Solvent Effect on the Fluorescence and Phosphorescence of Morphine and its Model Compounds

In the fluorescence spectra only morphine exhibits large red shifts of the maxima on increasing solvent polarity. In the phosphorescence spectra, phenol, anisole, and 3-methoxyphenol exhibit large red shifts of the maxima on going from nonpolar to polar solvents. For the latter, the results are interpreted in terms of charge-transfer-to-solvent (CTTS) transitions. For morphine, 2- and 4-methoxyphenol, the phosphorescence maxima occur at long wavelengths in both nonpolar and polar solvents, and this is interpreted in terms of CTTS and intramolecular charge transfer processes. The red-shift of the morphine fluorescence band on going to polar solvents is similarly interpreted as a combination of CTTS and intramolecular charge transfer transitions.     

Spectroscopic and theoretical evidence for the photoinduced twisted intramolecular charge transfer state formation in N,N-dimethylaminonaphthyl-(acrylo)-nitrile

The phenomenon of excited state twisted intramolecular charge transfer (TICT) process in N,N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN) has been reported on the basis of steady-state absorption and fluorescence spectroscopy in combination with quantum chemical calculations. The absorption and fluorescence characteristics of DMANAN in solvents of different polarity reveal the presence of a single species in the ground state which forms the intramolecular charge transfer state upon photoexcitation. The observed dual fluorescence is assigned to a high-energy emission from the locally excited or the Franck-Condon state and the red-shifted emission from the charge transfer (CT) state. In polar protic solvents, hydrogen-bonding interaction on CT emission has been established from the linear dependency of the position of the low-energy emission maxima on hydrogen-bonding parameter (α). The experimental findings have been correlated with the theoretical results based on TICT model obtained at density functional theory (DFT) level. The theoretical potential energy surface for the first excited state along both the donor and acceptor twist coordinates in the gas phase obtained by time dependent density functional theory (TDDFT) method and in polar solvent by time dependent density functional theory-polarized continuum model (TDDFT-PCM) method predicts well the experimental spectral properties.     

Fluorescence Properties of Donor–Acceptor-Substituted Pyrazoloquinolines

The photophysical properties of three newly synthesized pyrazoloquinolines, composed of N,N-dimethylaniline as donor subunit and various substituted forms of the acceptor pyrazoloquinoline (DPPQ), were investigated by absorption as well as by stationary and time resolved fluorescence spectroscopy. These compounds show generally highly efficient emission in nonpolar and medium polar solvents; the dipole moment of the emitting state increases and the quantum yield decreases with solvent polarity. These results are explained by state reversion in polar solvents: At low polarities emission originates from a state localized on the DPPQ moiety, whereas in the high-polarity regime the next excited state of charge transfer character, in which an electron is promoted from the amino nitrogen lone pair into an excited orbital of the DPPQ moiety, becomes the fluorescent state. This view is corroborated by semiempirical calculations including the solvent reaction field, low-temperature fluorescence measurements, and the observation of effects of protonation on the spectroscopic and photophysical properties.     

有机添加物对7-胺基香豆素分子发光的增强效应

测定了在有卤代苯等存在时,一些7-胺基香豆素在不同溶剂中的吸收和发射谱及荧光寿命。所得结果表明,具有给电子能力的有机添加物可对非刚性7-胺基香豆素衍生物在极性溶剂中的荧光起增强作用。基于荧光衰变动力学的分析及添加物的荧光增强能力与其氧化电位的线性关系,提出荧光增强作用的机理是添加物通过分子间电荷转移作用使香豆素分子激发态不发光的TICT态向发光的ICT态转化所致。     

香豆素—1的荧光介质效应

详细研究了香豆素－１在环己烷－醇、１，４－二氧六环－水二元溶剂及环糊精，表面活性剂溶液体系中的荧光光谱。通过溶剂－溶质分子间氢键作用及对其非荧光性的ＴＩＣＴ态形成的影响。讨论了这种荧光探针的荧光光谱对环境极性非常敏感的原因，测定了它与环糊精的包结常数和与表面活性剂胶束的结合常数。     

