疏水作用对光化学和光物理过程的影响 Ⅱ.不良溶剂中长链水杨酸烷基酯的簇集和荧光光谱的变化

前文报道了长链β-萘甲酸烷基酯在不良溶剂中形成激基缔合物,为长链分子在不良溶剂中发生簇集提供了新的证据.本文报道证明长链分子在不良溶剂中发生簇集的另一个实验事实.长链水杨酸烷基酯在二甲基亚砜-水(DMSO-H_2O)和乙二醇-水(EG-H_2O)混合溶剂中的荧光光谱分布以及荧光量子产率与短链水杨酸烷基酯的显著不同,这些差别可以用长链分子发生簇集来加以解释.     

疏水作用对光化学和光物理过程的影响 I: 不良溶剂中长链β-萘甲酸烷基酯的簇集和激基缔合物的形成

研究了不同链长的β-萘甲酸烷基酯(An)在乙二醇-水(EG-H2O)和二甲基砜-水(DMSO-H2O)混合溶剂中的荧光光谱, 以及添加物(无机盐、长链饱和烷烃、糖淀粉)对An荧光的影响. 长链An在混合溶剂中很容易形成激基缔合物, 表明疏水作用促使长链分子相互簇集. 测定了不同链长的分子发生簇集的临界浓度和临界溶剂组成. 分别添加长链烷烃和糖淀粉都能引起激基缔合物的荧光强度减弱和单体荧光强度的增强, 表明An和长链烷烃共簇集, 与糖淀粉形成包结物. 研究了在簇集体中An形成激基缔合物的动力学和热力学, 测定了激基缔合物形成和解离速率常数、活化能和热焓的变化. 证明了簇集体中基态发色基团之间并不具有激基缔合物的构型, 在一定温度下, 簇集体会发生相变.     

疏水作用对光化学和光物理过程的影响 Ⅰ.不良溶剂中长链β-萘甲酸烷基酯的簇集和激基缔合物的形成

本文研究了不同链长的β-萘甲酸烷基酯(A_n)在乙二醇-水(EG-H_2O)和二甲基砜-水(DMSO-H_2O)混合溶剂中的荧光光谱,以及添加物(无机盐、长链饱和烷烃、糖淀粉)对A_n荧光的影响.长链A_n在混合溶剂中很容易形成激基缔合物,表明疏水作用促使长链分子相互簇集.测定了不同链长的分子发生簇集的临界浓度和临界溶剂组成.分别添加长链烷烃和糖淀粉都能引起激基缔合物的荧光强度减弱和单体荧光强度的增强,表明A_n和长链烷烃共簇集,与糖淀粉形成包结物.研究了在簇集体中A_n形成激基缔合物的动力学和热力学,测定了激基缔合物形成和解离速率常数、活化能和热焓的变化.证明在簇集体中基态发色基团之间并不具有激基缔合物的构型.在一定温度下,簇集体会发生相变.     

疏水作用对光化学和光物理过程的影响 Ⅶ.芘基烷基酮的荧光光谱及其在不良溶剂中的簇集

溶剂的极性对芘基烷基酮的单体荧光和激基缔合物荧光有很大影响,在非极性溶剂中单体荧光很弱,随着溶剂极性增大,单体荧光增强,单体荧光和激基缔合物荧光明显红移。利用芘基烷基酮荧光的这些性质研究了长链分子在二甲基亚砜-水(DMSO-H₂O)中的簇集现象。在浓度非常低的情况下,长链芘基烷基酮发射激基缔合物荧光,单体荧光也明显蓝移,表明芘基烷基酮形成了簇集体。长链饱和烷烃和芘基烷基酮发生共簇集,簇集体内的极性比环己烷的极性稍大。     

疏水作用对光化学和光物理过程的影响——Ⅷ.N-烷基吲哚在不良溶剂中的簇集及其荧光光谱

本文研究了链长不同的N-烷基吲哚和3-甲基-N-烷基吲哚在二甲基亚砜-水(DMSO-H_2O)混合溶剂中的稳态和时间分辩荧光光谱,发现随混合溶剂中水的体积分数增大、短链吲哚衍生物的荧光峰位置红移。荧光寿命增长、而长链吲哚衍生物荧光峰位置明显兰移、荧光寿命变短。表明长链吲哚衍生物在混合溶剂中发生簇集,簇集体中微环境的极性和环己烷相似,利用时间分辨荧光光谱计算出长链吲哚衍生物在溶液本体相和簇集体中的分布。     

疏水作用对光化学和光物理过程的影响——Ⅷ.N-烷基吲哚在不良溶剂中的簇集及其荧光光谱

本文研究了链长不同的N-烷基吲哚和3-甲基-N-烷基吲哚在二甲基亚砜-水(DMSO-H_2O)混合溶剂中的稳态和时间分辩荧光光谱, 发现随混合溶剂中水的体积分数增大、短链吲哚衍生物的荧光峰位置红移。荧光寿命增长、而长链吲哚衍生物荧光峰位置明显兰移、荧光寿命变短。表明长链吲哚衍生物在混合溶剂中发生簇集,簇集体中微环境的极性和环己烷相似, 利用时间分辨荧光光谱计算出长链吲哚衍生物在溶液本体相和簇集体中的分布。     

