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 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。     

Phase Separation of Poly(N‐isopropylacrylamide) in Mixtures of Water and Methanol: A Spectroscopic Study of the Phase‐Transition Process with a Polymer Tagged with a Fluorescent Dye and a Spin Label

The thermoreversible phase transition of poly(N‐isopropylacrylamide) randomly labeled with a spin label, 4‐amino‐2,2′,6,6′‐tetramethylpiperidine 1‐oxide (TEMPO), and a fluorescent dye, 4‐(pyren‐1‐yl)butyl (PNIPAM‐Py‐T), in different H₂O/MeOH mixtures was studied by turbidimetry, continuous‐wave electron paramagnetic resonance spectroscopy (CW‐EPR), and fluorescence spectroscopy. The macroscopic phase diagram of PNIPAM‐Py‐T in H₂O/MeOH measured by turbidimetry was identical to those of poly(N‐isopropylacrylamide) (PNIPAM) and of TEMPO‐labeled PNIPAM (PNIPAM‐T) in H₂O/MeOH mixtures. However, distinct differences among the three polymers were detected in their solvent‐dependent EPR and fluorescence‐spectroscopic properties. The EPR spectra were analyzed in terms of the isotropic hyperfine coupling constants, which monitor the variation in environmental polarity of the radical labels occurring for the conformational transitions of the polymer as a function of temperature, as well as the correlation time for reorientation motion, the increase of which is indicative of the increased viscosity of the radical environment and interactions occurring between the radical and other surface groups of the precipitated polymer, if compared to the soluble polymer. The fluorescence of Py in PNIPAM‐Py‐T displayed contributions from isolated excited pyrenes (monomer emission) and from preformed pyrene ground‐state aggregates (excimer emission). The quantum efficiencies of monomer and excimer emission were monitored as a function of solvent composition. By the two experimental approaches, we demonstrate the profound influence of the PNIPAM‐attached pyrene units in increasing the hydrophobicity of the nanodomains formed upon heat‐induced precipitation of PNIPAM‐Py‐T.     

Hydrophobic effects on photophysical and photochemical processes: 4. The conformation of polymethylene bis-β-naphthoates in poor solvents and their intramolecular excimer

The fluorescence properties of polymethylene bis-β-naphthoates with various chain lengths (B_n) in poor solvents such as dimethyl sulfoxide-water (DMSO–H₂O) and ethylene glycol-water(EG–H₂O) were measured under stationary and nonstationary conditions at various temperatures. Hydrophobic interactions bring the two chromophores of B₃, B₄ and B₁₀ into sandwich arrangement in ground state, thus promote intramolecular excimer formation upon excitation. The perfect overlapping structure of B₂ can not be formed in ground state because of the eclipsed conformation of two methylene groups in such a sandwich arrangement. The favorable conformation of B₂ is the structure in which the two naphthyl rings are in proximity. The activation energy, enthalpy and entropy changes of excimer formation of B₂ were calculated from the fluorescence decay parameters.     

Fluorescent probe as reporter on the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes

To get some information on the aggregation behaviors of the products derived from different organotrialkoxysilanes, the hydrolysis-condensation processes of some organotrialkoxysilanes have been examined by means of pyrene as fluorescent probe. The organotrialkoxysilanes used in the research were n-octadecyltri-methoxysilane (ODTMS), n-octyltrimethoxysilane (OTMS), 3-glycidoxypropyltrimethoxysilane (GTMS), 3-methacryloxypropyltrimethoxysilane (MAPTMS), and propyltrimethoxy-silane (PTMS). The results show that pyrene as fluorescence probe can respond sensitively not only to the organization state of the hydrolysates but also to the change in the organization state during the condensation process. The organization states during the hydrolysis and condensation can be explained in terms of structures of the products. In the initial stage, the silanols with long organic chains are amphiphilic molecules, and such nature of the silanols can be compared to that of a surfactant. Therefore, the excimer emission of pyrene is extremely obvious because of such silanols being prone to form aggregates. In the case of silanols having short alkyl groups or epoxy groups, these silanols homogenously disperse in solution, which results in the appearance of an only monomer emission of pyrene. In the late stage, the fluorescence behavior of pyrene is also sensitive to structural evolution of the silicates. The fluorescence spectra of pyrene during the condensation of the silanols with short alkyl groups or epoxy groups are almost in silence, indicating that the condensation products, with a low condensation degree, homogeneously disperse in solution. For the silanols with long hydrophobic substituents in different lengths, the changes in fluorescence spectra of pyrene during the condensation are varied. Commonly, the excimer emission is noticeable, implying that the condensation products with high condensation degree inhomogenously disperse in solution. However, the relative excimer/monomer fluorescence intensity is alkyl chain-length dependent. The longer alkyl chains in the condensation products result in the appearance of the obvious excimer emission. These phenomena imply that the condensation degree of the products increases with the length of the alkyl chains. Additionally, the distorted spectrum of pyrene appears in the case of the organotrialkoxysilanes with side chain substituent, illustrating that the steric hindrance between the substituents can be monitored by fluorescence of pyrene. All these results are verified by the fluorescence-quenching measurements. The approach in the present study gives new insights into the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes and emphasizes the influence of the self-assembling behavior.     

Ratiometry of monomer/excimer emissions of dipyrenyl calix[4]arene in aqueous media

Variations in the ratio of monomer/excimer emissions from pyrenyl groups bound to a calix[4]arene through facing carboxamidomethyl substituents have been investigated in H₂O/CH₃CN mixtures. Above a level of 50% H₂O, monomer emission declines and the excimer emission concomitantly increases. DFT calculations support the argument that disruption of intramolecular NHO bonds by water results in a geometry, which favors contact of the pyrene units and thus a strong excimer emission. Addition of Fe(III) to a H₂O/CH₃CN (4:1, v/v) solution of 1 at pH 6.1 quenches both monomer and excimer emissions through electron transfer (eT) from excited pyrene to the metal ion.     

The effect of γ‐cyclodextrin addition in the self‐assembly behavior of pyrene labeled poly(acrylic) acid with different chain sizes

The interaction between poly(acrylic acid) polymers (PAA) of low‐ (2000 g/mol) and high‐ (450,000 g/mol) molecular weight (M_w) hydrophobically modified with pyrene (PAAMePy) and β‐ and γ‐cyclodextrins (β‐CD, γ‐CD) was investigated with fluorescent techniques. The interaction with β‐CD promotes little variation in the spectral and photophysical behavior of the polymer, whereas significant changes are observed upon addition of γ‐CD. The degree of inclusion (between the pyrene groups of the polymer and the cyclodextrins) is followed through the observation of the changes in the absorption, excitation (collected in the monomer and excimer emission regions) and emission (I_E/I_M ratio) spectra and from time‐resolved data. Within the studied range of γ‐CD concentration, the fluorescence decays of the long chain (high M_w) PAAMePy polymers were found tri‐exponential in the monomer and excimer emission regions in agreement with previous studies. In the case of the low M_w PAAMePy polymers, tri‐exponential decays were observed at the monomer and excimer emission wavelengths. However, when a γ‐CD concentration of 0.01 and 0.03 M is reached for, respectively, the low‐ and high‐labeled pyrene short chain (low M_w) polymers, the fluorescence decays in the excimer region become biexponential (two excimers) with no rising component, thus showing that all pyrene groups are encapsulated (and preassociated) into the γ‐CD cavity. In the case of the high M_w polymers, the addition of γ‐CD has been found to change the level of polymer interaction from pure intramolecular (water in the absence of cyclodextrin) to a coexistence of intra‐ with intermolecular interactions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1402–1415, 2008     

Microenvironmental control of photochemical reactions: II. Fluorescence quenching of naphthalene and 1,3-di-(α-naphthyl)propane by RNA and bases in aqueous methanol

