3发色团激发态分子内质子转移机理的研究

采用密度泛函(DFT)和含时密度泛函理论(TDDFT)方法对一种新合成的发色团(3)在非质子性溶剂DMSO中的激发态分子内质子转移机制进行了理论研究.基于3发色团的基态和激发态优化结构,计算得到了该发色团中与氢键相关的键长和键角的大小,以及与氢键相连接的O-H键红外振动光谱,发现分子内氢键在激发态下有增强的趋势.理论计算得到的吸收谱和荧光谱的峰值与实验测得的结果吻合得很好,证明了所采用的理论方法的正确性与合理性.最终,通过对该发色团的分子内电荷转移与电荷分布的分析,证实了激发态分子内质子转移发生的可能性,并说明了其转移过程的发生机制.     

10-羟基苯并喹啉激发态分子内质子转移取代基效应的理论研究

运用密度泛函(DFT)和含时密度泛函(TDDFT)计算方法研究了10-羟基苯并喹啉(HBQ)及其衍生物分子内质子转移过程,探究了取代基效应对质子转移过程的影响,研究发现,HBQ及其衍生物可以形成分子内氢键,且激发态时氢键增强.基态时各分子以醇式构型稳定存在,激发态时酮式构型为优势构象.各化合物的最大吸收峰和发射峰主要是电子从HOMO到LUMO之间的跃迁引起的.基态分子内质子转移(醇式→酮式)需要跃过较高的能垒因而难以发生,而激发态时只需跃过较低能垒就很容易发生分子内质子转移,吸电子基的引入可以使该过程的能垒降低,因此吸电子基有利于激发态质子转移.取代基效应影响化合物的光谱性质.     

取代基对2-(2-羟基苯基)苯并噻唑分子内氢键及质子转移的影响:密度泛函理论研究

运用密度泛函(DFT)和含时密度泛函(TD DFT)理论方法研究了在2-(2-羟基苯基)苯并噻唑(HBT)苯环羟基的邻位或对位分别引入羟基和醛基后的衍生物分子内质子转移过程,考察了取代基的电子效应及取代位置对分子内氢键和质子转移反应的影响,模拟计算了各分子的IR振动光谱和电子光谱.研究发现,HBT及其衍生物分子可以形成分子内氢键,且激发态时氢键增强.基态时以醇式构型稳定存在,激发态时酮式结构为优势构象.分子的最大吸收峰和发射峰主要源于电子从前线分子轨道HOMO到LUMO之间的跃迁.基态分子内质子转移需要越过较高的能垒因而难以发生,而激发态时只需越过较低能垒就很容易发生激发态分子内质子转移.取代基的电子效应和取代位置对HBT分子氢键强度、互变异构体的相对稳定性、电子光谱及质子转移反应的能垒均有一定影响.     

取代基对2-(2-羟基苯基)苯并噻唑分子内氢键及质子转移的影响:密度泛函理论研究

运用密度泛函(DFT)和含时密度泛函(TD DFT)理论方法研究了在2-(2-羟基苯基)苯并噻唑(HBT)苯环羟基的邻位或对位分别引入羟基和醛基后的衍生物分子内质子转移过程，考察了取代基的电子效应及取代位置对分子内氢键和质子转移反应的影响，模拟计算了各分子的IR振动光谱和电子光谱.研究发现，HBT及其衍生物分子可以形成分子内氢键，且激发态时氢键增强.基态时以醇式构型稳定存在，激发态时酮式结构为优势构象.分子的最大吸收峰和发射峰主要源于电子从前线分子轨道HOMO到LUMO之间的跃迁.基态分子内质子转移需要越过较高的能垒因而难以发生，而激发态时只需越过较低能垒就很容易发生激发态分子内质子转移.取代基的电子效应和取代位置对HBT分子氢键强度、互变异构体的相对稳定性、电子光谱及质子转移反应的能垒均有一定影响.     

激发态下甘氨酸与水分子间氢键性质研究

在生物体中氨基酸通常以水作为溶剂,是形成细胞的重要成分.在该环境下,分子间氢键的产生会对氨基酸分子与水分子的结构和性质产生影响.为了研究其在基态和激发态下的性质,本文利用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对甘氨酸分子和H₂O分子在基态和激发态下的分子间氢键的静电势、键长、自然键轨道(NBO)电荷、分子中的原子理论(AIM)分析、Wiberg键级b、红外(IR)光谱、空穴-电子轨道和基态与激发态之间的电子转移进行了理论研究.结果表明：分子间氢键的形成会导致分子结构的改变和红外光谱振动频率的移动.在激发态下,分子间氢键有不同程度的增强或减弱.该计算结果为氢键的形成和激发态下分子间氢键的研究提供理论依据.     

