Strong coupling in macrocyclic thiophene investigated by time-resolved two-photon excited fluorescence

We report the femtosecond dynamics of fluorescence anisotropy excited through the two-photon absorption (TPA), which provides direct signatures of delocalized electronic excitations for symmetrical macromolecular architectures. Two-photon excited fluorescence anisotropy is strongly correlated with the orientation and value of the transition moment from the excited state to the second and higher lying states. For macromolecular systems it leads to a relatively low initial fluorescence anisotropy and specific femtosecond anisotropy dynamics. We have experimentally demonstrated qualitatively different anisotropy dynamics for two- and one-photon absorption excitations for strongly coupled ring architecture prospective for artificial-light-harvesting applications and possessing an enhanced TPA-absorption cross section.     

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     

Extended Förster theory of donor-donor energy migration in bifluorophoric macromolecules. Part I. A new approach to quantitative analyses of the time-resolved fluorescence anisotropy

The applicability of an extended Förster theory (EFT) is explored with respect to donor-donor energy migration within a pair of identical fluorophores. The EFT accounts for reorienting motions and orientational restrictions of donor groups, which are attached to a macromolecule. Because EFT involves averaging over stochastic functions, it is inappropriate for the conventional methods used for analysing fluorescence depolarization experiments. For this reason approximations of the EFT were derived. To examine the validity of these different approximations, depolarization data were generated and re-analysed. To create the depolarization data, the EFT was used together with a Brownian dynamics simulation. Limitations of the approximate EFT are ascribed to the handling of secondarily excited donors (i.e. donors excited through energy migration). Finally on the basis of the EFT, a simulation-deconvolution method is presented which enables one to analyse the fluorescence anisotropy, without introducing any approximation.     

Monte-Carlo Simulation of Energy Migration in Uniaxially Oriented Polymer Films

Nonradiative electronic energy migration between identical fluorophores is studied numerically in uniaxially oriented polymer films. The reorientation effect of dipole moments induced by film stretching leads to extremely different concentration- and time-courses of emission anisotropy compared to those in disordered system. In particular, the effect of a much weaker concentration depolarization of fluorescence is due to the fact that not only primarily excited molecules contribute to emission anisotropy in oriented films.     

乙醇-水团簇分子形成激基缔合物及荧光发射机理研究

紫外光照射具有特殊结构的长链式乙醇-水团簇分子时,处于激发态和基态的分子形成了分子间激基缔合物,并发射荧光.根据实验结果分析和能量转移理论可知,激发态单分子和激基缔合物间形成了电子迁移洛合物并发生了能量转移.根据Mulliken理论对电子迁移洛合物进行量子力学处理,得出了团簇分子在基态和激发态能量E^b_N和E^b_E以及由于电子迁移而引起的静电相互作用能E^s;根 关键词： 荧光光谱 激基缔合物 电子迁移 乙醇-水团簇     

Spectral properties of several fluorene derivatives with potential as two-photon fluorescent dyes

Investigations of the absorption, steady-state fluorescence, excitation and excitation anisotropy properties of several fluorene derivatives, (7-benzothiazol-2-yl-9,9-didecylfluoren-2-yl)-diphenylamine, 9,9-didecyl-2,7-bis-(N,N-diphenylamino)fluorene and {4-[2-(7-diphenylamino-9,9-diethylfluoren-2-yl)vinyl]phenyl}phosphoric acid diethyl ester, in liquid solutions have been conducted. Spectral characteristics of these compounds, including fluorescence quantum yields, were measured in acetonitrile, methylene chloride, tetrahydrofuran and hexane at room temperature. Excitation anisotropy spectra provided a means to determine the nature of the short wavelength absorption bands as an electronic transition into a higher excited singlet state. It was found that excitation spectra in the short wavelength region do not correspond to the absorption bands that are correlated with the wavelength dependence of the fluorescence quantum yields. Major reasons of such spectral behavior are discussed.     