The fluorescence quenching of naphthalene ( 2 ) and 1,3-di(α-naphythyl)propane ( 1 ) by RNA and bases in methanol-water (v:v = 1:1) binary solvents in the presence or absence of cyclodextrin (CD) has been investigated. The results show that both the monomer and excimer fluorescence of 1 can be quenched by these quenchers. The quenching and rates depend on the quencher and temperature. It is shown that there is a critical temperature (Tc) for each quencher. Below Tc, the excimer fluorescence spectra show vibrational structures and the Stern-Volmer plots are straight lines (for uracil and cytosine); while above the Tc, the vibrational structures disappear and the Stern-Volmer plots deviate from linearity and curve upward. The former is a static process; while the latter is a mixture of both static and dynamic processes. The addition of α-CD has no effect on the fine structure; whereas β-CD prevents the appearance of this structure efficiently. The quenching rates both for the monomer and excimer of 1 by bases except cytosine in the presence of β-CD at ambient temperature are not changed; the quenching of fluorescence of 1 by RNA in the presence of β-CD, however, is hindered. Time-resolved fluorescence study shows that the excimer fine structures appear from the zero time. The intensity of fine structures depend on the fraction of water (π) in binary solvents, and it is independent of the pH value of the solvents. It is suggested that bases and RNA induced aggregates (perhaps microcrystal) are formed, in which the motion of molecules 1 is limited.     

Microenvironmental effects of cyclodextrins I: Enhancement of intramolecular excimer formation of polymethylene-bisβ-naphthoate via inclusion with cyclodextrins

The effects of α-, β- and γ-cyclodextrins (CDs) on the fluorescence spectra of a series of polymethylene-bis-β-naphthoates (Bn) have been studied. It is observed that β-CD and γ-CD enhance Bn intramolecular excimer fluorescence, indicating the formation of two-to-one guest host inclusion complexes. The possible conformation of these inclusion complexes is discussed.     

Correlation of architecture with excimer emission in 100% pyrene‐labeled self‐assembled polymers

Pyrene was incorporated as pendant unit to side‐chain urethane methacrylate polymers having a short ethyleneoxy or a long polyethyleneoxy spacer segment. The short‐spacer pyrene urethane methacrylate was also incorporated either as block or random copolymer (1:9) along with polystyrene. The excimer emission was observed to be different for different polymers with the random copolymer exhibiting the lowest efficiency. But, the total quantum yield was highest (? = 0.58) for random copolymer due to the high emission coefficient of monomer compared to that of excimer. The polymer dynamics were compared by steady state emission and fluorescence decay in THF or THF/water (9:1) solvent mixture and films. The solid state decay profile showed decay without a rise time indicating presence of ground state aggregates. In THF/water (9:1), the decay profile at the excimer emission (500 nm) showed a rise time indicating dynamic excimers. The evolution of excimeric emission centred ～430 or ～480 nm as a function of temperature was also studied in THF/water (9:1). The I_E/I_M ratio for the λ_{343 nm} excitation exhibited steady increase with temperature with the block copolymer PS‐b‐PIHP exhibiting the highest ratio and highest rate of increase; whereas, the random copolymer PS‐r‐PIHP had the lowest I_E/I_M ratios. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Abnormal Fluorescence Behavior of Pyrene Functionalized Chitosan Films to Some Quenchers

Investigation of the fluorescence behavior of a pyrene functionalized chitosan film (PSC-CS) to some quenchers,including KI,CH3NO2 and Cu(NO3)2,has revealed that the monomer emission from the PSC-CS film increased rather than decreased,whereas the excimer emission decreased with the increase of time of duration after addition of KI or Cu(NO3)2.Both the increasing and decreasing processes could last as long as 20min to 40min,Unlike that observed in the system containing KI or Cu(NO3)2,for CH3NO2 system,both the monomer emission and the excimer emission increased with introduction of the quencher,but the excimer emission only started to increase after an hour-long induction period.The position of the excimer emission of the PSC-CS film did not change very much with addition of KI or Cu(NO3)2.However,addition of CH3NO2 made the excimer emission blue shifted for at least 20nm indicating formation of distorted excimers opr partially overlapped excimers.The fluorescence response of the film to external additions is sensitive but is low in selectivity.This property may make the film use as a novel sensing material for monitoring the purity of water.     