溶剂极性对1，5-二羟基蒽醌分子双质子转移过程的影响

具有激发态分子内双质子转移特性的分子在荧光传感器、激光材料、生物分子探针等领域具有广泛的应用. 羟基蒽醌作为蒽醌类化合物是自然界中广泛存在且具有质子转移特性的次级代谢物,其衍生物已被广泛研究并成功应用于染料、免疫增强和抗癌药物. 近年来,1,5-二羟基蒽醌(1,5-DHAQ)作为一种具有两个分子内氢键的羟基蒽醌衍生物受到了广泛的关注. 本文采用飞秒瞬态吸收光谱结合含时密度泛函理论方法研究了溶剂极性对1,5-DHAQ分子激发态分子内双质子转移过程的影响. 1,5-DHAQ分子在甲苯、四氢呋喃和乙腈溶剂中的稳态荧光光谱表明,溶剂极性的改变对1,5-DHAQ的荧光峰位置产生了影响. 瞬态吸收光谱表明,溶剂极性的增大加快了质子转移的速率. 超快动力学拟合结果表明,溶剂极性的增大有助于加快1,5-DHAQ分子中的激发态分子内双质子转移过程. 此外,通过理论计算得到的势能曲线分析表明质子转移的能垒随着溶剂极性的增加而逐渐减小,从而促进1,5-DHAQ分子激发态分子内双质子转移过程的发生,这进一步验证和解释了实验结果. 本工作有助于开发和合成更稳定、高效的羟基蒽醌衍生物.     

通过改变原子电负性调控异硫氰酸苯并恶唑荧光染料的激发态分子内质子转移过程和光物理性质

激发态分子内质子转移因其独特的光学性质而受到研究人员的青睐. 然而,关于改变原子电负性对激发态分子内质子转移过程和光物理性质影响的系统研究相对较少. 本文通过理论方法选择了一系列苯并噁唑异硫氰酸酯荧光染料(2-HOB、2-HSB 和2-HSeB),并通过改变氧族原子的电负性,系统地研究了激发态分子内质子转移过程和光物理性质. 计算的键角、键长、能隙和红外光谱分析表明,3个分子的分子内氢键强度依次为2-HOB<2-HSB<2-HSeB. 相应地,势能曲线的能垒大小为2-HOB>2-HSB>2-HSeB. 此外,计算的电子光谱表明,随着原子电负性的降低,发射光谱发生红移. 本工作将为基于激发态分子内质子转移性质的新型染料的合成和应用提供一定的理论指导.     

芳香性取代基对2-(2-羟基苯基)苯并咪唑激发态质子转移和光谱性质影响的理论研究

运用密度泛函(DFT)和含时密度泛函(TD DFT)理论方法研究了在2-(2-羟基苯基)苯并咪唑(HBI)苯环羟基的对位分别被呋喃基、吡咯基等五种芳香性取代基后的衍生物(HBI-R)分子内质子转移过程,考察了取代基的电子离域效应对分子结构、分子内氢键和质子转移的影响,模拟计算了各分子的IR振动光谱和电子光谱。研究发现,基态的HBI与HBI-R分子内氢键O—H…N比O…H—N强度大,因氢键中的O—H增长和H—N的缩短,激发态氢键O—H…N弱于O…H—N强度,基态和激发态的稳定构型分别为醇式和酮式结构,取代基总体上使酮式构型相对稳定性有所增加,但呋喃基、吡咯基和噻吩基却略降低了激发态酮式构型相对稳定性。取代基降低了HBI基态和激发态分子内质子转移反应的能垒,但影响不大。电子吸收光谱的最大吸收峰和荧光光谱的最大发射峰主要源于前线分子轨道HOMO与LUMO之间的电子跃迁,芳环取代基增强了电子离域效应,使光谱的吸收峰和发射峰波长均有较大的红移。     

电子激发和溶剂效应对芴酮-甲醇分子间氢键增强现象的理论研究 (cited: 1)

理论研究了电子激发和溶剂效应导致的芴酮-甲醇复合体系中分子间氢键增强现象．通过基态和激发态性质的计算,不仅展示了分子间氢键键长的变化以及变化在振动光谱中的影响,而且揭示了导致氢键变化的内在物理机制：溶质分子的电子激发及溶剂化效应引起的电子重新分布,增大了溶质和溶剂分子的偶极矩,导致了它们之间的相互作用的增大,并最终加强了分子间氢键的强度．还分别对处于液相及气相中的复合体的基态和激发态的几何结构、红外谱、复合体及构成分子的偶极矩进行了理论计算,结果阐明了电子激发与溶剂化效应对氢键变化的贡献,同时还发现只有进一步引入溶剂化效应,复合体的基态、激发态的性质才能与实验达到精确一致．所有激发态均采用所开发的基于含时密度泛函理论解析计算一阶、二阶激发态能量导数的方法．     

