2-(2′-氨基苯基)苯并咪唑衍生物分子内质子转移理论研究:取代基效应

研究了2-(2′-氨基苯基)苯并咪唑(APBI)氨基中一个H被CH3(E-C),SiH3(E-OSi),NH2(E-N),COH(E-CO),NO2(E-NO2),CF3(E-F),CN(E-CN3),OMe(E-OMe),COCH3(E-CC),Ts(E-S),p-CH3C6H4CO(E-C=O)和p-CH3C6H4NHCO(E-NH)取代后,其基态及激发态分子内质子转移(ESIPT)性质的变化规律.结果表明各衍生物基态最稳定构型为烯醇式构型E,次稳定构型旋转异构体R,酮式构型K只有当取代基为E-CN3,E-F,E-NO2,E-N,E-OMe和E-S时才存在.基态各环的核独立化学位移(NICS)研究表明取代基的引入会影响APBI环电子离域性.所有APBI衍生物都能发生激发态分子内质子转移,当引入取代基为E-CN3,E-N或E-OMe时,所得的APBI衍生物S1态分子内质子转移是无能垒过程;引入取代基为E-C,E-C=O或E-OSi时,对APBI的ESIPT势能面基本无影响,而当取代基为E-CC,E-NH,E-CO,E-F,E-NO2和E-S时,使得S1态APBI的K*构型能量低于E*.     

2-(2-巯苯基)苯并噁唑分子内质子转移取代基电子效应的密度泛函理论研究

在B3LYP/6-31G(d,p)和TDB3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上研究了2-(2-巯苯基)苯并噁唑及其衍生物基态和激发态分子内质子转移现象,并探讨取代基电子效应对分子内质子转移的影响,研究结果表明,在基态时,硫醇式异构体为优势构象,供电子取代基使基态分子内正向质子转移能垒(烯醇式→酮式)升高;而吸电子取代基则可降低能垒,有利于基态分子内质子转移并有助于硫酮式异构体的稳定.在激发态时,硫酮式结构为优势构象,所研究的2-(2-巯苯基)苯并噁唑化合物及衍生物均可以发生无能垒或低能垒(≤1.5kJ/mol)的激发态分子内质子转移.巯苯基部分是激发态失活的主要活性部分,供电子基团有利于激发态的质子转移,吸电子基团使激发态跃迁困难,不利于激发态的质子转移.     

基于异噁唑酮类份菁染料的激发态分子内质子转移的研究

运用量子化学理论计算方法研究了3-甲基-4-(1H-吲哚-3-次甲基)-异噁唑-5-酮(A)及其衍生物份菁染料的激发态分子内质子转移性质.研究表明:在基态3种染料AH(R=H),AO(R=—O(H3))和AP(R=—O(H2Ph))只存在酮式构型,在激发态AH与AP存在酮式和烯醇式2种构型,而AO存在酮式、烯醇式和仲胺式3种构型.红外光谱表明化合物从基态跃迁到激发态存在分子内的氢键增强作用,势能曲线显示激发态的质子转移为放热反应且能垒较低,通过分析电子光谱得到具有较大斯托克位移的激发态分子内质子转移的荧光发射峰,前线分子轨道理论计算进一步说明了其质子转移的发生过程.     

2-(3-巯基-2-吡啶基)苯并咪唑分子内质子转移及溶剂化效应

在B3LYP/6-31G(d,p)和TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上,研究了2-(3-巯基-2-吡啶基)苯并咪唑(MPyBI)在气相和七种溶剂(环己烷、苯、三氯甲烷、乙醇、乙腈、二甲亚砜和水)中基态和激发态的分子内质子转移(GSIPT和ESIPT)过程.在基态势能面的研究中发现,该化合物存在分子内双质子转移,其中分步的双质子转移在动力学上具有优势.同时对激发态质子转移势能面及激发态转移过程中的光物理现象进行了研究,结果表明该化合物存在快速的无能垒的激发态分子内质子转移,随着溶剂极性的增强,可以降低基态过渡态的能垒,改变硫醇式与硫酮式互变异构体的比例,从而灵敏地控制荧光的强度.     

Theoretical Study on Excited-State Intramolecular Proton Transfer of 2-（2＇-Aminophenyl）benzimidazole Derivatives： Substituent EffectE-C=O or E-OSi. The K＊ configuration become more stable than E＊ in S~ state when substitutent is E-CC, E-NH, E-CO, E-...