Aggregation of l,3-di(α-naphthyl)propane and di(α-naphthylmethyl)ether in aqueous binary solvents

The UV absorption and fluorescence spectra of 1,3-di (α-naphthyl) propane (1), di (α-naphthylmethyl) ether ( 2 ), and α-methylnaphthalene ( 3 ) in aqueous methanol, ethanol, and DMSO were recorded as a function of π value (fraction of water in binary solvents). The existence of two states, a metastable state (defined as m) and a stable stationary state (defined as s), of molecules 1 as well as 2 in the above cosolvents at high π was shown by the contrary fluorescence excimer to monomer intensity (I_e/I_m) vs. π relationships of the samples prepared with different processes. On the basis of the π value, substrate concentration, and the temperature dependence of the UV spectra, fluorescence excitation and emission spectra, the chromophores of 1, 2 show the formation of aggregates in ground state at high π owing to the hydrophobic interaction. The m states consist of a supersaturated solution with aggregates, whereas the s states are suspended microcrystals or micro-oil-droplets with aggregates. The conformations of the molecules in the aggregates were discussed. Single crystal X-ray structure of 2 is reported.     

Synthesis,fluorescence properties,and conformational analysis of ether-linked (1,8)pyrenophanes

Mono-, di- and oligo-ether linked (1,8)pyrenophanes 1–7 were synthesized, and their fluorescence and conformational properties in the absence and presence of metal ions were elucidated. Fluorescence spectra of 1.0 × 10⁻⁵ M solutions of the mono- and di-ether linked pyrenophanes 1–5 were comprised of only monomer emission bands, while those of the oligoethylene glycol linked analogs 6 and 7 contained both monomer and intramolecular excimer emission bands. Addition of perchlorate salts of Ba²⁺, Na⁺ and Li⁺ to 1:1 v/v CH₃CN:CH₂Cl₂ solutions of 6 and 7 caused decreases in the intensities of the corresponding intramolecular excimer emission bands and, in some cases, increases in the intensities of the monomer emission. Monomer and intramolecular excimer emission from the (1,8)pyrenophanes are suggested to arise from the respective anti and syn conformers, whose ratios are dependent on solvent polarity, temperature and kinds of added metal ions.     

Temperature‐induced Molecular Chain Motions of Styrenic Triblock Copolymers Studied by Intrinsic Fluorescence Spectra

The temperature‐induced molecular chain motions of styrenic triblock copolymers (SBC), i.e. polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) and polystyrene‐block‐poly(ethylene‐co‐1‐butene)‐block‐polystyrene (SEBS), were studied by intrinsic fluorescence method. For SBS, the glass transition temperatures (T_gs) of B block and S block obtained by intrinsic fluorescence method were in good agreement with differential scanning calorimetry measurements (DSC). In the case of SEBS, an isoemission point was observed at about 310 nm at elevated temperatures, suggesting the slight conversion between the monomer and excimer emission. On this basis, the molecular chain motion of SEBS was monitored by both fluorescence intensity and excimer/monomer fluorescence ratio. Besides the T_gs of S block and EB blocks, a melting point (T_m) of weak crystalline in EB block was unambiguously determined by intrinsic fluorescence. Furthermore, it was found that the melting process directly led to the slight loosening of PS segments in interface and consequently the reduction of the amount of excimer. A reasonable mechanism was proposed to describe the molecular chain movements and phase transitions of SEBS upon heating. Moreover, the influence of temperature on the apparent activation energy of non‐radiative process (E_a^T) around T_g of S block was much stronger than that around T_g of B or EB blocks.     

