Kinetics of the fluorescence of poly(N-vinylcarbazole) and poly(N-vinylcarbazole) with 2,4,7-trinitrofluorenone in the solid state

The fluorescence decay time measurements by the stroboscopic method have been made on films of amorphous poly(N-vinylcarbazole) (PVCA) and PVCA doped with 2,4,7-trinitrofluorenone (TNF). The obtained lifetimes of two excimer species have at 77 K and at 300 K values of about 43 ns and 9 ns, which are similar to other measurements. The kinetics of excimer fluorescence and energy transfer in PVCA films are described by a simple model of the Stern-Volmer type. It assumes the fast migration of localized singlet excitons and their trapping in two species of excimer traps.We propose a modified kinetic model for films of PVCA with TNF. In this model we assume besides the exciton migration and trapping on excimer and impurity traps also the direct energy transfer from two excimer species to charge transfer complexes of PVCA with TNF by the Förster dipole-dipole mechanism. The estimated critical distance of this transfer are about 10 Å.     

人工模拟捕光天线分子中超快能量转移的瞬态荧光测量

利用飞秒时间分辨瞬态荧光光谱仪测量苝四甲酰二亚胺三聚体内的超快荧光淬灭过程. 观察到因能量转移而导致的单体荧光的快速衰减,这一过程的时间常数约为0.82 ps.     

Steady state and time-resolved studies of pyrene in solution and in single microcrystals

Single microcrystals of pyrene have been studied by steady state and time resolved fluorescence microscopy. The fluorescence spectra of microcrystals exhibit vibrational structure unlike the broad spectrum observed in pyrene excimer. A risetime is observed in the decay curves of the concentrated solutions, indicating the excimer formation. In contrast, the fluorescence decay profiles of the single microcrystals are nonexponential in nature and the decay times vary with their size and the wavelength of emission. This behaviour has been explained mainly by considering the pyrene dimer stabilized in the ground state.     

基于有机染料盐掺杂薄膜体系的能量转移及光致发光特性研究

利用稳态和时间分辨瞬态光谱研究了有机盐trans-4-［p-(N-ethyl-N-(hydroxyethyl)amino)phenylstyryl］-N-(hydroxyethyl)pyridinium iodide (ASPI)掺杂聚合物PVK(聚乙烯咔唑)薄膜体系的光致发光和能量转移特性. 在ASPI：PVK掺杂薄膜体系中,PVK的荧光强度与寿命随掺杂浓度的升高而降低,表明两者存在有效的Forster能量转移. 通过在相对低浓度的掺杂体系中加入适量高量子效率的Alq3作为能量转移过渡体,形成能量转移级 关键词： 有机染料盐 荧光光谱 荧光寿命 能量转移     

Fluorescence quenching of dye molecules near gold nanoparticles: radiative and nonradiative effects

The radiative and nonradiative decay rates of lissamine dye molecules, chemically attached to differently sized gold nanoparticles, are investigated by means of time-resolved fluorescence experiments. A pronounced fluorescence quenching is observed already for the smallest nanoparticles of 1 nm radius. The quenching is caused not only by an increased nonradiative rate but, equally important, by a drastic decrease in the dye's radiative rate. Assuming resonant energy transfer to be responsible for the nonradiative decay channel, we compare our experimental findings with theoretical results derived from the Gersten-Nitzan model.     

Excimer emission from evaporated pyrene films

Emission spectra and decay times of fluorescence of pyrene thin films prepared by evaporation onto glass substrate at low temperatures were measured. The band positions of the excimer emission from the films evaporated onto substrates at temperatures below about 200 K, are found to the lower energy side of those of the crystal. The decay time of excimer emission in a film prepared by evaporation onto a substrate cooled with liquid nitrogen is about 100 ns at 85 K and is shorter than that of the crystal. These results are discussed in relation to an amorphous structure in the pyrene evaporated thin films. The energy transfer was also studied in evaporated pyrene films containing perylene as a dopant. The results are explained in terms of excimer exciton diffusion through the crystalline structure in the film.     

Dimensional dependence of the energy transfer in MBE grown MnS layers

MBE grown MnS layers with different thicknesses have been studied by time resolved photoluminescence spectroscopy. The temporal evolution of the internal Mn²⁺ (3d⁵) luminescence is measured over 3 orders of magnitude in intensity. The decay curves obtained reveal a surprising but distinct dependence on the layer thickness with longer lifetime than thinner layers. The observed non-exponential behavior of those time transients can be well described by an energy diffusion model within the 3d states of the manganese subsystem and a subsequent dipole–dipole energy transfer to radiationless centers.     

聚乙烯基咔唑与Alq3混合薄膜的发光性能与能量传递过程

研究了Alq3与聚乙烯基咔唑(PVK)按不同比例的混合体系制备的薄膜的发光特性.通过对混合薄膜的吸收光谱、激发光谱和发射光谱的分析，研究了PVK与Alq3之间的 能量传递规律.当Alq3与PVK的质量比为1∶7时，能量传递效率最高.用一个由单链模 型扩展到包括杂质的哈密顿量对实验进行模拟，发现该模型能够较好地解释有关的实验结果. 关键词： 吸收光谱 激发光谱 发射光谱 能量传递     

Electronic spectroscopy of highly-polar aromatics. V. The polar excimer of N,N-dialkyl-p-cyanoaniline

The fluorescence spectra of N, N-dialkyl-p-cyanoanilines in fluid media have been re-examined. The long-wavelength fluorescence, previously attributed to a solvated ¹L_a → ¹A₁ fluorescence, is interpreted as an excimer fluorescence, an assignment which is supported by concentration dependence studies and quenching experiments. The temperature dependence of the excimer/ monomer fluorescence intensity ratio indicates that excimer formation is a diffusion controlled process. The binding energy of the excimer is found to be independent of the nature of the solvent and to be smaller than those values estimated for excimers of polycyclic aromatic hydrocarbons. Solvent viscosity, solvent polarity and specific solvent-solute interactions affect the excimer/monomer fluorescence intensity and these effects are interpreted. The geometry of the excimer is also discussed.     

Migration of excimers in pyrene crystals

Emission decay times of the new excimer were measured for undoped and perylene doped pyrene crystals. From the decay times obtained, the temperature dependence of the diffusion coefficient of the excimers was deduced by assuming a model in which two electronic states of the new excimer are involved in the energy transfer process. Within this model, it was found that in the upper excimer state the excimers migrated by a hopping process, while in the lower excimer state they migrated as free excimer excitons while undergoing phonon scattering.     

DCM掺杂PVK体系的超快光谱

利用稳态荧光光谱和时间分辨超快光谱研究了DCM掺杂PVK(聚乙烯咔唑)体系的发光特性和能量转移。根据DCM的吸收光谱与PVK的荧光光谱,用Frster理论估算出DCM:PVK掺杂体系能量转移的临界半径及其效率。在DCM:PVK掺杂薄膜中,随着掺杂浓度的升高,DCM的发射强度增强,PVK的发射强度减弱,两者相对强度之比与估算结果一致。还利用时间分辨超快光谱研究了DCM:PVK掺杂薄膜体系的能量转移动力学过程,观察到DCM:PVK掺杂薄膜的荧光寿命随着掺杂浓度的升高逐渐变短。结果表明,在DCM:PVK掺杂薄膜中,存在从PVK到DCM较为有效的Frster能量转移。     

Photoinduced interaction between MPA capped CdTe QDs and certain anthraquinone dyes

Photoinduced interaction of mercapto propionic acid (MPA) capped CdTe quantum dots (QDs) with certain anthraquinone dyes namely alizarin, alizarin red S, acid blue 129 and uniblue has been studied by steady state and time resolved fluorescence measurements. Addition of anthraquinone dyes to CdTe QDs results in the reduction of electron hole recombination has been observed (i.e., fluorescence quenching). The Stern-Volmer constant (K_SV), quenching rate constant (k_q) and association constants (K) were obtained from fluorescence quenching data. The interaction of anthraquinone dyes with QDs occurs through static quenching was confirmed by unaltered fluorescence lifetime. The occurrence of electron transfer quenching mechanism has been proved by the negative free energy change (ΔG_et) obtained as per the Rehm-Weller equation.     

四苯基卟吩激发—重态衰变的“外部重原子效应”的研究

考查了在有芳烃卤代物RX(如氯苯、溴苯和碘苯)存在时,四苯基卟吩TPP的荧光衰变现象。基于荧光衰变动力学分析,发现:在RX和TPP之间生成复合物是引起重原子效应的一个基本步骤。荧光衰变的动力学参数则进一步表明:可观察的外部重原子效应主要是由于发生分子间电荷转移相互作用而引起的。     

凝聚相有机分子的激发能传递研究(Ⅱ)——激光染料二甲基-POPOP和DCM分子间的激发能传递

利用荧光发射及其衰变动力学测量,研究了激光染料分子二甲基-POPOP和DCM在溶液中的分子间能量传递。所得结果证实:激发态二甲基-POPOP分子荧光被猝灭的程度,随所加入DCM浓度的增大而增大。尽管DCM的荧光寿命随二甲基-POPOP的猝灭而增加。然而,DCM的加入并不改变二甲基-POPOP的荧光寿命。在固定DCM浓度,而增加二甲基-POPOP浓度时,相似的结果同样被观测到。这些结果表明:激发态二甲基-POPOP分子通过辐射传能机理向基态DCM传递激发能,其结果将入射光的波长从紫外直接转换到波长大于600nm的光谱区。在本文中也简要讨论了进一步改善这一传能过程效率的措施。     

荧光光谱法研究亚甲基蓝与蛋白质的结合反应

应用荧光光谱法研究了水溶液中亚甲基蓝与牛血清白蛋白分子间的结合反应 ,讨论了亚甲基蓝对蛋白质内源荧光的猝灭机理 ,测定了结合常数 (KA=3 44× 10 5L·mol-1)和结合位点数 (n =1 0 3)。依据F rster非辐射能量转移 ,理论确定了授体 受体间的结合距离 (r=1 6 7nm)和能量转移效率 ,并用同步荧光技术考察了亚甲基蓝对牛血清白蛋白构象的影响     

伊文思蓝与牛血清白蛋白相互作用的研究

利用荧光光谱和紫外吸收光谱研究了伊文思蓝（Evans blue,EB）与牛血清白蛋白（Bovine serum albumin,BSA）的相互作用。伊文思蓝与牛血清白蛋白作用,使牛血清白蛋白的荧光发生猝灭,利用Stern-Volmer方程和荧光寿命的测定,确定了伊文思蓝对牛血清白蛋白的荧光猝灭为静态猝灭和非辐射能量转移。实验测得伊文思蓝与牛血清白蛋白的结合常数KBSA-EB为1.122×106L·mol-1,结合点数n为0.994;根据Foerster非辐射能量转移理论,得到伊文思蓝与牛血清白蛋白之间的能量转移效率E为0.276,作用距离r为3.14nm。同时,利用同步荧光光谱研究了牛血清白蛋白的构象变化。     

掺杂PVK薄膜的荧光谱及电荷转移

根据PVK掺杂后荧光谱的变化，说明掺杂PVK薄膜的电致发光存在着从基质分子向掺杂分子的能量传递，用一个由单链模型扩展到包括杂质的哈密顿量进行数值求解，结果表明：在PVK和杂质分子之间有效的能量传递是源于它僮之间的电荷转移，且随着杂质浓度的变化，其荧光谱峰位的移动与掺杂前后系统总能量的改变及荧光谱强度与掺杂后转移的电荷数之间分别存在对应关系。该模型较好地解释了有关的实验结果。     

Single molecule spectroscopy on photosynthetic pigment-protein complexes

Single molecule spectroscopy was applied to unravel the energy transfer pathway in photosynthetic pigment-protein complexes. Detailed analysis of excitation and fluorescence emission spectra has been made for peripheral plant antenna LHC II and Photosystem I from cyanobacterium Synechococcus elongatus. Optical transitions of individual pigments were resolved under nonselective excitation of antenna chlorophylls. High-resolution fluorescence spectroscopy of individual plant antenna LHC II indicates that at low temperatures, the excitation energy is localized on the red-most Chl a pool absorbing at 680 nm. More than one pigment molecule is responsible for the fluorescence emission of the LHC II trimer. The spectral lines of single Chl a molecules absorbing at 675 nm are broadened because of the Foerster energy transfer towards the red-most pigments. Low-temperature spectroscopy on single PS I trimers indicates that two subgroups of pigments, which are present in the red antenna pool, differ by the strength of the coupling with the protein environment and by the efficiency of the triplet state quenching. Based on single molecule and hole burning data, we envisage the dimeric nature of the strongly phonon coupled red-most Chl state.     

Structure in the emission from pyrene evaporated films

Emission spectra and decay times of fluorescence of pyrene thin films prepared by evaporation onto substrates at liquid nitrogen temperature were measured. Structure in the emission from films warmed slowly up to higher temperature is found to the higher energy side of the excimer emission band. The decay time is about 410 ns at temperatures between 110 K and 210 K. But the emission from the film warmed up to a temperature above 210 K shows only the excimer emission. These results are discussed in relation to an amorphous structure in the pyrene evaporated thin film.     

Optical properties and morphology of thin diindenoperylene films

Thin films of diindenoperylene deposited on weakly interacting substrates (quartz) are characterized with scanning probe microscopy techniques at room temperature and by pico-second time-resolved fluorescence spectroscopy between 5 and 300 K. Pronounced T-dependencies of fluorescence spectra and decays are found. The interplay between two fluorescence series in a narrow temperature range has been spectrally and temporally resolved. The possible origin of the observed series, competing energy transfer and quenching processes is discussed.