Solvent Polarity and Excitation Wavelength Dependence of the Dual Fluorescence in N,N-Diethyl-4-Nitrosoaniline

Dual fluorescence in N,N-Diethyl-4-nitrosoaniline (DENA) has been studied employing absorption, excitation and emission spectroscopic techniques and computational methods. The absorption and fluorescence spectra of DENA were measured in solvents of various polarities at room temperature. The emission spectra of DENA were found to exhibit a single emission band in non polar solvent (cyclohexane) and in a highly polar solvent (acetonitrile). In the contrary, two emission bands were observed in medium polar solvents (tetrahydrofuran, 1,2-dichloroethane and dichloromethane) whereby the short (local excited; LE) and long (charge transfer; CT) emission maxima correspond to the emission maxima of the compound observed in cyclohexane and acetonitrile solutions, respectively. Moreover, the two emission bands have shown strong excitation wavelength dependence, and area normalization resulted in an iso-emissive point. The two emission maxima were in addition found to correspond to two excitation maxima in 3D fluorescence spectra. Further, two minima were obtained in potential energy surface calculation of DENA. From the experimental and computational results it was concluded that the dual fluorescence may be attributed to the presence of two different ground state structural conformers of DENA in equilibrium that are stabilized through solute-solvent interaction.     

具有电子推拉结构的多支化分子的光物理特性的研究

利用稳态光谱和飞秒时间分辨荧光亏蚀的技术,研究了不同溶剂中一系列有分子内电荷转移特性的分子的结构与光物理性质的关系,研究体系为三苯胺作为电子给体,2,1,3-苯并噻二唑作为受体的单支分子及其对应的两支和三支分子. 并结合TD-DFT计算进一步解释了实验中所观察到的现象. 三个分子相似的吸收和荧光光谱以及强的溶剂依赖光谱特性表明两支与三支分子激发态与单支分子相似,表明激发态都定域在其中一支上. 激发时多支分子内发生多维电荷转移,然后快速地定域到某一支上发射. 另一方面多支分子相对于单支分子吸收和发射光谱的红     

Intra- and intermolecular proton transfer in methyl-2-hydroxynicotinate

Spectral characteristics of methyl 2-hydroxynicotinate (MEHNA) have been studied using absorption, fluorescence excitation and fluorescence spectroscopy, as well as, using single photon counting nanosecond spectrofluorimeter. MEHNA is present as enol in less polar solvents and keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to phototautomer, formed by excited state intramolecular proton transfer (ESIPT), whereas fluorescence is only observed from keto form in polar solvents. In aqueous and polar solvents monocation (MC) is formed by protonating the exo carbonyl oxygen atom in the ground state (S₀) and in the first excited singlet state (S₁), MC is obtained by protonating carbonyl oxygen atom of the ester. It is formed by ESIPT from exo carbonyl proton to carbonyl oxygen atom of the ester. Dication is formed by protonating both the oxygen atoms. Two kinds of monoanions formed by deprotonating phenolic proton or >N-H proton of keto suggest the presence of enol and keto in aqueous solution. In cyclohexane MC is formed by protonating carbonyl oxygen in both S₀ and S₁ states. The electronic structure calculations were performed on each species using semi-empirical quantum mechanical AM1 method and density functional theory B3LYP with 6-31G^** basis set using Gaussian 98 program, along with potential energy mapping, to characterize the particular species.     

Estimation of Excited State Dipolemoments from Solvatochromic Shifts–Effect of pH

Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.     