The effect of lead cations on the fluorescence characteristics of bovine serum albumin in aqueous solution

The effect of lead (heavy metal) cations on the fluorescence characteristics and photophysical parameters (fluorescence intensity and anisotropy, absorption cross section, excited state lifetime, and rates of singlet-triplet conversion and reversible photobleaching) of tryptophan in an aqueous solution of bovine serum albumin (two-tryptophan protein) is studied and compared with the effect in the aqueous solution of tryptophan. It is demonstrated that the effect of lead on the fluorescence characteristics of the protein is manifested at a molar concentration ratio of metal cations and protein macromolecules of greater than 10 and related to the dynamic quenching of the excited state, protein aggregation, and an increase in the rate of singlet-triplet conversion (the effect of a heavy atom) in tryptophan molecules.     

Fluorescence quenching as a method of identification of the character of photoreactions in excited states of molecules

We consider the steady-state monochromatic excitation of a luminophore that has fluorescent products. We consider how the fluorescence of singlet states is affected by different means of quenching highlying excited states such as quenching with impurities, temperature quenching, and shortening the lifetime with induced transitions in the light field. We show that the use of different methods of fluorescence quenching opens new possibilities for studying photoreactions that proceed via excited singlet states. Our consideration concerns a wide range of primary photoprocesses, such as electron density redistribution (internal electron transfer) in the excited state, protolytic reactions, intramolecular proton transfer (phototautomerization), hydrogen bond formation, intermolecular relaxation of molecules in solutions, and formation of excimers and exciplexes. The obtained relations have been used to analyze experimental fluorescence spectra of solutions of some organic compounds, including derivatives of 3-hydroxyflavone and 3-aminophthalimide, subjected to quenching by different methods.     

Continuous Fluorescence Depletion Anisotropy Measurement of Protein Rotation

Protein rotation in viscous environments can be measured by fluorescence depletion anisotropy (FDA) which combines long lifetimes of chromophore triplet states with the sensitivity of fluorescence excitation and detection. FDA achieves sensitivity well beyond that attainable by the more common technique of time-resolved phosphorescence anisotropy (TPA). We have now combined benefits of both time-domain and frequency-domain FDA into a single continuous technique (CFDA). Intensity and polarization of a single laser beam are modulated continuously according to a complex, repeating waveform. Fluorescence signals excited from triplet-forming fluorescent probes are digitized over recurring waveform periods by a high-speed signal averager. CFDA experiments typically involve substantial ground state depletion. Thus signals, unlike those of TPA, are not linear in the exciting light intensity and simple data analysis based on such linearity is not appropriate. An exact solution of the coupled diffusion and triplet production/decay equation describing CFDA within individual data points has been combined with simulated annealing optimization to extract triplet and anisotropy decay kinetics from experimental data. Related calculations compare possible excitation waveforms with respect to rotational information provided per fluorescence photon. We present CFDA results for the model system of eosin conjugates of carbonic anhydrase, BSA and immunoglobulin G in 90% glycerol at various temperatures and initial cellular results on eosin-IgE bound to 2H3 cell Type I Fcε receptors. We explore how CFDA reflects rotational parameters of heterogeneous systems and discuss challenges of extending this method to single cell microscopic measurements.     

水杨醛缩对乙酰基苯胺希夫碱的合成及其荧光性质的理论研究

以水杨醛和对乙酰基苯胺为原料,首次采用绿色环保的室温固相反应方法制备了水杨醛缩对乙酰基苯胺希夫碱,用元素分析和核磁共振氢谱对产物进行了表征。测定了产物的紫外光谱、荧光光谱和相对荧光量子效率,发现该化合物具有较强的荧光性质。利用密度泛函理论(density functional theory, DFT)方法,在B3LYP/6-311G基组水平上优化了该化合物的基态分子构型。采用相同的方法和基组计算了标题化合物的振动频率,频率数据中没有虚频,即该优化构型是稳定的。分析理论计算结果发现：标题分子具有较强的芳香性和较大共轭体系。在基态优化结构的基础上应用含时密度泛函理论(TD-DFT),在B3LYP/6-31G水平上计算并研究了此化合物的吸收光谱。用单激发组态相互作用(CIS)方法优化了标题分子的激发态构型,并在此基础上用TD-DFT//B3LYP/6-31G方法计算了这种化合物的荧光发射光谱。将理论计算的光谱性质与实验的光谱数据相比较发现二者吻合较好。分析探讨了化合物分子的结构与其荧光性质之间的关系,为进一步寻找具有荧光性质的化合物提供了理论指导。     