团簇LaO的理论研究

采用密度泛函理论研究LaO团簇体系。中性分子LaO的基态是两重态(2Σ),阴离子LaO-和阳离子LaO 的基态都是单重态(1Σ)。使用不同的方法计算团簇LaO的电子亲和能和电离能。计算结果表明用BLYP方法和弥散极化基组计算结果和实验数据吻合较好。用含时密度泛函理论计算团簇LaO的低能激发态,从理论上归属LaO-的光电子能谱的谱峰和LaO的吸收光谱的谱峰。计算得到与实验一致的结果。     

Theoretical investigation on the excited‐state intramolecular proton transfer mechanism of 2‐(2′‐benzofuryl)‐3‐hydroxychromone

Spectroscopic studies on excited‐state proton transfer of a new chromophore 2‐(2′‐benzofuryl)‐3‐hydroxychromone (BFHC) have been reported recently. In the present work, based on the time‐dependent density functional theory (TD‐DFT), the excited‐state intramolecular proton transfer (ESIPT) of BFHC is investigated theoretically. The calculated primary bond lengths and 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 (IR) vibrational spectra as well as the calculated hydrogen bonding energies. Further, hydrogen bonding strengthening manifests the tendency of excited state proton transfer. Our calculated results reproduced absorbance and fluorescence emission spectra of experiment, which verifies that the TD‐DFT theory we used is reasonable and effective. The calculated Frontier Molecular Orbitals (MOs) 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 14.5 kcal/mol is discovered in the S₀ state. However, a lower potential energy barrier of 5.4 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.     

Excited state intramolecular proton transfer mechanism of o-hydroxynaphthyl phenanthroimidazole

By utilizing the density functional theory(DFT) and the time-dependent density functional theory(TDDFT), the excited state intramolecular proton transfer(ESIPT) mechanism of o-hydroxynaphthyl phenanthroimidazole(HNPI) is studied in detail. Upon photo is excited, the intramolecular hydrogen bond is obviously enhanced in the S_1 state, which thus promotes the ESIPT process. Hydrogen bond is shown to be strengthened via comparing the molecular structures and the infrared vibration spectra of the S_0 and S_1 states. Through analyzing the frontier molecular orbitals, we can conclude that the excitation is a type of the intramolecular charge transfer excitation, which also indicates the trend of proton transfer in S_1 state. The vertical excitation based on TDDFT calculation can effectively repeat the absorption and fluorescence spectra of the experiment. However, the fluorescence spectrum of normal structure, which is similar to the spectrum of isomer structure is not detected in the experiment. It can be concluded that the fluorescence measured in the experiment is attributed to both structures. In addition, by analyzing the potential energy curves(PECs) calculated by the B3 LYP functional method, it can be derived that since the molecule to cross the potential barrier in the S_1 state is smaller than in the S_0 state and the reverse proton transfer process in the S_1 state is more difficult than in the S_0 state, the ESIPT occurs in the S_1 state.     

Ab initio investigation of excited state dual hydrogen bonding interactions and proton transfer mechanism for novel oxazoline compound

Owing to the importance of excited state dynamical relaxation, the excited state intramolecular proton transfer(ESIPT) mechanism for a novel compound containing dual hydrogen bond(abbreviated as "1-enol") is studied in this work.Using density functional theory(DFT) and time-dependent density functional theory(TDDFT) method, the experimental electronic spectra can be reproduced for 1-enol compound. We first verify the formation of dual intramolecular hydrogen bonds, and then confirm that the dual hydrogen bond should be strengthened in the first excited state. The photo-excitation process is analyzed by using frontier molecular orbital(HOMO and LUMO) for 1-enol compound. The obvious intramolecular charge transfer(ICT) provides the driving force to effectively facilitate the ESIPT process in the S1 state. Exploration of the constructed S0-state and S1-state potential energy surface(PES) reveals that only the excited state intramolecular single proton transfer occurs for 1-enol system, which makes up for the deficiencies in previous experiment.     

The ESIPT mechanism of dibenzimidazolo diimine sensor: a detailed TDDFT study

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.     