Excited-state inter- and intramolecular proton transfer in methyl 3-hydroxy-2-quinoxalinate: effects of solvent and acid or base concentrations

Absorption, fluorescence excitation and fluorescence spectroscopy, combined with time-dependent spectroscopy and semi-empirical (AM1) and density functional theory using Gaussian 98 program calculations have been used to study the effects of solvent and acid or base concentration on the spectral characteristics of methyl 3-hydroxy-2-quinoxalinate (M3HQ). M3HQ is present as enol in less polar solvents and as keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to the phototautomer, formed by the excited-state intramolecular proton transfer, whereas fluorescence is only observed from keto in the polar solvents. In aqueous and polar solvents the monocation (MC5/MC6) is formed by protonating the carbonyl oxygen atom in the ground (S₀) and the first excited singlet states (S₁). Dication is formed by protonating one of N- atom of MC5/MC6. Monoanion is formed by deprotonating the phenolic proton of enol in the basic solution. pK_a values for different prototropic equilibriums were determined in S₀ and S₁ states and discussed.     

Spectroscopic Studies of Fluorenone Derivatives

The absorption and steady-state fluorescence spectra of fluorenone, 1-hydroxyfluorenone, and 3-dimethylaminofluorenone have been obtained for various concentrations in a series of non-polar and polar solvents. The substituents (-OH and -N(CH₃)₂) as the electron-donating functional groups cause a large shift of the longwave absorption band and Stokes' shift of the monomer- and excimer-fluorescence bands in comparison with fluorenone. The total emission spectrum of 3-dimethylaminoflourenone in polar aprotic solvents exhibits a new band at 500 nm originating form the emission of the twisted intramolecular charge transfer (TICT) isomer. The excited state dipole moments of the emiting species of the molecule studied are determined using the solvatation shift method and calculated values of the ground state dipole moments.     

Excited and ground state conformations of p-dimethylamino-benzaldehyde and p-dimethylaminoacetophenone

p-dimethylaminobenzaldehyde (DMABA) and p-dimethylaminoacetophenone (DMAA) were investigated in nonpolar and polar protic and aprotic solvents over a wide temperature range. The sequence of the lower lying excited states was established. The temperature dependence of the fluorescence yields was interpreted within the irreversible reaction kinetics scheme b¹→TICT (twisted internal charge transfer) state. The activation energies and the rate constants were evaluated. Differences between the low-temperature fluorescence or phosphorescence excitation spectra and the absorption spectrum were found to be due to the existence of different rotamers in the ground state. Quantum chemical (INDO) calculations of the energies of electronic transitions, oscillator strengths and dipole moments were performed for flat and twisted conformations of DMABA.     

2019年3期 电子期刊

通过Debus-Radziszewski、Suzuki-Miyaura和Knoevenagel缩合反应,设计合成了一种新型的咪唑衍生物L,并使用傅里叶变换红外光谱和核磁共振氢谱对合成化合物进行了结构表征。不同极性溶剂中光物理性质和密度泛函理论计算结果表明该系列化合物具有典型的分子内电荷转移（Intramolecular charge transfer,ICT）效应;紫外-可见吸收和荧光发射光谱证实它表现出聚集诱导猝灭（Aggregation-caused quenching,ACQ）性质。进一步的光物理性质测试表明化合物L在THF/H₂O混合溶液中可实现对2,4,6-三硝基苯酚（苦味酸,picric acid,PA）的检测,检测限为3.7×10^-6 mol/L。     

Theoretical study on twisted intramolecular charge transfer of 1-aminoanthraquinone in different solvents

The twisted intramolecular charge transfer and the excited state relaxation of 1-aminoanthraquinone(1-NH_2-AQ)in different solvents are investigated using quantum chemical calculations in this paper.The geometries of the ground state are optimized both in gas and solvents based on the high-level ab initio calculations,the lowest excited singlet state geometry is optimized only in gas for simplicity.An intramolecular charge transfer property is substantiated by the large change of dipole moments between the S_0 and S_1 states.The mechanism of twisted intramolecular charge transfer is proposed by the conformational relaxation on the potential surface of the S_1state.Quantum chemical calculations present that internal conversion and intersystem crossing are important approaches to the ultrafast deactivation of the S_1 state via the twisting of the amino group.The smaller energy difference between the S_0 and S_1 state shows that the internal conversion process is much faster in a polar solvent than in a nonpolar solvent.Energy intersections between the T_2 and S_1 state in cyclohexane and dioxane indicate a faster intersystem crossing process in them than in ethanol.These theoretical results agree well with the previous experimental results.Energy barriers are predicted on the potential surface of the S_1 state,and they have a positive correlation to solvent viscosity,and the timescale of twisted intra-molecular charge transfer in dioxane is predicted to be longer than in cyclohexane and ethanol.     