疏水作用对光化学和光物理过程的影响IX. 长链分子的簇集对β-萘甲酸烷基酯和脂肪酸9-蒽甲醇酯间能量传递的增强作用

在二甲基亚砜-水(DMSO-H2O)混合溶剂中, 长链β-萘甲酸烷基酯(An)、长链脂肪酸9-蒽甲醇酯(En)和长链饱和烷烃(Cn)相互簇集形成共簇集体, An通过共振机制向En进行单重态能量传递, 在每个簇集体含近一个给体分子和一个受体分子的情况下, 能量传递效率高达50%,簇集体内能量抟递的速度比簇集体同的大一个数量级, An激基缔合物也可向En进行能量传递, 但效率很低, 由于形成激基缔合物的过程与能量传递过程相互竞争, 激基缔合物的形成降低了能量传递的效率。     

疏水作用对光化学和光物理过程的影响IX. 长链分子的簇集对β-萘甲酸烷基酯和脂肪酸9-蒽甲醇酯间能量传递的增强作用

在二甲基亚砜-水(DMSO-H2O)混合溶剂中, 长链β-萘甲酸烷基酯(An)、长链脂肪酸9-蒽甲醇酯(En)和长链饱和烷烃(Cn)相互簇集形成共簇集体, An通过共振机制向En进行单重态能量传递, 在每个簇集体含近一个给体分子和一个受体分子的情况下, 能量传递效率高达50%,簇集体内能量抟递的速度比簇集体同的大一个数量级, An激基缔合物也可向En进行能量传递, 但效率很低, 由于形成激基缔合物的过程与能量传递过程相互竞争, 激基缔合物的形成降低了能量传递的效率。     

疏水作用对光化学和光物理过程的影响——Ⅸ.长链分子的簇集对β-萘甲酸烷基酯和脂肪酸9-蒽甲醇酯间能量传递的增强作用

在二甲基亚砜-水(DMS0-H_2O)混合溶剂中,长链β-萘甲酸烷基酯(A_n)、长链脂肪酸9-蒽甲醇醣(E_n)和长链饱和烷烃(C_n)相互簇集形成共簇集体,A_n通过共振机制向E_n进行单重态能量传递。在每个簇集体含近一个给体分子和一个受体分子的情况下,能量传递效率高达50％。簇集体内能量传递的速度比簇集体间的大一个数量级。A_n激基缔合物也可向E_n进行能量传递,但效率很低。由于形成激基缔合物的过程与能量传递过程相互竞争,激基缔合物的形成降低了能量传递的效率。     

疏水作用对光化学和光物理过程的影响 Ⅻ.2-羟基-4-烷氧基二苯甲酮在不良溶剂中的簇集

测定了2-羟基-4-甲氧基二苯甲酮(HMDB)和2-羟基-4-辛氧基二苯甲酮(HODB)在良溶剂和不良溶剂中的吸收光谱。在不良溶剂(乙二醇-水的混合溶剂)中,带长链的HODB发生簇集。由于簇集体内极性较小,HODB的吸收光谱与其在环己烷中相似。HMDB不发生簇集。     

Hydrophobic effects on photophysical and photochemical processes: 1. Aggregation and excimer formation of alkyl β-naphthoates with long chain in poor solvents

The fluorescence spectra of alkyl β-naphthoates with various chain lengths (A_n) in DMSO-H₂O and ethylene glycol-water (EG-H₂O) mixtures were studied. The β-naphthoates with short chain show monomer fluorescence only in both solvent mixtures, while fluorescence spectra of long chain alkyl β-naphthoates are dominated by excimer emission. Addition of long chain hydrocarbon or amylose resulted in the reduction of excimer emission and enhancement of monomer fluorescence. All these experimental results supported intermolecular aggregation of long chain alkyl β-naphthoates in poor solvents. The kinetic parameters of the formation and dissociation of excimer as well as fluorescence polarization in aggregates were measured. These data provided an insight into the characteristics of aggregates.     

Surface and fluorescence properties of a novel fluorescent surfactant

A novel kind of fluorescent surfactant having 7-hydroxylcoumarin group in the long alkyl chain was synthesized. The critical micelle concentration (CMC), surface tension (γ_cmc) at CMC and absorption, fluorescence properties of this product were determined. From the variations of fluorescence spectra in different solvents, it is observed that the polarity and dielectric constant of the solvents play important roles in the maximum fluorescence intensity and wavelength. Moreover, the surprised exhibition of two fluorescence bands in neutral and alkaline solutions has been attributed to the superexciplex formation of the product molecules. Also, the lower product concentration measuring the fluorescence properties as well as the supposed configuration of hydrogen bond of the product indicate that the larger aggregations cannot exist in alkaline solutions. The superexciplex is a possibility with two or more polar excited molecules together to form an excited state association.     

