version. Further analysis indicates that it is always recommended to use the γ-adjusted SQC/MM dynamics in the on-the-fly simulation of photoinduced dynamics of polyatomic systems, particularly when the excited state is well separated from the ground state in the Franck-Condon region. This work indicates that the on-the-fly SQC/MM method is a powerful simulation protocol to deal with the nonadiabatic dynamics of realistic polyatomic systems.

8.
J Chem Phys ; 154(9): 094122, 2021 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-33685149

RESUMO

The system-plus-bath model is an important tool to understand the nonadiabatic dynamics of large molecular systems. Understanding the collective motion of a large number of bath modes is essential for revealing their key roles in the overall dynamics. Here, we applied principal component analysis (PCA) to investigate the bath motion in the basis of a large dataset generated from the symmetrical quasi-classical dynamics method based on the Meyer-Miller mapping Hamiltonian nonadiabatic dynamics for the excited-state energy transfer in the Frenkel-exciton model. The PCA method clearly elucidated that two types of bath modes, which either display strong vibronic coupling or have frequencies close to that of the electronic transition, are important to the nonadiabatic dynamics. These observations were fully consistent with the physical insights. The conclusions were based on the PCA of the trajectory data and did not involve significant pre-defined physical knowledge. The results show that the PCA approach, which is one of the simplest unsupervised machine learning dimensionality reduction methods, is a powerful one for analyzing complicated nonadiabatic dynamics in the condensed phase with many degrees of freedom.

9.
Angew Chem Int Ed Engl ; 59(40): 17499-17503, 2020 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-32618031

RESUMO

Pure green emitters are essential for realizing an ultrawide color gamut in next-generation displays. Herein, by fusing the difficult-to-access aza-aromatics onto B (boron)-N (nitrogen) skeleton, a hybridized multi-resonance and charge transfer (HMCT) molecule AZA-BN was successfully synthesized through an effective one-shot multiple cyclization method. AZA-BN shows pure green fluorescence with photoluminance quantum yield of 99.7 %. The corresponding green device exhibits a maximum external quantum efficiency and power efficiency of 28.2 % and 121.7 lm W-1 , respectively, with a full width half maximum (FWHM) of merely 30 nm and Commission Internationale de l'Eclairage (CIE) coordinate y of 0.69, representing the purest green bottom-emitting organic light-emitting diode.

10.
J Sep Sci ; 43(8): 1423-1430, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32003152

RESUMO

An online high-pH reversed-phase liquid chromatography× low-pH reversed-phase liquid chromatography tandem electrospray ionization mass spectrometry combined with pulse elution gradient in the first dimension was constructed to separate and identify alkaloids from Macleaya cordata (willd.) R. Br. The modulation was performed by using a dual second dimensional columns interface combined with a make-up dilution pump, which is responsible for dilution and neutralization of the first dimensional effluent, and the dual second dimensional columns integrated the trapping and the separation function to reduce the second dimension system dead volume. Taking advantage of the dissociable characteristics of alkaloids, mobile phases with different pH values were applied in the first dimension (pH 9.0) and the second dimension (pH 2.6) to improve the orthogonality of two-dimension separation. Besides, the pulse elution gradient in first dimension and second dimensional gradient were carefully optimized and much better separation was achieved compared to the separation with the traditional two-dimensional liquid chromatography approach. Finally, mass measurement was performed for alkaloids in M. cordata (willd.) R. Br. by coupling proposed two-dimensional liquid chromatography system with triple quadrupole mass spectrometry, and 39 alkaloids were successfully identified by comparing the obtained result with the former reported results.


Assuntos
Alcaloides/análise , Papaveraceae/química , Cromatografia Líquida , Cromatografia de Fase Reversa , Concentração de Íons de Hidrogênio , Espectrometria de Massas por Ionização por Electrospray
11.
J Chem Phys ; 150(16): 164126, 2019 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-31042919

RESUMO

We carried out extensive studies to examine the performance of the fewest-switches surface hopping method in the description of the ultrafast intersystem crossing dynamic of various singlet-triplet (S-T) models by comparison with the results of the exact full quantum dynamics. Different implementation details and some derivative approaches were examined. As expected, it is better to perform the trajectory surface hopping calculations in the spin-adiabatic representation or by the local diabatization approach, instead of in the spin-diabatic representation. The surface hopping method provides reasonable results for the short-time dynamics in the S-T model with weak spin-orbital coupling (diabatic coupling), although it does not perform well in the models with strong spin-orbital coupling (diabatic coupling). When the system accesses the S-T potential energy crossing with rather high kinetic energy, the trajectory surface hopping method tends to produce a good description of the nonadiabatic intersystem crossing dynamics. The impact of the decoherence correction on the performance of the trajectory surface hopping is system dependent. It improves the result accuracy in many cases, while its influence may also be minor for other cases.

