Luminescence Spectra Of Solutions Research Articles

Highly Luminous Sky-Blue Organic Light-Emitting Diodes Based on the Bis[(1,2)(5,6)]indoloanthracene Emissive Layer

An in-depth analysis of the electro-optical and light-emissive properties was carried out with a new fused heteroacene, the bis[(1,2)(5,6)]indoloanthracene. The compound was synthesized in a straightforward bidirectional manner from 1,4-dibromo-2,5-diodobenzene utilizing a reaction cascade of isomerization and cyclization sequences. Bis[(1,2)(5,6)]indoloanthracene exhibits bright luminescence with high quantum yield in solution as well as in the solid state. By using this novel semiconductor as active layer, an efficient organic light-emitting diode (OLED) has been fabricated for which its emission pattern resembles at least two emitters in a single emissive region originated from the same molecule. One has its origin from the single molecule and is similar to the luminescence spectra in solution, whereas the other functions through the formation of aggregates being similar to the emission pattern found with crystals of bis[(1,2)(5,6)]indoloanthracene. As a result, bright sky-blue OLEDs with very high lum...

Luminescence properties of three structures built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate and alkaline metals (Na, K and Rb)

The structures of three salts of 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate with alkali metals (Na, K and Rb) are related to their luminescence properties. The Rb salt, rubidium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate, Rb(+).C(8)HN(4)O(2)(-), is isomorphous with the previously reported potassium salt. For the Na compound, sodium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate dihydrate, Na(+).C(8)HN(4)O(2)(-).2H(2)O, two independent sodium ions, located on inversion centers, are coordinated by four water molecules each and additionally by two cyano groups for one and two carbonyl groups for the other. The luminescence spectra in solution are unaffected by the nature of the cation but vary strongly with the dielectric constant of the solvent. In the solid state, the emission maxima vary with structural features; the redshift of the maximum luminescence varies inversely with the distance between the stacked anions.

Crotonization in the Benzo[a]acridine Series. Synthesis of Naphtho[2,1‐j][1,7]phenanthroline Derivatives.

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Crotonization in the benzo[a]acridine series. Synthesis of naphtho[2,1-j][1,7]phenanthroline derivatives

8,9,10,11-Tetrahydrobenzo[a]acridin-11-one reacted with aromatic aldehydes to give the corresponding 10-arylmethylidene-8,9,10,11-tetrahydrobenzo[a]acridin-11-ones. Reactions of the latter with malononitrile in the presence of a base catalyst led to the formation of polynuclear partially hydrogenated systems, 2-alkoxy-4-aryl-5,6-dihydronaphtho[2,1-j][1,7]phenanthroline-3-carbonitriles, whose absorption and luminescence spectra in solution and polycrystalline state were studied.

Optical, Electrochemical, and Catalytic Properties of the Unsaturated Host Pd3(dppm)3(CO)2+and Pd4(dppm)4(H)2+2Clusters: An Overview

This paper presents an overview of the optical, photophysical, and photochemical properties including UV-visible and luminescence spectra in solution at 298 and 77 K, along with electrochemical, and catalytic behavior under reduction conditions (for both thermally and electrochemically assisted systems) of the tri- and tetranuclear Pd3(dppm)3(CO)2+ and Pd4(dppm)4(H)2+ 2 clusters (dppm=bis(diphenylphosphino)methane). This review is also complemented with relevant information about their syntheses, molecular and electronic structures supported from computer modeling, EHMO and DFT calculations, and their host-guest behavior with anions and neutral molecules, in relation with their observed reactivity.

Peculiarities of Triplet Exciton Jump Mechanism in Unconjugated Polymers with Pendant Benzophenone-Type Groups

Copolymer of methylmethacrylate with methacrylate of monopropandiole ether of benzophenonecarbone acid (BCA-MMA) with different contents of the benzophenone-type groups has been studied. Investigation of absorption and luminescence spectra of solutions of BCA-MMA, dependence of phosphorescence intensity on intensity of exciting light and dependence of polarization degree on content of BCA links in copolymer macromolecule has been carried out. Basing on data obtained it was found that the migration of t-excitons and their effective annihilation in macromolecules of BCA-MMA took place starting from 32.6% content of the benzophenone-type links. Using computer calculation for a geometry optimization of the studied polymers the average distance between chromophores for BCA-MMA containing ∼20% and ∼33% of the benzophenone-type links was determined. It is asserted that the critical jump distance for the triplet excitons in studied polymers is in these limits and is equal approximately 20 Å.