Theoretical insight into the excited‐state behavior of a novel Compound 1: A TDDFT investigation

In the present work, using density functional theory and time‐dependent density functional theory methods, we investigated and presented the excited‐state intramolecular proton transfer (ESIPT) mechanisms of a novel Compound 1 theoretically. Analyses of electrostatic potential surfaces and reduced density gradient (RDG) versus sign(λ₂)ρ, we confirm the existence of intramolecular hydrogen bond O1‐H2···N3 for Compound 1 in the S₀ state. Comparing the primary structural variations of Compound 1 involved in the intramolecular hydrogen bond, we find that O1‐H2···N3 should be strengthened in the S₁ state, which may facilitate the ESIPT process. Concomitantly, infrared (IR) vibrational spectra analyses further verify the stability of hydrogen bond. In addition, the role of charge transfer interaction has been addressed under the frontier molecular orbitals, which depicts the nature of electronical excited state and supports the ESIPT reaction. The theoretically scanned and optimized potential energy curves according to variational O1‐H2 coordinate demonstrate that the proton transfer process should occur spontaneously in the S₁ state. It further explains why the emission peak of Compound 1‐enol was not reported in previous experiment. This work not only presents the ESIPT mechanism of Compound 1 but also promotes the understanding of this kind of molecules for further applications in future.     

Time-dependent density functional theory study on excited state intramolecular proton transfer of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

The time-dependent density functional theory (TDDFT) method was carried out to investigate the excited state intramolecular proton transfer (ESIPT) process of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a). 1a has two tautomeric forms: one is 1a(O), which is induced by intramolecular hydrogen bond O-H?O=C, and the other one is 1a(N), which is caused by intramolecular hydrogen bond O-H?N. From excited state to tautomer excited state coming from ESIPT, the hydroxyl hydrogen breaks away and the dissociated hydrogen adsorbed on pyridinic nitrogen or carbonyl oxygen formed new intramolecular HB and the corresponding bond length and bond angle varied greatly. In comparison, a similar process of proton transfer for 1a(N)H⁺ protonated 1a(N) from ground state to excited state was obtained. This detailed proton transfer mechanism was provided by molecular orbitals analysis and it may be applied to molecular switch and organic Lewis acid/base. We investigated the excited state proton transfer mechanism of the four molecules through the theoretical method for the first time and gave unambiguous geometry of excited state.     

A TDDFT study on the hydrogen-bonding effect on ESIPT mechanism for [2,2′-bipyridyl]-3,3′-diol-(H2O) n (n = 0, 1, 2) clusters: single or double?

The excited-state intramolecular proton transfer (ESIPT) mechanisms of [2,2′-bipyridyl]-3,3′-diol (BP(OH)₂) in gas are studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The intramolecular hydrogen bond (H-bond) is strengthened in the first excited-state in view of the structural parameters and infrared (IR) vibrational frequencies. The enhanced intramolecular H-bond is favourable for ESIPT process. The effect of the extra intermolecular H-bond between BP(OH)₂ and water on ESIPT is considered. The potential energy surfaces, molecular electrostatic potential, topological analysis, frontier molecular orbitals, absorption and fluorescence spectra are investigated. Our calculated results show that the intermolecular H-bond enhances the intramolecular H-bond, changes the mechanism and decreases the barrier height of ESIPT process.     

A theoretical study on the ESPT mechanism for a novel Bis‐HPBT fluorophore

In this work, based on the density functional theory and time‐dependent density functional theory methods, the properties of the 2 intramolecular hydrogen bonds (O1‐H2···N3 and O4‐H5···N6) of a new photochemical sensor 4‐(3‐(benzo[d]thiazol‐2‐yl)‐5‐tert‐butyl‐4‐hydroxybenzyl)‐2‐(benzo[d]thiazol‐2‐yl)‐6‐tert‐butyl phenol (Bis‐HPBT) have been investigated in detail. The calculated dominating bond lengths and bond angles about these 2 hydrogen bonds (O1‐H2···N3 and O4‐H5···N6) demonstrate that the intramolecular hydrogen bonds should be strengthened in the S₁ state. In addition, the variations of hydrogen bonds of Bis‐HPBT have been also testified based on infrared vibrational spectra. Our theoretical results reproduced absorption and emission spectra of the experiment, which verifies that the theoretical level we used is reasonable and effective in this work. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer (ESIPT) process. Frontier molecular orbitals depict the nature of electronically excited state and support the ESIPT reaction. According to the calculated results of potential energy curves along stepwise and synergetic O1‐H2 and O4‐H5 coordinates, the potential energy barrier of approximately 1.399 kcal/mol is discovered in the S₁ state, which supports the single ESIPT process along with 1 hydrogen bond of Bis‐HPBT. In other words, the proton transfer reaction can be facilitated based on the electronic excitation effectively. In turn, through the process of radiative transition, the proton‐transfer Bis‐HPBT‐SPT form regresses to the ground state with the fluorescence of 539 nm.