双光子吸收材料二苯乙烯衍生物的合成及光谱性质

设计、合成并用红外光谱、1H NMR、元素分析表征了三种用于双光子吸收材料的二苯乙烯衍生物,4,4′-双(二苯氨基-反式-苯乙烯基)联苯(BPSBP),4,4′-双(二乙氨基-反式-苯乙烯基)联苯(BESBP)和4,4′-双(9-咔唑基-反式-苯乙烯基)联苯(BCSBP)。实验结果表明三者最强的单光子吸收出现在350～400 nm之间,且单光子吸收和荧光光谱中表现出明显的溶剂化显色效应,揭示了分子内对称电荷转移的本质,双光子荧光光谱则揭示了单光子和双光子吸收具有相同的发射机理。利用双光子上转换荧光法测试发现,三种双光子吸收材料在800 nm飞秒激光的激发下具有较大的吸收截面,分别为892,617和483 GM,这表明在双光子领域有潜在的应用价值。     

A New Fluorescent Sensor Based on 1H-pyrazolo[3,4-b]quinoline Skeleton. Part 2

A novel fluorescent dye bis-(pyridin-2-yl-methyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amine (P1) has been synthesized and investigated by means of steady state and time-resolved fluorescence techniques. This compound acts as sensor for fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium, calcium, and zinc) in highly polar solvents such as acetonitrile. The mechanism which allows application of this compound as sensor is an electron transfer from the electron-donative part of molecule (amine) to the acceptor part (pyrazoloquinoline derivative), which is retarded upon complexation of the electro-donative part by inorganic cations. The binding constants are strongly dependent on the charge density of the analyzed cations. The 2/1 complexes of P1 with Zn(++) and Mg(++) cations posses large binding constants. Moreover, in the presence of these cations a significant bathochromic shift of fluorescence is observed. The most probable explanation of such behaviour is the formation of intramolecular excimer. This is partially supported by the quantum chemical calculations.     

Fluorescence Characteristics of Schiff Bases Derived from Amino- and Aminoalkylpyridines

The fluorescence characteristics of the Schiff bases 2-(3-pyridylmethyliminornethyl)phenol (1), 2-(2 pyridyliminomethyl)phenol (2), N.N-bis(salicylidene)-2,3-pyridinediamine (3), N,N'-bis(salicylidene)-2,6-pyridinediamine (4) and 2-(2-amino-4-methoxymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (5) were studied in various solvents at different pH values. Corresponding quantum efficiencies were determined. Compound 1, which showed a tendency towards tautomeric mterconversion to ketoamine in polar protic solvents, was not fluorescent at pH < 8. The fluorescence of other compounds was very sensitive to solvent polarity and the pH of the medium. Compounds 2-4, preferably present as enolimines in all solvents, were not fluorescent in non-polar and moderately polar solvents, whereas weak emission was observed in polar solvents, like methanol, dimethylformamide and dioxane/water 1/1 (0.001 < Q < 0.072). A significant increase in Stokes shifts and in quantum efficiencies was noted as a result of increasing polarity of dioxane/water mixtures, indicating specific interactions with polar water molecules. The emission was promoted at acidic pH values where a pyridinium cation was formed (0.061 < Q < 0.519, in dioxane/water 1/1 at pH 3.4). Compound 5, which was a tautomeric mixture of enoiimine and cyclic diamine in all solvents, was fluorescent in polar as well as in non-polar media. The quantum efficiency varied dependent on the solvent and pH (0.023 <Q< 0.435). The cyclic diamine, i. e. the more rigid structure was supposed to be responsible for the fluorescence in non-polar and aprotic solvents as well as at neutral, and weakly basic pH values.     