研究了2-（2’-氨基苯基）苯并咪唑（APBI）氨基中一个H被CH3（E-C）,Sill3（E-OSi）,NH2（E-N）,COH（E-CO）,N02（E-N02）,CF3（E-F）,CN（E-CN3）,OMe（E-OMe）,COCH3（E-CC）,Ts（E-S）,P-CH3C6H4CO（E-C=0）和P-CH3C6H4NHCO（E-NH）取代后,其基态及激发态分子内质子转移（ESIPT）性质的变化规律．结果表明各衍生物基态最稳定构型为烯醇式构型E,次稳定构型旋转异构体R,酮式构型K只有当取代基为E-CN3,E-F,E-N02,E-N,E-OMe和E-S时才存在．基态各环的核独立化学位移（NICS）研究表明取代基的引入会影响APBI环电子离域性．所有APBI衍生物都能发生激发态分子内质子转移,当引入取代基为E-CN3,E-N或E-OMe时,所得的APBI衍生物S1态分子内质子转移是无能垒过程;引入取代基为E．c,E．C=O或E．OSi时,对APBI的ESIPT势能面基本无影响,而当取代基为E-CC,E-NH,E-CO,E-F,E-N02和E-S时,使得Sl态APBI的K’构型能量低于E     

硝基烃光异构化反应的密度泛函理论计算

采用DFT(B3LYP)计算方法, 在6-31G*水平上获得了反式-β-硝基苯乙烯、硝基乙烯和硝基甲烷基态异构化反应时的过渡态分子结构, 并计算了异构化能垒及激发态电子跃迁能. 结果显示, 反式-β-硝基苯乙烯和硝基苯与硝基甲烷相比具有较短的过渡态C—N键长, 较低的异构化能垒, 并且随着不饱和度的增加, 硝基苯和反式-β-硝基苯乙烯电子垂直跃迁能与基态异构化反应过渡态之间能量的差值ΔE迅速减小. 从能量的角度分析, 取代基的不饱和度越大, 越有利于激发态势能面与异构化反应势能面发生锥型或漏斗交叉, 因而越有利于光化学反应沿光异构化通道进行. 激发态分子的初始电子运动的定域或离域特征的差别可能是导致硝基苯等硝基芳烃与硝基甲烷等硝基烷烃光解通道不同的一个重要原因.     

基于2-(2'-羟基苯基)苯并噻唑的激发态分子内质子转移化合物的光物理行为研究

运用量子化学理论计算方法结合现代光谱技术对激发态分子内质子转移(Excited state intramolecular proton transfer,ESIPT)化合物DHBIA{N,N'-di[3-hydroxy-4-(2'-benzothiazole)phenyl]5-tert-butyl-isophthalic amide}的激发态光物理行为进行了深入研究.研究表明:该化合物的醇式激发态很容易发生分子内C—N单键的快速扭转,使分子构型发生大幅扭曲,并显现出明显的扭曲的分子内电荷转移(Twisted intramolecular charge transfer,TICT)特征,激发态的这种构型弛豫导致的非辐射失活与质子转移过程相竞争,导致了激发态质子转移效率的降低以及相应酮式结构发光物种的大幅减少,从而致使化合物稀溶液的发光极为微弱.这种TICT特征也正是导致该化合物具有聚集发光增强性质的重要原因之一.     

含不同质子供体的2-苯基苯并三唑衍生物激发态质子转移的理论研究

用密度泛函理论(DFT)和二级微扰理论(MP2)研究了带不同质子供体的2-苯基苯并三唑衍生物: 2-(2-羟苯基)苯并三唑(H-TIN), 2-(2-氨苯基)苯并三唑(APyBT)和2-(2-巯苯基)苯并三唑(MPyBT)的激发态分子内质子转移(ESIPT)性质以及它们作为紫外光吸收剂的光物理机制. 结果表明, 在基态时三个化合物的最稳定异构体是均存在分子内氢键的正常构型N, 而互变异构体T和其扭曲构型T_twisted都是不稳定的. 激发态势能曲线表明H-TIN和APyBT的ESIPT分别需要克服约7.06和20.7 kJ/mol的能垒, 而MPyBT的ESIPT无需能垒|同时结合分子轨道, 电荷差分密度三维立体图的分析结果表明三个化合物都能发生ESIPT, 并且伴随有扭曲分子内电荷转移, 这些原因均表明它们都具有好的紫外光稳定作用.     

3-羟基邻苯二甲酰亚胺全水溶性次氯酸荧光探针及其应用

利用二甲基硫代氨基甲酸酯对次氯酸(HOCl)的特异性和吡啶盐的水溶性,以4-羟基异苯并呋喃-1,3-二酮作为原料,设计合成了一种检测HOCl的全水溶性激发态分子内质子转移(ESIPT)荧光探针.由于二甲氨基硫代甲酸酯对羟基的保护,探针分子内的ESIPT作用被阻碍,自身无荧光;当加入HOCl时,HOCl氧化二甲氨基硫代甲...     

