Excited state complex and electroluminescence in TPD-based single layer device

N-N′-diphenyl-N,N′-(bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) (TPD), was used to fabricate single layer devices (ITO/TPD/Ca/Al). A near-white emission (CIE coordinate of 0.25, 0.24) is observed in electroluminescence (EL) of the single layer device with prominent emission bands at 400, 475 and 670 nm. Steady state and time-resolved emission spectra of spin-coated and annealed TPD films and TRES and TRANES analysis confirmed that emission at 400 and 475 nm are due to monomer and excimer emission, respectively. The origin of the red emission at 670 nm in EL is discussed.     

TRANES Spectra of Fluorescence Probes in Lipid Bilayer Membranes: An Assessment of Population Heterogeneity and Dynamics

Time-resolved fluorescence of eight fluorescence probes were studied in EggPC bilayer membrane vesicles. Emission wavelength dependent fluorescence decays were analyzed in a model-independent way to obtain time resolved area normalized emission spectra (TRANES). The TRANES spectra of the probes studied were classified into four types: (1) spectra that are identical at all time (one emissive species), (2) spectra that show an isoemissive point (two emissive species), (3) spectra that shift continuously with time (slow solvation dynamics or multiple species), and (4) spectra that shift for a short time and thereafter one or two emissive species are indicated. The TRANES spectra of these eight probes, except RH421, belong to the type 1, 2, or 4. The continuous shift of the TRANES spectra that was observed for the probe RH421 is attributed to multiple ground state species and not due to slow solvation dynamics.     

Fluorescence spectrum characteristic of ethanol--water excimer and mechanism of resonance energy transfer

The steady-state fluorescence spectrum characteristic of ethanol--water excimer has been studied in this paper. By analysing the features of the sharp emission spectrum with fine structures in a shortwave band and the characteristics of the broad and featureless fluorescence peaks in the longwave band, one can conclude that the excimers are formed between the new ethanol--water cluster molecules in the excited state and the ground state through the interaction among different chromophores. The excitation spectra in the two fluorescence bands have been studied, and their emission mechanisms have been ascertained based on the energy transfer theory. Furthermore, the critical distance of the resonance energy transfer has been calculated.     

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.     

有机混合薄膜中的F(o)rster能量转移

通过掺杂不同的染料有机电致发光器件可以得到不同颜色的光发射。掺杂小分子有机材料?p酸四甲酯perylene-3,4,9,10-tetracarboxylicacid(TMEP)到蓝色发光聚合物poly(N-vinyl-carbazole)聚乙烯基咔唑(PVK),得到了很好的绿光发射。TEMP掺杂质量分数为0.01时,295. 5nm激发波长的荧光光谱可以明显观察到在420 nm处PVK和530 nm处TEMP的发射峰值;当TMEP掺杂质量分数达到0.05～0.10之间,器件的电致发光光谱和荧光光谱发射峰几乎完全被TEMP的绿光所占据。光谱的转移归因于从聚合物PVK到小分子有机材料TMEP的Forster能量转移。荧光光谱中随着TMEP掺杂浓度的的增大发射峰值有明显的红移,这种现象被归因于在TMEP高浓度掺杂情况下激基缔合物的形成。激基缔合物的形成从TMEP在薄膜状态下与溶液状态下的荧光光谱的比较中得到证实。     

Photoluminescence of pentyl-cyanobiphenyl in liquid-crystal and solid-crystal states

The stationary and time-resolved photoluminescence spectra of n-pentyl-n′-cyanobiphenyl (5CB) are studied in a mesophase and solid-crystal state. The photoluminescence spectra of 5CB are determined by the molecular configuration and the intramolecular charge transfer in the excited state. It is shown that in the mesophase and solid-crystal state, 5CB exhibits along with monomer radiation at least two types of excimer radiation from different pre-dimer states.     