Ag8 fluorescence in argon

The fluorescence of Ag8 in an argon matrix and in argon droplets is reported. This is the first unambiguous assignment of the fluorescence of a metal cluster larger than the tetramer, indicating that the excited state lifetime is longer than previously thought. It is discussed as a possible result of a matrix cage effect. The excitation spectrum is compared with two-photon-ionization measurements of Ag8 in helium droplets and to known absorption data. The agreement is excellent. We propose that the excited states relax rapidly through vibrational coupling to a long-lived state, from which the fluorescence occurs.     

MOLECULAR STRUCTURE AND PHOTOPHYSICS OF N-QUATERNARY DIARYLOXAZOLIUM SALTS

ABSTRACT

The concern of this work is to study molecular structure, electronic absorption and emission spectra of several N-quaternary salts of the well-known diaryloxazole scintillating compounds: 2,5-diphenyloxazole, para-, meta- and ortho- isomers of bis-2-(5-phenyl-oxazolyl)-benzene (POPOP). All of them were obtained from the initial aryloxazoles by their methylation with dimethylsulfate.

We found, that N-methylation manifests itself in arising of sterical hindrance in the molecules of diaryloxazolium salts, which results in distortion of their planarity. On the contrary to the ground state, the investigated molecules become more planar in their lowest singlet excited state. As a result of such an excited state flattening, fluorescence Stokes shifts values of the diaryloxazolium salts exceed 9000–10,000 cm^?1. The excited state flattening rate constants, estimated for the studied oxazolium compounds, are of the 10¹⁰ s^?1 range. No considerable increase of radiationless losses, induced by the excited state structural relaxation, was found. Owing to these facts, N-quaternary diaryloxazolium salts may be considered as effective abnormally high Stokes shift organic luminophores.     

碳碳双键共轭分子在玻璃态形成一个新的体积保守的扭转辐射态

采用时间分辨的单光子计数技术和TDDFT计算方法研究了激发态HY103分子的特性. 在室温下溶液中HY103分子被光激发后会发生光诱导的沿双键旋转的异构化,导致了HY103分子非常短的荧光辐射寿命和较弱的荧光辐射强度. 当HY103分子在77 K的玻璃态被光激发后,HY103分子的正常荧光辐射寿命被延长至2 ns左右,而且荧光辐射的强度也得到增强. 此外还观察到了一个新的辐射态和具有的性质. 这不仅能够诱导碳碳双键的共轭分子在空间束缚的环境中发生光致异构化,也可以形成一个新的稳定的辐射态.     

Anisotropic x-ray emission from heliumlike Fe24+ ions aligned by resonant coherent excitation with a periodic crystal potential

We have measured deexcitation x rays emitted from the resonant coherently excited 2(1)P(1) state of heliumlike Fe24+ ions of 423 MeV/amu, planar channeling through a Si crystal. Large anisotropy in the angular distribution of deexcitation x-ray emission is observed: the x-ray emission in the direction parallel to the channeling plane is favored by a factor of 2 compared to the perpendicular direction. This anisotropy originates from the direction of the periodic crystal field, which populates specific m states in resonant coherent excitation and aligns the excited states.     

Tuning the Solution Phase Photophysics of Two De Novo Designed Hydrogen Bond Sensitive 9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one Derivatives

Two new fluorophores, 6,7-dimethoxy-9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (DMTCO) and 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO), first of their kind, have been synthesized from the corresponding methoxy and methylenedioxy derivatives of 2,3,4,9-tetrahydro-1H-carbazol-1-one respectively. Comprehensive photophysical characterization of these compounds has been carried out in sixteen different homogeneous solvents and binary solvent mixtures. Both of these compounds are sensitive to solvent polarity, but the sensitivity is much higher in electronic excited state observed by steady-state and time-resolved fluorescence experiments than in ground state studied by UV–vis absorption spectroscopy. The fluorescence spectral shifts are linearly correlated with the empirical parameters of the protic solvents and also the quantitative influence of the empirical solvent parameters on the emission maxima of the compounds has been calculated. The change in dipole moment of the compounds in their excited state has been calculated from the shifts in corresponding emission maxima in pure solvents. A higher dipole moment change of both DMTCO and MDDCO in protic solvents is due to intermolecular hydrogen bonding which is further confirmed by the comparison of their behaviour in toluene-acetonitrile and toluene-methanol solvent mixtures. From structural features, MDDCO is more planar compared to DMTCO, which is reflected better in fluorescence quenching of the former with organic bases, N,N-dimethylaniline and N,N-diethylaniline. Laser flash photolysis experiments prove that the quenching interaction originates from photoinduced electron transfer from the bases to the compounds.     