基于ESIPT机理的近红外硫醇探针及其生物成像研究

本文利用激发态分子内质子转移(ESIPT)过程可产生长波长酮式发射的特点,以HBT(2-(2’-羟基苯基)苯并噻唑)为骨架,2,4-二硝基苯磺酸基作为硫醇位点掩盖酚羟基,与丙二腈缩异佛尔酮通过共轭双键相连,构建了近红外硫醇探针SYN.该探针实现了近红外区对硫醇的定量检测,并在细胞水平上对硫醇进行了成像研究.     

Enol-keto tautomerism of aromatic photochromic Schiff base N,N'-bis(salicylidene)-p-phenylenediamine: ground state equilibrium and excited state deactivation studied by solvatochromic measurements on ultrafast time scale

A photochromic symmetric Schiff base, N,N'-bis(salicylidene)-p-phenylenediamine, is proposed as a probe for the study of solvent dependent enol-keto tautomerism in the ground and excited states. The ground state equilibrium between the enol-keto tautomers is found to depend mainly not on polarity but on the proton donating ability of the solvent. Upon selective excitation of each of these tautomers, the same excited state of a keto tautomer is created: in enol, after the ultrafast excited state intramolecular proton transfer (ESIPT), reaction, and in keto tautomer, directly. Then some part (<30%) of excited molecules are transferred to the photochromic form in its ground state. The evidence of another ultrafast deactivation channel in the excited enol tautomer competing with ESIPT has been found. The solvent does not influence the ESIPT dynamics nor the efficiency of the creation of the photochrome.     

Ultrafast branching of reaction pathways in 2-(2'-hydroxyphenyl)benzothiazole in polar acetonitrile solution

In a combined study on the photophysics of 2-(2'-hydroxyphenyl)-benzothiazole (HBT) in polar acetonitrile utilizing ultrafast infrared spectroscopy and quantum chemical calculations, we show that a branching of reaction pathways occurs on femtosecond time scales. Apart from the excited-state intramolecular hydrogen transfer (ESIHT) converting electronically excited enol tautomer into the keto tautomer, known to be the dominating mechanism of HBT in nonpolar solvents such as cyclohexane and tetrachloroethene, in acetonitrile solution twisting also occurs around the central C-C bond connecting the hydroxyphenyl and benzothiazole units in both electronically excited enol and keto tautomers. The solvent-induced intramolecular twisting enables efficient internal conversion pathways to both enol and keto tautomers in the electronic ground state. Whereas relaxation to the most stable enol tautomer with twisting angle Θ = 0° implies full ground state recovery, a small fraction of HBT molecules persists as the keto twisting conformer with the twisting angle Θ = 180° for delay times extending beyond 120 ps.     

Femtosecond dynamics on 2-(2'-hydroxy-4'-diethylaminophenyl)benzothiazole: solvent polarity in the excited-state proton transfer.

Detailed insights into the excited-state enol(N*)-keto(T*) intramolecular proton transfer (ESIPT) reaction in 2-(2'-hydroxy-4'-diethylaminophenyl)benzothiazole (HABT) have been investigated via steady-state and femtosecond fluorescence upconversion approaches. In cyclohexane, in contrast to the ultrafast rate of ESIPT for the parent 2-(2'-hydroxyphenyl)benzothiazole (>2.9+/-0.3 x 10(13) s(-1)), HABT undergoes a relatively slow rate (approximately 5.4+/-0.5 x 10(11) s(-1)) of ESIPT. In polar aprotic solvents competitive rate of proton transfer and rate of solvent relaxation were resolved in the early dynamics. After reaching the solvation equilibrium in the normal excited state (N(eq)*), ESIPT takes place with an appreciable barrier. The results also show N(eq)*(enol)<-->T(eq)*(keto) equilibrium, which shifts toward N(eq)* as the solvent polarity increases. Temperature-dependent relaxation dynamics further resolved a solvent-induced barrier of 2.12 kcal mol(-1) for the forward reaction in CH(2)Cl(2). The observed spectroscopy and dynamics are rationalized by a significant difference in dipole moment between N(eq)* and T(eq)*, while the dipolar vector for the enol form in the ground state (N) is in between that of N(eq)* and T(eq)*. Upon N-->N* Franck-Condon excitation, ESIPT is energetically favorable, and its rate is competitive with the solvation relaxation process. Upon reaching equilibrium configurations N(eq)* and T(eq)*, forward and/or backward ESIPT takes place with an appreciable solvent polarity induced barrier due to differences in polarization equilibrium between N(eq)* and T(eq)*.     