12.
J Chromatogr A ; 1583: 98-107, 2019 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-30477714

RESUMO

In this work, a reversed phase liquid chromatography (RPLC) coupling to hydrophilic interaction chromatography (HILIC) system has been constructed, combining with pulsed elution reversed phase liquid chromatography (PE-RPLC) and HILIC to comprehensively analyze P. ginseng root extract, which is rich in saponins. By the application of pulsed elution (PE) modulation technique, the proposed RPLC × HILIC system allows the chromatographic separation to be optimized independently in both dimensions. In the first dimension (1D), PE modulation is achieved by the separation of a complex mixture, such as P. ginseng root extract, with a PE gradient. This PE gradient contains a set of pulses where the solvent strength increases gradually. Thus, the modulation of 1D eluent is realized by stepwise-pulse fractionation, rather than by a traditional two-dimensional interface. Furthermore, the number of fractions and the fractionated period can be regulated independently, which leads to independent adjustment of the separation cycle in the second dimension (2D) separation without the loss of D1 separation efficiency. To overcome the inherent solvent incompatibility of RPLC × HILIC, we introduced a newly developed trapping interface, equipped with bypass. The result indicates excellent separation of saponins in P. ginseng root extract. Compared with the traditional modulation method, the proposed RPLC × HILIC system has extreme flexibility, those modulation time could be regulated in a large range without re-optimizing the 1D PE gradient. Worthily mentioned, the proposed RPLC × HILIC system shows excellent orthogonality, and 20% more peaks could be obtained with current method compared to the traditional value based modulation method. Independent regulation of both dimensions could enable the proposed modulation method to be widely applied for complex samples analysis in ordinary laboratory.


Assuntos
Cromatografia Líquida/métodos , Cromatografia de Fase Reversa/métodos , Interações Hidrofóbicas e Hidrofílicas , Sistemas On-Line , Fracionamento Químico , Hidrocarbonetos Aromáticos/análise , Panax/química , Extratos Vegetais/química , Raízes de Plantas/química , Saponinas/análise
13.
Phys Chem Chem Phys ; 20(40): 25910-25917, 2018 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-30289421

RESUMO

Unidirectional rotation represents a very important functional feature in photochemistry, such as in the design of light-driven molecular rotary motors. Great attention has recently been devoted to the unidirectional preference of the torsional motion of azobenzene and other molecules. Azoheteroarenes offer functional advantages over their more conventional azobenzene counterparts due to the introduction of heteroaromatic rings. In this paper, the Z-E photoisomerization dynamics of two azoheteroarenes, 1,2-bis(1-methyl-1H-imidazol-2-yl)diazene and 1,2-bis(1H-imidazol-2-yl)diazene, are investigated with trajectory surface-hopping molecular dynamics at the semi-empirical OM2/MRCI level. Starting from the S1 excited state of the M-helical Z-isomer of both azoheteroarenes, more than 99% of the trajectories decay to their ground states through the M-helical conical intersections by twisting about the central N[double bond, length as m-dash]N double bond. This chiral path preference can be well understood by the energy profiles generated by the linear interpolation between the Franck-Condon geometry of the M-helical Z-isomer and the relevant S1/S0 conical intersections. The Z-E photoisomerization mechanisms of these two azoheteroarenes display a higher preference for unidirectional rotary dynamics under a chiral path than their counterpart azobenzene.

14.
J Phys Chem Lett ; 9(11): 2725-2732, 2018 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-29732893

RESUMO

We discuss a theoretical approach that employs machine learning potential energy surfaces (ML-PESs) in the nonadiabatic dynamics simulation of polyatomic systems by taking 6-aminopyrimidine as a typical example. The Zhu-Nakamura theory is employed in the surface hopping dynamics, which does not require the calculation of the nonadiabatic coupling vectors. The kernel ridge regression is used in the construction of the adiabatic PESs. In the nonadiabatic dynamics simulation, we use ML-PESs for most geometries and switch back to the electronic structure calculations for a few geometries either near the S1/S0 conical intersections or in the out-of-confidence regions. The dynamics results based on ML-PESs are consistent with those based on CASSCF PESs. The ML-PESs are further used to achieve the highly efficient massive dynamics simulations with a large number of trajectories. This work displays the powerful role of ML methods in the nonadiabatic dynamics simulation of polyatomic systems.

15.
J Chem Phys ; 149(24): 244104, 2018 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-30599730

RESUMO

We propose an "automatic" approach to analyze the results of the on-the-fly trajectory surface hopping simulation on the multi-channel nonadiabatic photoisomerization dynamics by considering the trajectory similarity and the configuration similarity. We choose a representative system phytochromobilin (P Φ B) chromophore model to illustrate the analysis protocol. After a large number of trajectories are obtained, it is possible to define the similarity of different trajectories by the Fréchet distance and to employ the trajectory clustering analysis to divide all trajectories into several clusters. Each cluster in principle represents a photoinduced isomerization reaction channel. This idea provides an effective approach to understand the branching ratio of the multi-channel photoisomerization dynamics. For each cluster, the dimensionality reduction is employed to understand the configuration similarity in the trajectory propagation, which provides the understanding of the major geometry evolution features in each reaction channel. The results show that this analysis protocol not only assigns all trajectories into different photoisomerization reaction channels but also extracts the major molecular motion without the requirement of the pre-known knowledge of the active photoisomerization site. As a side product of this analysis tool, it is also easy to find the so-called "typical" or "representative" trajectory for each reaction channel.


Assuntos
Biliverdina/análogos & derivados , Simulação de Dinâmica Molecular , Algoritmos , Biliverdina/química , Biliverdina/efeitos da radiação , Análise por Conglomerados , Isomerismo , Processos Fotoquímicos
17.
Soft Matter ; 13(43): 7962-7968, 2017 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-29043365

RESUMO

By probing the electric potential at the hexadecane-water interface with second harmonic generation and the zeta potential at the surface of a hexadecane droplet in its emulsion, we show that hydronium ions don't have a specific affinity to the oil-water interface although hydroxide ions do. The observed apparent affinity of the hydronium ions to the hexadecane-water interface is more likely a result of the electro-static attraction effect. The adsorption free energy of the hydroxide ions at the oil-water interface was estimated to be -8.3 kcal mol-1. This study provides more experimental evidence for understanding the behavior of hydronium and hydoxide ions at the oil-water interface.

18.
J Chem Theory Comput ; 13(10): 4611-4623, 2017 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-28862858

RESUMO

On-the-fly trajectory-based nonadiabatic dynamics simulation has become an important approach to study ultrafast photochemical and photophysical processes in recent years. Because a large number of trajectories are generated from the dynamics simulation of polyatomic molecular systems with many degrees of freedom, the analysis of simulation results often suffers from the large amount of high-dimensional data. It is very challenging but meaningful to find dominating active coordinates from very complicated molecular motions. Dimensionality reduction techniques provide ideal tools to realize this purpose. We apply two dimensionality reduction approaches (classical multidimensional scaling and isometric feature mapping) to analyze the results of the on-the-fly surface-hopping nonadiabatic dynamics simulation. Two representative model systems, CH2NH2+ and the phytochromobilin chromophore model, are chosen to examine the performance of these dimensionality reduction approaches. The results show that these approaches are very promising, because they can extract the major molecular motion from complicated time-dependent molecular evolution without preknown knowledge.

19.
Phys Chem Chem Phys ; 19(29): 19168-19177, 2017 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-28702524

RESUMO

The nonadiabatic dynamics of keto isocytosine in the gas phase has been investigated using the on-the-fly trajectory surface hopping method based on two electronic-structure methods: SA-CASSCF and ADC(2). The results estimate an excited-state lifetime of around 1000 fs at the SA-CASSCF level, while a much shorter lifetime of 250-350 fs is obtained at the ADC(2) level. Although three conical intersections (CIs) (Ethyl. I, Ethyl. II and C[double bond, length as m-dash]O stretching) are relevant to the nonadiabatic decay of keto isocytosine, their contributions to the nonadiabatic decay are highly dependent on the electronic-structure methods employed in the dynamics simulation. The Ethyl. II CI is the main channel in the dynamics simulations at the SA-CASSCF level, while the C[double bond, length as m-dash]O stretching CI becomes dominant at the ADC(2) levels. Other high-level electronic-structure methods (MR-CISD and MS-CASPT2) are involved to benchmark our dynamics results. Through the analysis of the reaction pathways from the ground state minimum to the relevant CIs, we expect that the excited-state dynamical features obtained at the MR-CISD and MS-CASPT2 levels should be very similar to those at the SA-CASSCF level. The comparison of results obtained using different excited-state electronic-structure methods could provide guidance for further studies of similar systems.

20.
J Phys Chem A ; 121(6): 1240-1249, 2017 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-28103031

RESUMO

Photoisomerization dynamics of a light-driven molecular rotary motor, 9-(2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene, is investigated with trajectory surface-hopping dynamics at the semiempirical OM2/MRCI level. The rapid population decay of the S1 excited state for the M isomer is observed, with two different decay time scales (500 fs and 1.0 ps). By weighting the contributions of fast and slow decay trajectories, the averaged lifetime of the S1 excited state is about 710 fs. The calculated quantum yield of the M-to-P photoisomerization of this molecular rotary motor is about 59.9%. After the S0 → S1 excitation, the dynamical process of electronic decay is followed by twisting about the central C═C double bond and the motion of pyramidalization at the carbon atom of the stator-axle linkage. Although two S0/S1 minimum-energy conical intersections are obtained at the OM2/MRCI level, only one conical intersection is found to be responsible for the nonadiabatic dynamics. The existence of "dark state" in the molecular rotary motor is confirmed through the simulated time-resolved fluorescence emission spectrum. Both quenching and red shift of fluorescence emission spectrum observed by Conyard et al. [ Conyard, J.; Addison, K.; Heisler, I. A.; Cnossen, A.; Browne, W. R.; Feringa, B. L.; Meech, S. R. Nat. Chem. 2012 , 4 , 547 - 551 ; Conyard, J.; Conssen, A.; Browne, W. R.; Feringa, B. L.; Meech, S. R. J. Am. Chem. Soc. 2014 , 136 , 9692 - 9700 ] are well understood. We find that this "dark state" in the molecular rotary motor is not a new electronic state, but the "dark region" with low oscillator strength on the initial S1 state.

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