CARBOXYLATED ZINC-PHTHALOCYANINE, INFLUENCE OF DIMERIZATION ON THE SPECTROSCOPIC PROPERTIES. AN ABSORPTION, EMISSION, AND THERMAL LENSING STUDY

Monomer and dimer absorption and emission spectra, and dimerization constants are reported for the diamide of the zinc-tetracarboxyphthalocyanine in pure dimethylformamide (DMF) and in H₂O/DMF mixtures at room temperature. The dimerization constant increases steadily with the water content. The monomer absorption Q-band is insensitive to the solvent composition, whereas dimer spectra show great variations with the water content. Stationary emission measurements show that fluorescence originates exclusively from the monomers. The fluorescence spectrum as well as its absolute fluorescence quantum yield, measured by steady-state thermal lensing, are also insensitive to the solvent composition. The thermal lensing method is discussed for the case of two absorbing species in equilibrium.     

聚醚砜激基缔合物的荧光光谱研究

本文研究了劳环在主链上的刚性高分子聚醚砜在二氯甲烷溶液中的荧光光谱.结果表明在适当的浓度下它也能形成分子间激基缔合物.     

Characterization of Chain Motion and Phase Structure of Aromatic Waterborne Polyurethane Film Using Intrinsic Fluorescence Spectra

The phase structure and macromolecular chain motion of aromatic waterborne polyurethane film were examined by the fluorescence technique. Excimer emission of the phenyls appears at 436 and 468 nm and is temperature dependent, suggesting that the hard segments in the intermediate phase can be locally oriented. Binding energy of the excimer structure determined by the intrinsic fluorescence spectra is 16 kJ/mol. The intrinsic fluorescence technique can supply more information than the DSC method on segment relaxations, including α-relaxation for the hard or soft segments, β-relaxation of small molecular units, crystallization of the soft segments, γ-relaxation of the classical consecutive –CH₂– units, and even phase separation degree.     

Self-assembly of a hydrophobically modified naphthalene-labeled poly(acrylic acid) polyelectrolyte in water: organic solvent mixtures followed by steady-state and time-resolved fluorescence

The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes.     

Solvent effect on thermal degradation of plasticized para-substituted polystyrenes

The thermal effect on stability of a series of para-substituted polystyrenes with methyl, methoxy and α-methyl substituents in various solvents was studied in the temperature range of 298-363 K. They gave a monomer fluorescence as a minor part and excimer fluorescence as a major part. Thermal heating of para-substituted polystyrenes shows a decrease in both monomer and excimer fluorescences in all used solvents. Thermal heating causes a small fluorescence quenching effect at lower temperatures in solution but becomes very dominant at higher temperatures. Added terephthalate and phthalate plasticizers to these para-substituted polystyrenes caused a quenching of both monomer and excimer fluorescences without the formation of exciplex emission. The thermal quenching processes of the plasticized polymers were accompanied by a change in the structure of the fluorescence spectra at high heating temperatures. This may indicate that thermodestruction of these polymers starts from a random chain scission. The change in solvent polarity has considerable effect on fluorescence quenching but it has a minor effect on the thermal degradation of these polymers. The binding energies for excimer formation were calculated in the used solvents.     

Novel Ferrocene-Appended β-Ketoimines and Related BF2 Derivatives with Significant Aggregation-Induced Emission and Second-Order Nonlinear Optical Properties

A series of new β-ketoimines containing a ferrocene moiety and their BF₂ complexes have been synthesized and structurally characterized. The solvatochromism of the β-ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β-ketoimines exhibited weak emission, attributable to the excited-state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto-enamine tautomerism, induced upon addition of BF₃ ⋅ OEt₂, which afforded the related BF₂ complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β-ketoimines and BF₂ complexes exhibited significant aggregation-induced emission behavior in mixtures of CH₃CN/H₂O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground- and excited-state dipole moments (μ_g and μ_e), and the origin of electronic absorption spectra were studied by time-dependent DFT calculations. The second-order nonlinear optical (NLO) properties were determined by the electric-field-induced second-harmonic generation technique. The μβ₁₉₀₇ values of the β-ketoimines increased upon the formation of the related BF₂ complexes, mainly due to an enhancement of the ground-state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications.