Photophysics of the analogs of pyrromethene PM 567

The spectral and luminescence properties of a number of pyrromethene (PM) dyes have been investigated. The absorption and luminescence spectra of PM molecules in different solvents are measured. The electronic structure and electronic excited states are calculated by the method of intermediate neglect of differential overlap with special spectroscopic parameterization. The rate constants of photophysical processes are estimated, and the fluorescence quantum yields are calculated. The fluorescence quantum yields of PM I and PM II molecules are found to decrease upon their excitation to the second short-wavelength absorption band. This phenomenon is interpreted.     

N-Triazinyl Derivatives of 1- and 9-aminoanthracene: Synthesis and Photo-Physical Properties

New N-triazinyl derivatives were synthesized by reaction of cyanuric chloride with 1- and 9-aminoanthracenes and subsequent nucleophilic substitution of chlorine atoms on triazinyl ring with methoxy and/or phenylamino groups. The compounds were characterized by ¹H and ¹³C NMR and mass spectra. The influence of the chemical structure and solvent polarity on the UV/Vis absorption and fluorescence spectra and fluorescence quantum yields were investigated. Semi-empirical computations revealed highly polar CT states in singlet excited state manifold connected with charge-transfer from the hydrocarbon moiety to the triazinyl ring. The relationships between the CT-to-emitting state energy gap, solvent polarity and fluorescence quantum yield were discussed.     

铕原子奇宇称高激发态共振电离光谱的研究

采用光电离探测和自电离探测这两种不同的探测方法对铕原子的高激发态光谱进行了详细研究.一方面,采用光电离探测技术,系统测量了在第一电离限之下处于43927—45010 cm^-1能域内的奇宇称能级的光谱.通过光谱定标和误差估算等分析手段,获得了32个共振跃迁峰的位置和强度等光谱信息.并根据所用的激发路线和相关的选择定则等原理,进而确定了这些能级的总角动量. 通过与相关文献资料的对比和分析,研究发现了12个新能级.另一方面,精心设计了一种能够有效识别不同类型高激发态的鉴别方法.对同一能域中 关键词： Eu原子光谱 奇宇称高激发态 孤立实激发（ICE） 自电离探测     

Optical and time-resolved EPR studies of the excited states of azastilbenes and their protonated cations

The effects of protonation on the excited states oftrans-3-styrylpyridine (StP) andtrans-4,4′-dipyridylethylene (DPE) have been studied through measurements of the time-resolved electron paramagnetic resonance (EPR), ultraviolet absorption, and fluorescence spectra in methanol-water mixtures at 77 K. The assignment of the transient EPR signals was carried out with the aid of the stretched poly(vinyl alcohol) films method. From the analysis of these spectra it is concluded that the single protonation appears to have little effect on the zero-field splitting parameters and the anisotropy in the sublevel populating rates of the lowest excited triplet (T₁) states of StP and DPE. However, the decay rate constants of the fluorescent states decrease and fluorescence quantum yields increase on single protonation. These experimental results suggest that the single protonation causes a decrease in the intersystem crossing (ISC) rates for the three T₁ sublevels. These results are explained in terms of the vibronic mixing between the¹nπ* and¹ππ* states in the lowest excited singlet state. The assignment of StP to the specified conformer was carried out through the analysis of the anisotropic ISC processes.     

Structure and Luminescent Properties of the 4-Arylidene-2-Aryl-5-Oxazolones(Azlactones)In Solution and Crystalline State

Experimental and theoretical evaluations have proven that very low fluorescence quantum yields of azlactones in solution are not caused by an efficient inter system crossing from S₁*(ππ) to T*(nπ) states, but rather from solvation and steric effects, that result in non-planarity of the molecular system. High fluorescence quantum yields in the solid state are attributed to the planarity of the azlactone molecule upon packing into the crystal lattice. Supporting evidence was found upon observation of the excited state proton transfer (ESIPT) bands of fluorescence emissions of o-hydroxyarylidene derivatives. The photoinstability of azlactones in liquid states are attributed to photochemical E-Z isomerization and cleavage of the hetero ring α to the carbonyl group.     

Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance

We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state.     

