一类新型分子内电荷转移荧光体——苯甲酰苯胺衍生物

评述了苯甲酰苯胺及其衍生物的发光行为和电荷转移/质子转移光物理模型的研究进展,并展望了该类新型分子内电荷转移荧光体在化学及生物分子识别与传感中的潜在应用前景.     

环己烷中苯甲酰苯胺的双重荧光--分子内电荷转移的直接光谱证据

自从O Connell等［1］报道苯甲酰苯胺(BA)在EPA玻璃体中异常的长波长荧光发射特性以来, 已有众多学者尝试解释该"异常"荧光的发射态性质［2～12］. Kasha等［2～7］认为长波长荧光是质子转移(PT)和电荷转移(CT)两种激发态发射的叠加, 而Azumaya等［8］则认为发射态只包含分子内扭转电荷转移(TICT)态. 应该指出的是, 在上述研究中, 电荷转移态的指认并无有力的实验事实, 而主要是依据与具有CT双重荧光的对二甲氨基苯甲氰［13,14］的类比. 显然, 有关苯甲酰苯胺的长波长荧光发射态的准确性质仍待实验阐明     

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.     

1-萘甲酰苯胺和2-萘甲酰苯胺的分子内电荷转移研究

A series of 1-naphthanilides (1) and 2-naphthanilides (2) with varied substituents at the para- or meta-position of anilino phenyl ring were prepared and their absorption and fluorescence spectra in a nonpolar solvent cyclohexane were investigated. An abnormal long wavelength emission assigned to the charge transfer (CT) state was found for all of the prepared naphthanilides in cyclohexane. A linear free energy correlation between the CT emission energies and the Hammett constants of the substituent was found within series 1 and 2. The value of the linear slope with 1 (0.42 eV) was higher than that with 2 (0.32 eV) being close to that of the substituted benzanilides 3 (0.31 eV) The higher slope value suggested higher charge separation extent in the CT state of 1 than that of 2. It was found that the corresponding linear slope of anilino-substituted benzanilides remained unchanged when para-, meta-, ortho-, or ortho, ortho-methyls were introduced into the anilino moiety, which ruled out the possible contribution of the difference in the steric effect and the electron accepting ability of the naphthoyl acceptor in 1 and 2. Compared with the early reported N-substituted-benzoyl-aminonaphthalene derivatives 4 and 5, it was considered that 1-naphthoyl enhanced the charge transfer in 1 and the proximity of its ^1La and ^1Lb states was suggested to be responsible. It was shown that 1- and/or 2-substituted naphthalene cores acting as either electron acceptor (naphthoyl) or electron donor (aminonaphthalene) were different in not only electron accepting (donating) ability but also shaping the charge transfer pathway.     

基于对二烷基氨基苯甲酰苯胺分子内电荷转移的单糖比值法荧光受体

Two dual fluorescent receptors (1 and 2) for monosaccharides based on 4-dialky(alkyl=methyl and n-butyl) containing boronic acid group at the amido aniline were synthesized and their spectral properties were investigated. These receptors exhibited dual fluorescence with the long-wavelength band displaying strong solvent-polarity dependence, indicating the occurrence of the excited-state intramolecular charge transfer （ICT).With increasing pH value in aqueous solutions, the hybridization of the boron atom changed from sp^2 to sp^3, inducing a decrease in the total fluorescence quantum yield. The experimental results indicated that the anionic form of the boronate group acted as an electron donor and the benzanilide-like charge transfer was promoted upon hybridization change. In the presence of monosaccharides, the boronic acid in 1 and 2 changed from neutral to anionic form. The intensity of the locally excited (LE) state emission decreased in the presence of sugars while a slight increase in the intensity at the charge transfer (CT) emission occurred. Based on the change in the CT to LE intensity ratios of 1 and 2 due to sugar binding, ratiometric fluorescent assays for monosaccharide sensing were established.     

二苯甲酰甲烷互变异构反应机理溶剂效应的理论研究

采用密度泛函B3LYP方法,在6-31+G(d,p)基组水平上对二苯甲酰甲烷质子转移引起的酮式-烯醇式互变异构反应机理进行了计算研究,获得了零点能、总能量、吉布斯自由能及质子转移过程的反应焓、活化能、活化吉布斯自由能和速率常数等参数.3种非质子溶剂中的优化和频率计算采用Onsager模型进行计算.计算结果表明,不论在气相还是3种溶剂中,二苯甲酰甲烷的烯醇式较酮式稳定,烯醇式向酮式气相转变需要较高的活化能垒,在不同极性的溶剂中,随着溶剂介电常数的增大,异构化反应活化能垒减小,反应速率常数增大.     

创新型综合实验:苯甲酰苯胺的合成*

肟化反应和贝克曼重排反应是高校化学专业重要的基础有机实验,现行的实验教材常采用由环己酮制备己内酰胺,该实验存在反应过程难监测,反应后处理损失大,收率低,实验效果不理想等问题。以二苯甲酮为原料,经肟化、贝克曼重排合成苯甲酰苯胺,产物经1H NMR、13C NMR、IR等确证分子结构。研究结果表明:苯甲酰苯胺合成反应平稳,实验现象明显,后处理简便,收率较高。通过TLC监测反应进程,能使学生对反应过程有清楚的认知和掌控。实验内容和时间适合大学实验要求,实验综合性强,拓展空间大,能够有效训练学生的创新思维和科研意识,提高学生的实验技能。     

ESIPT和TICT荧光发射的电子结构特征及发射能计算

采用含时密度泛函理论(TDDFT)与单激发组态相互作用(CIS)相结合的计算方案对八种结构相似的水杨酰苯胺衍生物及其类似物第一激发单重态(S1)进行考察, 证实它们的荧光发射分属分子内质子转移(ESIPT)和分子扭转-电荷转移(TICT)两种不同机制且结论与已知实验事实相符. ESIPT发光的化合物在电子跃迁前后无明显的电荷转移发生, 发射能计算的适用泛函是OLYP和BLYP等无Hartree-Fock(HF)交换成分的纯泛函; TICT发光的化合物在电子跃迁前后发生明显的电荷转移, 其适用泛函为含约37% HF交换成分的混合型泛函(例如mPW1B95和MPW1K). 按上述原则来选择适用泛函, 即可在TDDFT/6-31G(d)//CIS/3-21G(d)理论水平上正确预测水杨酰苯胺衍生物和类似物的发射能, 平均精度可达0.2 eV. 兼具质子转移与电荷转移双反应通道的化合物, 两者的竞争遵从能量最小原理, 结果使荧光发射仅选择其中一个通道进行. 泛函的选择只与实际发生的反应有关, 与并未实际发生的反应通道无关. 附加的八个算例进一步表明, 此成功的计算方案可望推广应用于其它类型的ESIPT和TICT荧光有机物.     

激发态分子内质子转移荧光探针的研究进展

荧光探针凭借其选择性好、灵敏度高、响应时间快、易于操作和检测限低等优点得到了广泛的关注。 激发态分子内质子转移(ESIPT)化合物具有特殊的激发态光物理过程,其显著的光物理性质是有较高的荧光量子产率及大的斯托克斯位移。 对于荧光分子而言,较大的斯托克斯位移可以减少自吸收和由内滤效应产生的干扰,增强分子的耐光性,有利于荧光的发射。 本文对ESIPT荧光探针检测离子(包括金属阳离子和阴离子)、中性小分子和生物大分子的研究进展进行阐述,并对ESIPT荧光分子的存在问题和应用前景进行评述。     

基于联合荧光机制的激发态分子内质子转移荧光探针研究进展

荧光探针能够实现对分析物的快速检测,并因其优异的选择性、高灵敏度和操作简便等优点成为近年的研究热点.激发态分子内质子转移(ESIPT)是最基础的荧光设计策略之一,基于ESIPT原理设计的荧光探针具有发光强度高、Stokes位移大以及反应过程可逆等优点,但也存在对环境敏感、发射波段较短等不足.近年来,将ESIPT与其它荧...     

Fluorescence Lifetimes of NIR-Emitting Molecules with Excited-State Intramolecular Proton Transfer

Molecular probes based on the excited-state intramolecular proton-transfer (ESIPT) mechanism have emerged to be attractive candidates for various applications. Although the steady-state fluorescence mechanisms of these ESIPT-based probes have been reported extensively, less information is available about the fluorescence lifetime characteristics of newly developed NIR-emitting dyes. In this study, four NIR-emitting ESIPT dyes with different cyanine terminal groups were investigated to evaluate their fluorescence lifetime characteristics in a polar aprotic solvent such as CH₂Cl₂. By using the time-correlated single-photon counting (TCSPC) method, these ESIPT-based dyes revealed a two-component exponential decay (τ₁ and τ₂) in about 2–4 nanoseconds (ns). These two components could be related to the excited keto tautomers. With the aid of model compounds (5 and 6) and low-temperature fluorescence spectroscopy (at −189 ℃), this study identified the intramolecular charge transfer (ICT) as one of the major factors that influenced the τ values. The results of this study also revealed that both fluorescence lifetimes and fractional contributions of each component were significantly affected by the probe structures.     

正己烷中对二烷基氨基苯甲酸的分子内电荷转移双重荧光

在非极性溶剂正己烷中,观察到了系列对二烷基氨基苯甲酸的双重荧光.皮秒激光诱导时间分辨荧光和溶剂极性效应研究证实:该双重荧光系由于激发态分子内电荷转移过程形成的电荷转移态和局部激发态所发射.超快反应动力学研究表明:在非极性溶剂中,对二烷基氨基苯甲酸分子内电荷转移过程是由较低的反应活化能所致.     

Studies on Intramolecular Charge Transfer Fluorescence Probe and DNA Binding Characteristics

An intramolecular charge transfer fluorescence probe of 4′-N,N-dimethylamino-4-amino-chalcone(DMAC) exhibits characteristics clearly correlated with the polarity of solvents. The interaction of this fluorescence probe with calf thymus DNA has been investigated. Generally, DMAC bound to DNA shows marked changes in fluorescence and absorbance properties compared to the spectral characteristics of the free form in solution phase. In the presence of DNA the fluorescence intensity of DMAC is greatly increased with a large bathochromic shift of excitation and emission wavelengths. A hypochromism in absorption spectrum was also observed. The absorption and fluorescence spectra, salt concentration effect, and KI quenching experiments demonstrate that DMAC molecule as an intercalator is inserted into the base-stacking domain of DNA double helix, and the interaction of the nucleobases with DMAC molecule causes the increase of fluorescence intensity and hypochromism in absorption spectrum. The intrinsic binding constant and the binding site number were estimated to be 7.04 × 10⁶ mol L⁻¹ in base pairs and 0.065, respectively. The I/I₀ vs DNA concentration plot shows a linear range covering 1.98 × 10⁻⁶ to 2.08 × 10⁻⁴ mol L⁻¹ in base pairs which can be used for determining DNA with a detection limit of 6.0 × 10⁻⁷ mol L⁻¹ in base pairs (0.6 μg ml⁻¹).     

基于激发态分子内质子转移的新一代荧光探针

对被誉为多参数、多功能的第二代荧光探针3-羟基黄酮类衍生物的光物理特性及其在微环境极性、微相变和相分离、膜电位测定等方面的实际应用做了比较详尽的介绍.     

黄芩素激发态分子内质予转移耦合电荷转移反应的实验和理论研究

通过稳态光谱实验和量子化学计算相结合,研究了黄芩素激发态质子转移耦合电荷转移的反应. 实验和计算中S1态吸收峰的缺失表明S1态是暗态. S1暗态导致在实验中观察不到黄芩素在乙醇溶液中的荧光峰,且固体的荧光峰很弱. 黄芩素分子的前线分子轨道和电荷差异密度表明S1态是电荷转移态,然而S2态是局域激发态. 计算的黄芩素分子的势能曲线在激发态只有一个稳定点,这表明了黄芩素激发态分子内质子转移的过程是一个无能垒的过程.     

Chemical Sensing and Molecular Recognition Based on Photoinduced Intramolecular Charge Transfer Dual Fluorescence

Represented by 4-dimethylaminobenzonitrile (DMABN), the electron donor/acceptor substituted benzenes show photoinduced intramolecular charge transfer (ICT) dual fluorescence has been well-known.     

Excited‐State Proton Transfer and Intramolecular Charge Transfer in 1,3‐Diketone Molecules

The photophysical signature of the tautomeric species of the asymmetric (N,N‐dimethylanilino)‐1,3‐diketone molecule are investigated using approaches rooted in density functional theory (DFT) and time‐dependent DFT (TD‐DFT). In particular, since this molecule, in the excited state, can undergo proton transfer reactions coupled to intramolecular charge transfer events, the different radiative and nonradiative channels are investigated by making use of different density‐based indexes. The use of these tools, together with the analysis of both singlet and triplet potential energy surfaces, provide new insights into excited‐state reactivity allowing one to rationalize the experimental findings including different behavior of the molecule as a function of solvent polarity.     

Fluorescence Quenching in BODIPY Dyes: The Role of Intramolecular Interactions and Charge Transfer

The fluorescence properties of the BODIPY dye and its two meso‐substituted derivatives, tert‐butyl‐ and phenyl‐BODIPY , are rationalized. The non‐emissive behavior of the latter two are attributed to the energetically accessible low‐lying conical intersection between the ground state and the lowest excited singlet state. Both intramolecular non‐covalent interactions and excited state charge transfer character are identified as being crucial for ‘stabilizing’ the intersection and prompting the nonradiative decay. Similar crossing was located in the bare BODIPY dye, however, being energetically less accessible, which correlates well with the high fluorescence quantum yields of the parent dye.     

一种新的分子内电荷转移荧光探针测定牛血清白蛋白

基于一种新的分子内电荷转移荧光探针1-酮-2-(对二甲氨基苯亚甲基)-四氢萘(简称KDTN)与牛血清白蛋白的结合反应,提出了测定牛血清白蛋白的荧光分光光度法.在激发波长λex)为430 nm,最大发射波长(λem)为530 nm及选定的试验条件下,测定牛血清白蛋白的线性范围为6.8～204.0 mg·L-1,线性回归方程△F=0.583 6.ρ-1.791 7,相关系数为0.999 1,方法的检出限(3S/N)为0.4 mg·L-1,样品的加标回收率为99.9%～102.0%.     

分子内电荷转移化合物的合成

以对硝基甲苯和苯酚为原料,经重氮化和偶合反应合成了新的具有分子内电荷转移能力的偶氮化合物(1),其结构经UV,1H NMR和元素分析表征.