Analysis and kinetic model of a high-pressure KrI excimer emission in a novel capacitively coupled rf lamp

We report and analyze KrI^*/I₂ ^* multi-emission spectra (160–360 nm) generated in a novel capacitively coupled 13.56 MHz rf lamp. The 13.56 MHz rf lamp, configured to avoid electrodes internal to the plasma, is used to generate a number of excimer emissions in the UV and visible spectral regions with potential biological, physical, and chemical application. We found that the total gas pressure strongly influenced the emission efficiency of KrI and I₂ excimers in the pressure range of 200 to 1200 torr. A simple kinetic model was developed to explain the observed KrI^* and I₂ ^* pressure dependence. This work provides valuable experimental information (in the high pressure regime) for obtaining accurate potential energy curves, to determine the vibrational distribution in the emitting states for KrI. PACS 52.80.Pi; 32.30.JC; 52.80.Yr; 42.72.Bj     

Excimer emission of crystalline naphthalene

Excimer emission of naphthalene has been observed in microcrystals obtained by grinding single crystals mechanically and in evaporated films. The emission spectrum of the excimer in the microcrystal was equal to that in the evaporated film. The decay times of both excimer emissions were about 140 ns at 77 K. The temperature dependence of these decay times has been interpreted by the distribution of the excimers in thermal equilibrium between two vibrational states.     

Application of Multivariate Curve Resolution–Alternate Least Square Technique on Extracting Pure Spectral Components from Multiple Emitting Systems: a Case Study

Multiple emitting components in a fluorophoric system often produce complicated emission spectra. Extracting the individual spectral information from the composite spectra is important in order to comprehend the photophysical processes occurring in the multifluorophoric systems. Although the combination of Principal Component Analysis and Multivariate Curve Resolution-Alternate Least Square (PCA/MCR-ALS) technique is a well-known approach for curve deconvolution, its applicability in the spectral deconvolution of vibronically and electronically mixed up emitting systems as well as systems merged up with multiple electronic bands without a priori knowledge of the individual emitting species, is not properly studied. The present work highlights the strength of PCA/MCR-ALS in retrieving pure spectral information from the set of complex spectra arising out of the regular variation of causative factors that result in the variation of spectral composition. The retrieval of the emission bands utilizing the PCA/MCR-ALS technique has been made without having a priori information of the emitting species present in the multifluorophoric systems and the resolved spectra correspond well with the fluorescence spectra of the individual chemical species. The common curve fitting methods such as Gaussian and Lorentzian techniques have been found to be unsuccessful in providing meaningful photophysical information through the retrieved spectra. A comparative study of the curve fitting techniques MCR-ALS, Gaussian and Lorentzian in a set of complicated emission spectra of (i) pyrene and its excimer, (ii) pyrene and its excimer in presence of benzo[a]pyrene, and (iii) fisetin in bile salt medium is presented herein in details.     

Immobilization of pyrene via diethylenetriamine on quartz plate surface for recognition of dicarboxylic acids

A novel photo-luminescence film has been prepared by immobilizing pyrene on a quartz plate surface via diethylenetriamine. Imino structure was intentionally introduced into the long flexible spacer due to their hydrogen bond forming abilities with carboxylic acids. It has been found that the film shows combined monomer and excimer emission of pyrene both in wet and dry states. Steady-state and time-resolved fluorescence emission measurements demonstrated that the excimer emission mainly came from direct excitation of ground state dimers, and/or monomers in aggregated state. The structures of the excimers formed during the excitation are mixtures of “standard excimers” and “distorted excimers” of the fluorophore moieties. Fluorescence lifetime measurements showed that the decay of the film is complex, and a four exponential fit is necessary for getting a satisfied result. The photophysical behavior of the present film could be rationalized by employing the model proposed before. Sensing property studies showed that the emission of the film is sensitive to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, etc. In contrast, presence of monocarboxylic acids, such as formic acid and acetic acid, had little effect upon the fluorescence emission of the film. Compared with the films taking ethylenediamine or 1,3-diaminopropane as their spacer component, introduction of diethylenetriamine into the spacer improved the performance of the film greatly. In addition, the sensing process is reversible, and the film is stable within a number of months provided it is properly preserved. These characteristics showed that the film is worthwhile for further exploration.     

Luminescence studies of o-hydroxy p-amino and p-dimethylamino methyl benzoate

Steady-state and time-resolved spectroscopic studies of two bisubstituted derivatives of methyl benzoate dissolved in methylcyclohexane (McH), tetrahydrofuran (THF), and ethanol (EtOH) have been performed at 293 and 77 K. The compounds under study are capable of showing multimode fluorescence emission at room temperature. The kind of emission, i.e., locally excited state emission Fl(LE), proton-transfer emission Fl(PT) and twisted intramolecular charge-transfer emission Fl(CT) dependent on the solvent. Low temperature measurements show that for those molecules a phosphorescence enhancement via a proton-transfer tunneling is observed. For the molecules under study compositeness of the emission process is explained on an energy scheme, which is based on experimentally determined and theoretically calculated data. Stated dynamic Stokes shift and phosphorescence red-edge effect indicates that both molecules form an inhomogeneous emitting system in solvents used. The experiments are supported with quantum chemical semiempirical calculations.     

1-羟基-5-十六烷氧基-萘LB膜的荧光光谱研究

１┐羟基┐５┐十六烷氧基┐萘ＬＢ膜的荧光光谱研究李小灵赵冰吴玉清徐蔚青吴英（吉林大学超分子结构与谱学开放实验室长春市１３００２３）Ｓｔｒｕｃｔｒｕｅｏｆ１┐ｈｙｄｒｏｘｙ１┐５┐ｈｅｘａｄｅｃｙｌｏｘｙ┐ＮａｐｈｔｈａｌｅｎｅＬＢＦｉｌｍｓＳｔｕｄ...     

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.     

有机电致发光白光器件的研究进展

在十多年的时间里,有机电致发光二极管(Organic Lightemitting Diodes,OLEDs)的研究和应用取得了长足的进展。有机电致发光器件具有许多优点,例如:自发光、视角宽、响应快、发光效率高、温度适应性好、生产工艺简单、驱动电压低、能耗低、成本低等,因此有机电致发光器件极有可能成为下一代的平板显示终端。有机电致发光白光器件因为可以用于全彩色显示和照明,已成为OLED研究中的热点。介绍了有机电致发光白光器件的研究进展,按发光的性质将白光器件分为荧光器件和磷光器件两类,按发光层数将白光器件分为单层和多层器件,对相关材料、器件结构、发光机理等方面进行了讨论。     

A method to obtain ground state electroluminescence from 1.3μm emitting InAs/GaAs quantum dots grown by molecular beam epitaxy

1.3μm emitting InAs/GaAs quantum dots(QDs) have been grown by molecular beam epitaxy and QD light emitting diodes(LEDs) have been fabricated.In the electroluminescence spectra of QD LEDs,two clear peaks corresponding to the ground state emission and the excited state emission are observed.It was found that the ground state emission could be achieved by increasing the number of QDs contained in the active region because of the state filling effect.This work demonstrates a way to control and tune the emitting wavelength of QD LEDs and lasers.     

Fluorescence properties of Bi4Ge3O12(BGO) single crystals under laser excitation: Excited state dynamics and saturation effects

Laser-excited techniques were used to investigate the optical properties of bismuth germanate crystals. Absorption, reflectivity, excitation, emission, lifetime, time-resolved fluorescence, photoconductivity, thermally stimulated conductivity measurements were performed at various temperatures on single crystals of different origins.The absorption is shown to occur in bismuth and germanate centers while both intrinsic and perturbed Bi³⁺ ions together with impurities contribute to the total fluorescence.The emission mechanism at room temperature involves a thermally activated energy migration, and at low temperature localized emitting centers. Formation of deep holes in the wide emission band at room temperature reveals saturation effects on various luminescent centers, promoted by energy migration. Trapped exciton models are proposed to explain the excited state dynamics occurring at low and room temperature.     

The effect of bromine substitution on the charge-transfer emission of the complex of phenanthrene and tetracyanobenzene

The absorption spectra of the charge-transfer complexes of sym-tetracyanobenzene (TCNB) with phenanthrene, 9-bromophenanthrene, and 9,10-dibromophenanthrene are measured in chloroform solutions at room temperature. The total emission and phosphorescence spectra of the donors and the complexes are measured at 77 K in rigid glasses. The phosphorescence decay lifetimes are determined for phenanthrene, TCNB, and for the phenanthrene-TCNB complex, and a decrease in the phenanthrene-TCNB complex lifetime relative to the lifetimes of the two components is observed. The luminescence spectra of the complexes exhibit both a red shift and a lack of structure as compared with the donor spectra. The results are interpreted, in agreement with the results of Iwata et al. for the phenanthrene-TCNB complex (1), as an indication that there is a considerable degree of charge-transfer character in the lowest triplet state (T₁). Bromine substitution leads to a decrease in the energy of the phenanthrene triplet state. As a result, the energy gap between the donor molecule triplet state and the complex charge-transfer triplet state decreases from phenanthrene, to 9-bromophenanthrene, to 9,10-dibromophenanthrene. The results suggest that the proximity of these two triplet states in 9,10-dibromophenanthrene and its charge-transfer complex leads to some local donor triplet state character in the emitting complex triplet state.     

Investigation of Abnormal Long‐Wavelength Fluorescence Emissions Occurring in Binary Organic Nanoparticle Films

In some fluorophores with planar groups, a long‐wavelength emission band different from their native one can sometimes be observed. The main cause of this long‐wavelength band is excimer formation. It is generally accepted that once condensed in the solid state, whether fluorophores can exhibit excimer emission or not depends only on their molecular structure and packing. However, here it is shown that there are exceptions when fluorophores are present in nanoparticles (NPs), where excimer emission can be affected by the environment surrounding the NPs, even in the solid state. It is found that in some binary NP films consisting of fluorophore NPs and other NPs, unusual long‐wavelength bands ascribed to excimer emission can be activated, even though these bands are absent from the photoluminescence spectra of the pure fluorophore NP films. This finding is beneficial to better understand and control excimer emissions. In addition, such a binary NP system provides an ideal platform to investigate the interplay between two fluorophores, because it keeps them effectively separated while maintaining suitable spatial distances for exciton migration and dipole–dipole interactions. This work also provides evidence for the long‐debated origin of the green emission band (g‐band) of fluorene‐based fluorophores.     

Photophysical Studies on the Interaction of Acridinedione Dyes with Universal Protein Denaturant: Guanidine Hydrochloride

Photophysical studies of photoinduced electron transfer (PET) and non-PET based acridinedione dyes with guanidine hydrochloride (GuHCl) were carried out in water and methanol. Addition of GuHCl to photoinduced electron transfer (PET) based acridinedione dye (ADR 1) results in a fluorescence enhancement, whereas a non-PET based dye (ADR 2) shows no significant change in the fluorescence intensity and lifetime. Addition of GuHCl to ADR 1 dye in methanol results in single exponential decay behaviour, on the contrary a biexponential decay pattern was observed on the addition of GuHCl in water. Absorption and emission spectral studies of ADR 1 dye interaction with GuHCl reveals that the dye molecule is not in the protonated form in aqueous GuHCl solution, and the dye is confined to two distinguishable microenvironment in the aqueous phase. A large variation in the microenvironment around the dye molecule is created on the addition of GuHCl and this was ascertained by time-resolved area normalized emission spectroscopy (TRANES) and time-resolved emission spectroscopy (TRES). The dye molecule prefers to reside in the hydrophobic microenvironment, rather in the hydrophilic aqueous phase is well emphasized by time-resolved fluorescence lifetime studies. The mechanism of fluorescence enhancement of ADR 1 dye by GuHCl is attributed to the suppression of the PET process occuring through space.     

Spectral Investigations of thf Photoreactions of Flavomononucleotide (FMM) Immoblized in Polymer Film

The absorption, fluorescence and photo-acoustic spectra of flavomonnnucleotide (FMM) molecules embedded in polyvinyl alcohol film were measured for illuminated and for stored in darkness samples. The effect of illumination depends an pigment concentration, and it is connected with FMN excimers formation. The FMN excimer formation prevented the photodestruction of isoatloxazine ring.