激发态质子转移分子2-（2′-羟基苯基）苯并噻唑在不同溶剂中的光谱特性

观测了2-（2′-羟基苯基）苯并噻唑（HBT）在不同极性溶剂中的吸收光谱和荧光光谱,详细研究了溶剂极性对HBT发生激发态分子内质子转移（ESWT）影响的机制。吸收光谱表明在常态条件下,HBT在各种溶剂中都以烯醇式构型和酮式构型共同存在,但以烯醇式构型占绝大多数。荧光光谱表明在纯环己烷溶剂中,HBT被紫外光激发时,绝大多数烯醇式构型发生ESIPPT转变为酮式构型,分子的ESIPT效率最大。在含有乙醇的极性溶剂中,HBT烯醇式会形成溶剂化的烯醇式构型,阻碍分子发生ESIPT反应。溶剂中乙醇含量愈多极性愈强,溶剂化烯醇式的成份就愈多,HBT的ESIPT效率就愈低。以400nm光激发HBT溶液时,在510nm处发现酮式构型荧光,从而确认了400nm处的弱吸收是酮式构型的吸收;且在436和456nm处还有新的荧光峰,分析其可能来源于酮式构型去质子化阴离子的发射。     

激发态质子转移分子2-(2'-羟基苯基)苯并噻唑在不同溶剂中的光谱特性

观测了2-(2’-羟基苯基)苯并噻唑(HBT)在不同极性溶剂中的吸收光谱和荧光光谱,详细研究了溶剂极性对HBT发生激发态分子内质子转移(ESIPT)影响的机制。吸收光谱表明在常态条件下,HBT在各种溶剂中都以烯醇式构型和酮式构型共同存在,但以烯醇式构型占绝大多数。荧光光谱表明在纯环己烷溶剂中,HBT被紫外光激发时,绝大多数烯醇式构型发生ESIPT转变为酮式构型,分子的ESIPT效率最大。在含有乙醇的极性溶剂中,HBT烯醇式会形成溶剂化的烯醇式构型,阻碍分子发生ESIPT反应。溶剂中乙醇含量愈多极性愈强,溶剂化烯醇式的成份就愈多,HBT的ESIPT效率就愈低。以400 nm光激发HBT溶液时,在510 nm处发现酮式构型荧光,从而确认了400 nm处的弱吸收是酮式构型的吸收;且在436和456nm处还有新的荧光峰,分析其可能来源于酮式构型去质子化阴离子的发射。     

Spectral Properties and Solubilization Location of 2'-Ethylhexyl 4-(N,N-Dimethylamino)benzoate in Micelles

在阳离子、非离子和阴离子表面活性剂胶束溶液中,研究了4-(N,N-二甲氨基)苯甲酸2'-乙基己基酯(EHDMAB)的双重荧光和紫外吸收．当EHDMAB增溶在不同的胶束溶液中,紫外吸收增强,在离子型胶束溶液中,可观察到具有较长波长的EHDMAB分子内扭转电荷转移(TICT)荧光,相反,在非离子型胶束溶液中,可观察到具有较短波长TICT荧光,特别是位于阳离子胶束Stern层中的吡啶阳离子可强烈猝灭EHDMAB分子的双重荧光,所吸收的紫外辐射主要通过TICT荧光和非辐射去活化衰减．按照EHDMAB分子TICT荧光在有机溶剂中的极性依赖性,EHDMAB分子的4-(N,N-二甲氨基)在离子型胶束和非离子型胶束中处于不同的极性环境;根据EHDMAB和表面活性剂分子的结构和大小分析,EHDMAB分子的4-(N,N-二甲氨基)应朝向胶束的极性头基团,而2'-乙基己基链则朝向疏水性的胶束内核．动态荧光猝灭测量为EHDMAB分子在不同胶束中的位置进一步提供了佐证．