Luminescence Properties of Poly(3-Methoxythiophene)—Bithiophene Composite Oligomers

The electronic absorption and fluorescence spectra of electrosynthesized poly(3-methoxythiophene)— bithiophene (PMOT-BT) composite oligomers were studied in organic solution (DMSO) and/or in the solid state on ITO plates. Different spectral properties (absorption and fluorescence maximum wavelengths, fluorescence quantum yields, etc.) were found to depend on the bithiophene initial concentration used during electrosynthesis and, subsequently, on the film composition and oligomer chain length.     

橄榄油的聚集荧光猝灭及吸收光谱特性的研究

素有“液体黄金”之称的橄榄油已成为健康食用油的代名词,不仅身价陡增,而且在非产地市场也已成为一种畅销油。在橄榄油检测技术中光谱法与其他技术相比具有快速、无损、无样品处理等优势而备受关注,而不同的光谱检测方法在检测的物质成分上各有侧重,例如红外光谱法侧重于脂肪酸含量的检测、拉曼光谱法侧重于分子的检测、荧光光谱法侧重于光敏物质的检测以及吸收光谱法侧重于光敏物质和不饱和脂肪酸的检测等。荧光及吸收光谱对光敏物质反应极其灵敏,而橄榄油富含叶绿素等光敏物质,因此荧光及吸收光谱成为一种鉴别橄榄油的有效技术手段。叶绿素是一种含有环卟啉结构的有机分子,该类分子结构具有吸光特性,且不同的叶绿素吸收光谱各异,其中绿色植物的叶绿素a含量最多。为深入研究叶绿素的吸收光谱及荧光特性在橄榄油鉴别中的应用,将特级初榨橄榄油中掺入不同比例的玉米油,已达到间接调控橄榄油中叶绿素含量的目的,测量不同掺伪比例橄榄油的荧光及吸收光谱并研究与叶绿素浓度的相关性,以此来研究叶绿素浓度与掺伪量对橄榄油吸收光谱及荧光特性的影响。取10份同批次的特级初榨橄榄油,将其中9份按照等比例稀释,并对10份样品按照掺伪量依次排序;依次采集这10份样品的荧光及吸收光谱,比较叶绿素浓度与掺伪量的相关性及对这两种光谱技术在橄榄油鉴别中的影响。随着叶绿素浓度的上升,荧光强度由弱变强,并在某一时刻后会出现荧光强度急剧减弱的现象,即聚集荧光猝灭。这种现象主要是由于叶绿素的环卟啉分子结构引起的分子间π-π作用,使未被激发的低能分子与高能分子堆叠在一起,能量的辐射跃迁（荧光）也转变为分子间的能量转移（热能交换）。对于吸收光谱,随着叶绿素浓度的上升,吸收光谱的强度也逐渐增强。橄榄油中叶绿素吸收的能量主要去向包括镁电子辐射跃迁产生荧光以及分子间热能交换两部分,而橄榄油的吸收光谱并未出现类似于聚集荧光猝灭的现象,且吸收光谱强度与掺伪浓度间存在近似线性相关的关系。结果表明：当聚集荧光猝灭出现时,叶绿素吸收的能量仍然与浓度呈线性相关,此时高、低能分子堆叠引起的热能交换效率提高。     

The effect of annulation of benzene rings on the photophysics and electronic structure of tetraazachlorin molecules

The photophysics and electronic structure of tribenzotetraazachlorins (H₂, Zn, and Mg), which are novel analogues of phtalocyanines, have been studied experimentally and theoretically. At 293 K, the electronic absorption, fluorescence, and fluorescence excitation spectra are recorded and the fluorescence quantum yield and lifetime, as well as the quantum yield of singlet oxygen generation, are measured; at 77 K, the fluorescence, fluorescence excitation, and fluorescence polarization spectra are recorded and the fluorescence lifetime values are measured. The dependences of the absorption spectra and photophysical parameters on the structure variation are analyzed in detail. Quantum-chemical calculations of the electronic structure and absorption spectra of tribenzotetraazachlorins (H₂, Mg) are performed using the INDO/Sm method (modified INDO/S method) based on molecular-geometry optimization by the DFT PBE/TZVP method. The results of quantum-chemical calculations of the electronic absorption spectra are in very good agreement with the experimental data for the transitions to two lower electronic states.     

An investigation on fluorescence quenching of certain porphyrins by colloidal CdS

Certain porphyrin derivatives namely meso-tetraphenylporphyrin (TPP), meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP), meso-tetrakis(4-sulfonatophenyl)porphyrin (TSPP) were examined as sensitizers for colloidal CdS. The interaction of these porphyrins and colloidal CdS were studied by absorption, infrared, steady state and time resolved fluorescence spectroscopy and transient absorption techniques. The apparent association constants (K_app) resulting from adsorption of porphyrins on CdS surface were calculated from both absorption and fluorescence studies and they agree well. Using all the spectroscopic measurements we confirmed that the interaction between porphyrins and colloidal CdS occurs through ground state complex formation and the quenching follows static mechanism.     

Optical time-resolved study of the excitation dynamics*

Transient behaviour of the excited states originated from the neutral and the charged species is discussed using data from time-resolved experiments. Complex transient characteristics obtained for the slightly charged poly-(bithiophene) film during electrochemical doping were explained in terms of sequential molar fraction changes of the neutral species, the radical cation and the π-dimerized radical cations. Femtosecond transient absorption measurement carried out in time range of 0-4 ns for a two-photon excited dye reveals a multi-exponent decay with well separated relaxation times and the distinct relaxation mechanisms. At high irradiance and a sufficient fluence, the multi-photon excitation processes affect the subpicosecond response and lead to formation of the photo-products.     

Fluorescence Characteristics of Variously Charged Asymmetric Monomethine Cyanine Dyes in the Presence of Nucleic Acids

Three asymmetric monomethine cyanine dyes bearing one, two, and three positive charges have been synthesized, and their absorption and fluorescence characteristics in the presence of nucleic acids were studied. The maxima of their longest wavelength absorption band lie between 500 and 520 nm. The dyes do not show fluorescence of their own in TE buffer (pH = 7.5), but become strongly fluorescent (Q_F = 0.2–0.6) on binding to double-stranded DNA. The fluorescence maxima of the investigated dye-dsDNA complexes are in the region of 530–550 nm. The influence of the dye/DNA ratio on both the position and intensity of the fluorescence maxima of the complexes is investigated.     

四取代酞菁金属配合物的紫外-可见吸收光谱和荧光发射光谱研究

报道了16种含哌嗪或含哌啶四取代酞菁金属配合物{R4PcM,R=2-[4-(2-磺基乙基)哌嗪-1-基]乙氧基(SPEO—)、2-(哌啶-1-基)乙氧基(PEO—);取代位置分别在α位和β位;M=Zn(Ⅱ),Ni(Ⅱ),Co(Ⅱ), Cu(Ⅱ)}的UV-Vis吸收光谱和荧光发射光谱的测定,探讨了中心金属离子、取代基种类及其取代位置、溶剂等因素对酞菁金属配合物UV-Vis吸收光谱和荧光发射光谱性质的影响。结果表明:R4PcM的Q带λ_max落在681～718 nm范围内,与相同中心金属离子的无取代酞菁金属配合物(669～671 nm)比较都发生了不同程度的红移,荧光发射光谱与UV-Vis吸收光谱呈镜像关系,特别的是两种β位取代中心金属离子为Zn(Ⅱ)的酞菁金属配合物[β-(SPEO)₄PcZn,β-(PEO)₄PcZn]具有极高的摩尔消光系数、较大的荧光量子产率和较长的荧光寿命,有望开发成新型的光动力诊疗用光敏剂。     

Photophysical Properties of some 1,3,4-Oxadiazole Derivatives Containing Phenolphtalein,Fluorene and Bisphenol A Units

The photophysical properties of the three 1,3,4-oxadiazole derivatives containing fluorene (Ox-FL); fluorene and phenolphtaleine (Ox-FL-FF); or fluorene and bisphenol A (Ox-FL-BPA) moieties in the main chain were investigated by the fluorescence and absorption spectroscopy in different solvents and in the solid state. The electronic absorption spectra included a strong absorption band located in the 270–395 nm region, with a maxima around at 302 nm. The fluorescence excitation spectra were also characterized by one broad band, appearing in the wavelength range of 220–340 nm. All samples displayed the emission bands around 356–373 nm and exhibit high quantum yields ranged from 31.61 to 90.77%, in chloroform solution. The sensitivity of the emission spectra on medium characteristics (polarity, acidity and basicity) were evaluated by using the Catalan solvent scale and the fluorescence titration with a dilute acid solution.     

Photoinduced interaction of colloidal TiO2 nanoparticles with lysozyme: Evidences from spectroscopic studies

The interaction between colloidal TiO₂ nanoparticles and lysozyme (LYSO) was studied using absorption, steady state and time resolved fluorescence, FT-IR and synchronous fluorescence spectroscopic measurements. The apparent association constant has been deduced from the absorption spectral changes of LYSO-colloidal TiO₂ nanoparticles using Benesi-Hildebrand equation. The number of binding sites and the apparent binding constant were calculated from relevant fluorescence data. Based on Forster's non-radiation energy transfer theory, distance between the donor (LYSO) and the acceptor (TiO₂) has also been calculated. The conformational changes of LYSO have been analyzed by means of FT-IR and synchronous fluorescence spectroscopy. In addition, the effect of metal ions on the binding constants of LYSO-TiO₂ complex has also been discussed.     

光谱法研究EGCG-Cu(Ⅱ)与ctDNA的相互作用

研究了EGCG-Cu(Ⅱ)-ctDNA系统的荧光光谱,电子吸收光谱和共振光散射光谱(RLS)。与EGCG-Cu(Ⅱ)二元配合物比较,EGCG-Cu(Ⅱ)-ctDNA三元体系光谱显示以下特征：(1)荧光光谱的发射位置没有变,荧光强度显著增强,并且三元体系的荧光强度随着DNA浓度增大而增大。在适宜的条件下,Cu(Ⅱ)-EGCG 配合物有望成为检测ctDNA的荧光探针;(2)电子吸收光谱有明显的增色效应;(3)共振光散射强度也增强。三种光谱的特征显示,EGCG-Cu(Ⅱ)配合物与核酸之间主要依靠插入作用和静电引力结合。由于配合物的插入,使系统的荧光强度增强,而静电作用使其电子吸收光谱和共振光散射光谱产生增色效应。酸度和离子强度对三元系统荧光强度的影响也进行了实验和讨论。