Electronic states of the CeO molecule: Absorption,emission, and laser spectroscopy

The electronic spectrum of the CeO molecule is characterized by the existence of many 0-0 bands resulting from transitions between various Ω components of excited states and the 16 lower Ω states which arise from the lowest configuration… (4f)(6s). Classical studies of rotational structure of absorption and emission spectra have been extended, and argon-ion and tunable dye (coumarin 460, rhodamine 6G, rhodamine 101) lasers have been used to excite known transitions in bands which had previously been rotationally analyzed. The resulting fluorescence spectra have been used to establish the relative energies of the lower states. By tuning the lasers to excite analyzed transitions from different known electronic states it has been possible to determine the energies of 16 low-lying states, to assign quantum numbers to 14 with certainty, and to suggest assignments for the other 2. The resulting energy level diagram of lower states is discussed and shown to correlate well with the 4f6s configuration of the Ce²⁺ ion. From the energies of the low-lying states, those of the higher excited states are calculated and in some cases new values of vibrational and rotational constants are derived.     

Fluorescence Dynamics of Three UV-B Sunscreens

Polarity of the surrounding medium affects the excited states of UV-B sunscreens. Therefore understanding excited state processes in a mixed polarity model system similar to skin is essential. We report the excited state lifetimes, quantum yields, radiative and non-radiative rates of three sunscreens. Among the three UV-B sunscreens studied, octyl salicylate emits from a single excited state, while padimate O and octyl methoxy cinnamate show multiple states. The radiative rates of salicylate and cinnamate are approximately constant, while that of padimate O depends strongly on solvent. The non-radiative rates of all sunscreens vary with solvent polarity. Compared to salicylate and cinnamate, padimate O is complex to analyze because of its two emission peaks and one peak’s strong dependence on the dielectric constant. High absorbance, broad absorption peak with small fluorescence quantum yield, and low radiative rate make octyl methoxy cinnamate a superior UV-B sunscreen ingredient. The complexity in excited-state analysis shows that the lifetimes of the sunscreens are critical parameters, in addition to absorbance and quantum yield. Fluorescence lifetime substantiates the use of polystyrene nanospheres as a model host to study the photo-physical properties of sunscreen in a heterogeneous environment.     

Spectroscopy of highly luminescent 1,3,5-triazapentadiene complexes of platinum(II) in solution and in the adsorbed and solid states and quantum-chemical interpretation

We have measured the absorption, luminescence, and luminescence excitation spectra, as well as the excited-state lifetimes and luminescence quantum yields, of 1,3,5-triazapentadiene complexes of platinum(II) in a solution, in the solid state, in an adsorbed state on a SiO₂ surface, and in a polystyrene matrix at room temperature and at 77 K. We also have performed quantum-chemical calculations of the equilibrium geometry of the ground and excited states of the complexes and of the nature and structure of molecular orbitals.     

The E.S.R. and electronic absorption spectra of Chichibabin's biradical

The absorption spectra of a number of saturated hydrocarbons in the vacuum ultra-violet region have been examined and compared with their photoelectron and electron-loss spectra. Important conclusions about the quantum defect associated with the excited electrons and the nature of the excited states have been drawn from the relative positions of these spectra. The Rydberg bands of ethane, which were initially thought to originate in the C-C bond, have been shown to be associated with an electron largely localized in the CH₃ group.     

Using two-dimensional photon echo spectroscopy to probe the fine structure of the ground state biexciton of CdSe nanocrystals

The origin of the fine structure of the ground state single- and biexciton of CdSe nanocrystals is reviewed, along with the theoretical framework used to describe these states. Calculations were performed to determine the transition dipole moments of optically allowed transitions from the single- to biexciton fine structure states. Two-dimensional photon echo spectroscopy measurements for a sample of CdSe nanocrystals are reported. The two-dimensional electronic spectrum at a population time of 0 fs is analyzed using a simulation based on k.p theory predictions of the exciton and biexciton manifolds of states. The analysis suggests that a particular excited state absorption transition from the single- to biexciton fine structure dominates the 2D spectra. These excited state absorptions are clearly resolved in 2D spectra and the method therefore has promise for gaining clearer insights into quantum dot spectroscopy.     

不同取代基对喹啉电子光谱影响的理论研究

不同取代基团会引起电子光谱发生不同的变化,为获得分子结构与电子光谱之间的关系,采用量子化学计算方法进行了理论分析。使用DFT、CIS分别对基态、激发态进行几何结构优化,再用TDDFT计算优化结果得出电子光谱。结果表明:不同取代基团都改变了碳氮环基态、激发态的几何构型,前线区域轨道能量,π电子共轭系统,这些变化都导致电子光谱发生相应变化。得出不同取代基对电子光谱的影响规律,为电子光谱分析鉴定衍生物提供了理论参考。     

A combined theoretical and experimental study on molecular photonics

A detailed account of quantum chemical procedures for estimating the rate constants of the photophysical processes at work in polyatomic organic molecules is given. The results obtained from combined experimental and theoretical research into the spectral-luminescent properties of acridine, 9-aminoacridine, 2,7-dimethyl-9-diphenylaminoacridine, and of their protonated forms are reported. The electronic absorption and fluorescence spectra of acridine have been investigated at room temperature in ethanol solution of varying pH and in other solvents of different chemical nature and polarity. The energy of excited states, the rate constants of the deactivation of the excited states, and the dipole moments obtained by quantum chemical methods for the examined compounds are presented. The findings of the investigations are discussed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 93–107, October, 2008.     

Excited state quantum phase transitions in many-body systems

Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean-field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions.     

Measurement of the Wigner Characteristic Function for the Center-of-Mass Motion of Two Trapped Ions

We proposed a scheme for the reconstruction of the quantum states for the center-of-mass vibrationalmode of two trapped ions. In the scheme the ions are multichromatically excited by three lasers. Then measurementof the difference between probabilities of the ions being both in electronic ground and excited states directly yields theWigner characteristic function for the center-of-mass vibrational state. The scheme can also be used to prepare entangledcoherent states for the center-of-mass and relative vibrational modes.     

Measurement of the Wigner Characteristic Function for the Center－of－Mass Motion of Two Trapped Ions

We proposed a scheme for the reconstruction of the quantum states for the center-of-mass vibrational mode of two trapped ions. In the scheme the ions are multichromatically excited by three lasers. Then measurement of the difference between probabilities of the ions being both in electronic ground and excited states directly yields the Wigner characteristic function for the center-of-mass vibrational state. The scheme can also be used to prepare entangled coherent states for the center-of-mass and relative vibrational modes.     

Energy levels of the Fröhlich polaron in a spherical quantum dot

The one-phonon variational state is suitably applied to describe the ground state and excited states of the Fröhlich polaron bound to a quantum dot. A general analytical expression for the electronic energy spectra and the polaron binding energy for different electronic subband bound states in a quantum dot is presented and discussed with reference to the parameters of a real solid.     

Eu原子4f~76snlRydberg态的研究

利用三步双色共振激发技术和三步三色孤立实激发技术,系统地研究了铕原子在42250—44510 cm~(-1)能域内的光谱特性,提供了该能域内56个束缚高激发态的光谱信息.为了能确定这些态的光谱归属,进行了两方面的探索:第一,观察能否利用孤立实激发技术,把处于这些态上的铕原子进一步共振激发到自电离态,从而推断这些态属于单电子激发的束缚Rydberg态还是属于双电子激发的价态,并对Rydberg态的电子组态进行了光谱确认;第二,通过计算这些态相对于各个电离阈的量子亏损并观察它们分别收敛于哪个电离阈,以便获取其主量子数的信息.最后,设计并采用了三种不同的激发路径,分别将原子布居到同一高激发能域并探测它们在该能域的光电离光谱.通过比较这些光谱的异同并结合上述激发路径所对应的跃迁选择定则,便可惟一地确定这些高激发态的总角动量.研究发现:所探测到的高激发束缚态只有三个属于单电子激发的束缚Rydberg态,其余都是价态.本文确定了这三个Rydberg态的电子组态和原子状态.     

Resonant Raman scattering spectra in a ZnCdSe/ZnSe structure with a quantum well and open nanowires

Resonance Raman scattering (RS) spectra of a ZnCdSe/ZnSe sample containing a single quantum well and quantum well-based open nanowires were studied at T=300 K. The longitudinal optical (LO) phonons involved in the formation of the observed spectra of the quantum-well and nanowire regions differ noticeably in energy. The LO phonon energies in the structures under study were calculated taking into account the compositional effect (doping of Cd into ZnSe) and biaxial strain. When excited in the exciton resonance region, RS is shown to occur via free (extended) excitonic states with the involvement of LO phonons of the ZnCdSe strained layer with final wave vectors near the Brillouin zone center. When excited below the excitonic resonance in the ZnCdSe layer, resonance scattering via localized exciton states provides a noticeable contribution to the observed RS lines. Because of the finite size of a localized state, phonons with large wave vectors are involved in these scattering processes. The RS lines produced under excitation in the excitonic region of the thick barrier layers are due to scattering from the ZnSe barrier phonons.