TDDFT Calculations of Electronic Spectra of Benzoxazoles Undergoing Excited State Proton Transfer

Energies and oscillator strengths of vertical transitions for various rotameric and tautomeric species of 2-(2′-hydroxyphenyl)benzoxazole (HBO), 2,5-bis(2-benzoxazolyl)phenol (DBP) and 2,5-bis(2-benzoxazolyl)hydroquinone (BBHQ) have been calculated in the ground and first excited states with the use of TDDFT methods. The TDDFT results demonstrate good correspondence to the frequencies of absorption and fluorescence bands of the benzoxazoles reported for measurements in supersonic jets and solution, but fail to predict relative energies of the enol and keto tautomers of DBP and BBHQ in the excited state. Low intensity of the fluorescence bands attributed to the conformations of HBO and DBP that do not undergo excited state proton transfer is shown to be caused by low concentrations of the conformations in the ground state. For the three compounds large-amplitude twisting of the keto tautomer is found to be one of radiationless processes resulting in decrease of the fluorescence with a large Stokes shift.     

l-Dityrosine: A time-resolved fluorescence investigation

We have investigated the time-resolved fluorescence properties ofll-dityrosine in aqueous solution. Typically, three exponential components were needed to fit the fluorescence pattern adequately, with pure decay terms for the low-intensity, high-energy state (_em = nm) but with a pronounced subnanosecond rise phase for the predominant red-edge fluorescence (_em > 380). Dual fluorescence behavior is indicative of an intramolecular precursorsuccessor pair, i.e., a consecutive intramolecular excited-state reaction. We suggest that this reaction is a torsional motion of the (deprotonated) monoanion along the biphenolic bond. Analysis of the fluorescence anisotropy decay of dityrosine yielded two rotational correlation times, the longer of which is associated with a negative preexponential term. The increase with time in the horizontally polarized component of the intensity decay is interpreted as the result of an electronic rearrangement in the excited state when the successor form of dityrosine is generated. Lifetime distributions of experimental data were probed by an unbiased exponential series method which uses a Tikhonov-type regularization function. The procedure revealed three well-separated groups of lifetimes, the short-lived ensemble forming a formally negative distribution. A photophysical model is introduced which interprets the biexponential decay of dityrosine in terms of overlapping emission signals from the precursor and the successor molecule.     

Excited State Absorption Study in Hematoporphyrin IX

We present the study of the excited state absorption of Hematoporphyrin IX dissolved in dimethyl sulfoxide. All measurements were carried out using open aperture Z-scan and white-light continuum pump-probe with picosecond pulses to avoid triplet excited state absorption. Without the latter contribution, the results obtained with both techniques show a transition to a high singlet excited state. The vibronic progression of the Q-band is observed due to photobleaching of the ground state. In addition, we show that the excited state presents reverse saturable absorption for most of the spectral range studied. A long relaxation component of the first singlet excited state was evidenced with the pump-probe experiment. This result is in agreement with fluorescence lifetime and fluorescence quantum yield measurements. In order to elucidate the origin of the nonlinear effects, we used a three-level energy diagram to describe the principal singlet-singlet transitions.     

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。     

State reconstruction of a qutrit by a minimal set of discrete measurements

We propose a simple and practical method for measuring the parameters of a fully or partially coherent superposition state of a qutrit quantum system. The method is based on the coupling of the qutrit to an excited state by two polarized laser fields and measurement of the fluorescence or ionization signal from the excited state for a discrete set of laser ellipticities and phases. We show that nine independent signals suffice to determine the parameters of an arbitrary unknown mixed qutrit state.