Spectroscopic studies of a near-infrared absorbing pH sensitive aminodienone-carbocyanine dye system

Synthetic red and near-infrared absorbing dyes may be used as probe molecules in a large number of applications. Dyes exhibiting spectral changes with hydrogen ion concentration are useful as pH probes. Those dyes which have their absorption and fluorescence maxima in the long wavelength region of the visible spectral region are specially valuable because of decreased interference and semiconductor laser applications. In this paper we have evaluated an aminodienone dyes 1 which demostrates pH dependent absorption and fluorescence spectra as well as solvent polarity dependence. In organic solvents the long wavelength absorption band of the dye is in the reduced interference region. The absorption maximum is at 535 nm in neutral or alkaline solutions in methanol. The absorption spectra undergo a strong bathochromic shift in the presence of acids (lambda(max) = 709 nm) with a concomitant change in the fluorescence spectra. This pH sensitive dye was found to be specially especially useful for organic solvents. The analytical utility of this and similar near-infrared absorbing dyes is discussed.     

A novel fluorophore with dual fluorescence: local excited state and photoinduced electron-transfer-promoted charge-transfer state.

Absorption and emission spectra of 9-N,N-dimethylaniline decahydroacridinedione (DMAADD) have been studied in different solvents. The fluorescence spectra of DMAADD are found to exhibit dual emission in aprotic solvents and single emission in protic solvents. The effect of solvent polarity and viscosity on the absorption and emission spectra has also been studied. The fluorescence excitation spectra of DMAADD monitored at both the emission bands are different. The presence of two different conformation of the same molecule in the ground state has lead to two close lying excited states, local excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the dye. A CTstate involving the N,N-dimethylaniline group and the decahy droacridinedione chromophore as donor and acceptor, respectively, has been identified as the source of the long wavelength anomalous fluorescence. The experimental studies were supported by ab initio time dependent-density functional theory (TDDFT) calculations performed at the B3LYP/6-31G* level. The molecule possesses photoinduced electron transfer (PET) quenching in the LE state, which is confirmed by the fluorescence lifetime and fluorescent intensity enhancement in the presence of transition metal ions.     

Tuning the Nature of the Fluorescent State: A Substituted Polycondensed Dye as a Case Study

An extensive spectroscopic analysis is presented of an elongated polycondensed dye with a donor–acceptor substitution. The charge‐transfer (CT) state, polarized along the long molecular axis, is close in energy to a local excitation (LE) of the polycondensed system, roughly polarized along the short molecular axis, which makes this system particularly suitable to investigate the subtle LE/CT interplay. An essential‐state model is presented that quantitatively reproduces absorption and fluorescence spectra, as well as fluorescence emission and excitation anisotropy spectra collected in solvents of different polarity and viscosity, which sets a sound basis for the understanding of how solvent polarity and solvent relaxation affect the nature of low‐lying excitations. The markedly different fluorescence emission and excitation anisotropy spectra measured in glassy and liquid polar solvents unambiguously demonstrate the major role played by solvent relaxation in the definition of fluorescence properties of the dye.     

Temperature-sensitive dendritic micelles

Syntheses up to three generations have been achieved of biaryl-based amphiphilic dendrons with a charge-neutral pentaethylene glycol as the hydrophilic part and a decyl chain as the hydrophobic part. Studies on the temperature-dependent characteristics revealed that these dendrons exhibit a generation-dependent lower critical solution temperature (LCST). This behavior is attributed to the combination of the amphipathic nature of the hydrophilic pentaethylene glycol side chain and dendritic effect. Interestingly, this biaryl-based scaffold also maintains the ability to form a micelle-like assembly in polar solvents and an inverted micelle-like assembly in apolar solvents. Polarity of the dendritic interior was investigated using dye-based microenvironment studies. The aggregation behavior of these micelles was analyzed by fluorescence spectroscopy and dynamic light scattering. Critical micelle concentrations (CMC) of these assemblies were investigated using fluorescence excitation spectra of the sequestered guest molecule, pyrene.     

具有不同长度间隔基的含联苯基团的侧链液晶聚炔的荧光行为(英文)

对一系列具有不同长度间隔基的含联苯基团的侧链液晶聚炔的稳态荧光和荧光衰减行为进行了研究.为便于比较,选取其中一个单体作为模型化合物.稳态荧光光谱结果表明,聚合物和单体均显示一个荧光发射,该荧光发射来源于聚合物侧链的联苯基团.随着间隔基长度的减小,聚合物的荧光强度降低.荧光衰减结果表明单体的荧光衰减可以拟合为一个单指数衰减,而聚合物的荧光衰减拟合为三指数衰减.这种三指数衰减可能由溶液局部高浓度引起的猝灭和侧链联苯基团的旋转受阻所引起.溶剂效应表明,溶剂与联苯基团之间的相互作用随溶剂极性增加而增大.