Restriction of Photoinduced Twisted Intramolecular Charge Transfer

An intensive investigation of structure–property relationships in the aggregation‐induced enhanced emission (AIEE) of luminescent compounds is essential for the rational design of highly emissive solid‐state materials. In the AIEE‐active compounds N,N′‐bis[3‐hydroxy‐4‐(2′‐benzothiazolyl)phenyl]isophthalamide and N,N′‐bis[3‐hydroxy‐4‐(2′‐benzothiazolyl)phenyl]‐5‐tert‐butylisophthalamide, fast photoinduced twisted intramolecular charge transfer (TICT) of the enol excited state is found to be mainly responsible for the weak emission of their dilute solutions. The photoinduced TICT enol excited state is formed with a greatly distorted configuration, due to the large rotation about the C? N single bond. This facilitates nonradiative TICT decay from the normal enol excited state to the highly twisted enol excited state, rather than proton‐transfer decay to the keto excited state. In aggregates, photoinduced nonradiative deactivation of TICT is strongly prohibited, so that excited‐state intramolecular proton transfer (ESIPT) becomes the dominant decay, and hence contributes greatly to the subsequent emission enhancement of the keto form. Molecular design and investigation of analogous single‐armed compounds further verifies this kind of AIEE mechanism.     

Excited state intramolecular proton transfer in 5-hydroxy flavone: A DFT study

Potential energy surfaces (PES) for the ground and excited state intramolecular proton transfer (ESIPT) processes in 5-hydroxy-flavone (5HF) were studied using DFT-B3LYP/6-31G(d) and TD-DFT/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer (GSIPT) in 5HF. Excited states PES calculations support the existence of ESIPT process in 5HF. ESIPT in 5HF has been explained in terms of HOMO, LUMO electron density of the enol and keto tautomer of 5HF. PES scan by phenyl group rotation suggests that the twisted form, i.e., phenyl group rotated by 18.7° out of benzo-γ-pyrone ring plane is the most stable conformer of 5HF.     

DFT based computational study on the excited state intramolecular proton transfer processes in o-hydroxybenzaldehyde

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of o-hydroxybenzaldehyde (OHBA) were studied using DFT-B3LYP/6-31G(d) and TD-DFT-B3LYP/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in this compound. Excited states PE calculations support the ESIPT process in OHBA. The contour PE diagram and the variation of oscillator strength along the proton transfer co-ordinate support the dual emission in OHBA. Our calculations also support the experimental observations of Nagaoka et al. [S. Nagaoka, U. Nagashima, N. Ohta, M. Fujita, T. Takemura, J. Phys. Chem. 92 (1988) 166], i.e. normal emission of the title compound comes from S(2) state and the red-shifted proton transfer band appears from the S(1) state. ESIPT process has also been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of OHBA and from the potential energy surfaces.     

气相水杨酸激发态分子内质子转移特性分析

采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)研究了气相水杨酸(SA)分子的激发态氢键动力学过程。通过对水杨酸分子基态和激发态结构的优化,以及对其稳态吸收和发射光谱特性、前线分子轨道、红外振动光谱和势能曲线的计算分析,阐明水杨酸分子内质子转移可在激发态下自发地发生,导致其激发态可存在烯醇式和酮式两种异构体结构,并揭示了这种质子转移源于分子内电荷转移的激发态氢键的加强机制。     

溶剂效应和取代基效应对2-(2-氨基苯基)苯并噻唑光谱性质及激发态分子内质子转移的影响

合成了多种2-(2-氨基苯基)苯并噻唑(APBT)氨基氢原子被供电子及吸电子基团取代的衍生物, 并用紫外光谱﹑荧光光谱等方法和密度泛函理论(DFT)计算研究了溶剂效应和取代基效应对衍生物的光谱性质及激发态分子内质子转移(ESIPT)的影响规律. 结果表明, 相比于非极性溶剂环己烷, 随溶剂极性的增加及APBT-溶剂分子间氢键的形成, APBT的紫外-可见最大吸收峰和荧光最大发射峰均发生了一定程度的红移, 并对APBT的ESIPT产生了影响. 在APBT分子的氨基氮原子上引入不同的吸电子或斥电子取代基, 对氮原子的电荷性质有较大的影响. 在环己烷溶剂中, 甲基取代后的APBT仅有单重荧光发射峰, 体系未发生ESIPT过程; 而COCH₂Cl等吸电子基团能促进APBT的ESIPT, 其荧光发射光谱出现了明显的双重峰, 表明体系发生了激发态分子内质子转移反应. 量子化学的理论计算较好地验证了光谱实验结果.