Tuning the Optoelectronic Properties of Pyridine-Containing Polymers for Light-Emitting Devices

Increased electron affinity and improved electron-transporting properties are lent to polymers based on pyridine when compared to benzene. Here, the synthesis of new pyridine-containing conjugated polymers, such as those shown in the Figure, are described. Their optical absorption and luminescence spectra in solution and thin films are also investigated as is their potential as electron-transporting layers in LEDs.

Spectroscopic Studies of Fullerene Aggregates

The growth and structure of fullerene (C60 and C70) aggregates in single and binary mixed-solvent solutions were examined by light scattering and photoluminescence spectroscopy. Solute aggregation exhibiting reaction-limited kinetics was observed to occur over a period of several days in ∼1 mM C60 solutions in benzene. Aggregation was irreversible and could be suppressed by addition of a soluble radical scavenger, suggesting a radical mechanism for aggregate formation. Dynamic light scattering measurements determined that the aggregates attain a hydrodynamic radius of ∼300 nm before sedimentation occurs. Solutions containing stable suspensions of fullerene aggregates were also prepared by addition of a poor solvent to a solution of fullerene in a strong solvent. Both static and dynamic light scattering methods were used to determine the mass, hydrodynamic radius, radius of gyration, and fractal dimension of the aggregates. Photoluminescence spectra of aggregates were compared with those of the crystalline materials. The luminescence spectra of solutions containing aggregates were found to differ substantially from the luminescence spectra of unassociated fullerene. The chief effect of aggregate formation is the appearance of excimer-like features in the photoluminescence spectrum.

Optical spectra and excitations in phenylene vinylene oligomers

Experimental results of optical absorption spectra, photoluminescence spectra due to singlet exciton emission and photoinduced absorption spectra due to triplet-triplet transitions of triplet excitons for several oligomers of poly( p-phenylene vinylene) are reported. From the red-shift of the peaks with increasing chain length, the effective conjugation length for long-chain precursor-route samples of the polymer are estimated to be about 10 to 17 repeat units. Theoretical studies, using the valence-effective Hamiltonian (VEH) technique, of the effects of ring torsions upon the electronic properties are also reported. Comparison between absorption and luminescence spectra in solution and in the solid state shows a blue-shift for the solution spectra; this is modelled in terms of a greater degree of ring torsion for these oligomers in solution.

Spectral and luminescence properties of ethanol solutions of rhodamine 6G under picosecond excitation

Investigations were made of the absorption and luminescence spectra of ethanol solutions of rhodamine 6G as a function of concentration at room and liquid nitrogen temperatures. Light from a steady-state source and picosecond pulses from a neodymium glass laser were used for excitation. Under picosecond excitation, it was found that the luminescence spectrum of solutions with high concentrations (10?2 mole or higher) exhibited a long-wavelength band with ?max = 670 nm. At liquid nitrogen temperature, the luminescence spectrum of these solutions had two maxima at 620 and 670 nm. Measurements of the luminescence lifetime of these bands showed that it was of the same order as the fluorescence lifetime of rhodamine 6G molecules in ethanol. The observed long-wavelength luminescence was attributed to associated rhodamine 6G molecules.

Regularities in the luminescence spectra of solutions with molecular anion impurities

This article deals with the absorption, excitation and luminescence spectra of frozen aqueous solutions of the halide salts and acids with molecular anion impurities CN -, SCN -, SeCN - and CNO -. It is shown that the spectra at 4.2°K display vibronic structure which is explained by the interaction of electronic transition with intramolecular oscillations of the impurity. Conclusions are also deduced from the results of investigation of temperature dependence of the quantum emission efficiency and the Raman spectra of such systems.