Single-layered light-emitting diodes possessing methoxy-modified pyrazoloquinoline dyes in poly-N-vinylcarbazole matrix

A principal opportunity to operate by current-voltage and electroluminescent-current dependences for the single-layered light-emitting diodes (LED) on the basis of the polyvinylcarbazole (PVK) polymers doped by methoxy-substituted pyrazoloquinoline (PQ) emitting dye chromphore is demonstrated. The principal light-emitting parameters in the architecture ITO/PQ: PVK/Ca (Al) were investigated. The maximally achieved quantum efficiency of the investigated LED was equal to about 0.87% and corresponded to the brightness about the 44 Cd/m². The absence of blue shift for the electroluminescence (EL) compared to PL may indicate on an absence of near-the-surface exciton diffusion for the methoxy-PQ contrary to the phenyl-methyl-substituted PQ. The quantum chemical calculations have shown principal role of the dye chromophore state dipole moments in the observed carrier kinetics determining the EL.     

Emissive Properties and Intramolecular Charge Transfer of Pyrazoloquinoline Derivatives

The fluorescence properties of several pyrazoloquinoline derivatives were performed by stationary as well as by time-resolved spectrosopy. Non-donor-substituted compounds show a high quantum yield; transition dipole moments of absorption and fluorescence as well as experimental and calculated lifetimes are in excellent agreement. The donor-substituted compound DMA-DPPQ exhibits a charge transfer fluorescence in polar solvents. Additionally, dual fluorescence appears in polar protic solvents. The nature of the charge transfer state is discussed with respect to the the TICT model.     

Thermoluminescence of the blue light-emitting system based on poly(9-vinylcarbazole) doped with a pyrazoloquinoline dye

We have investigated the charge carrier trapping and recombination mechanisms in electroluminescent systems based on poly(9-vinylcarbazole)/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole blend, used as the matrix, and the deep blue light-emitting pyrazoloquinoline dye-1-H-pyrazolo[3,4-b]quinoline (PAQ8) dopant. The thermoluminescence studies have shown that the charge carrier trapping occurs on the dye molecules as well as on the matrix components. The traps localized on the PAQ8 molecules compete with the others available in the system, however at higher concentrations of the dye a role of these traps increases. Spectral analyses of the thermoluminescence have indicated that even at low concentration of PAQ8, the dye molecules constitute the dominating recombination centres in the system.     

Application of modified Pictet-Spengler reaction for the synthesis of thiazolo- and pyrazolo-quinolines

Two new thiazole and pyrazole-based arylamine substrate have been used for the Pictet-Spengler reaction. This is in contrast to the traditionally used indole/imidazole-based aliphatic amine substrates that has remained in use for the last ∼100 years. The condensation of both the substrates with a variety of aldehydes in the presence of 2% TFA-DCM at 0° for 30 min or pTsOH in toluene at reflux led to the synthesis of thiazoloquinolines and pyrazoloquinolines, respectively. Unlike aliphatic amine substrates, our substrates readily underwent Pictet-Spengler cyclization even with aldehydes having electron donating group. The studies are based on a new concept proposed by us that arylamines linked to an activated heterocyclic ring can lead to a variety of second-generation substrates for the Pictet-Spengler cyclization. Our studies open up new avenues for the application of Pictet-Spengler reaction beyond syntheses of the tetrahydroisoquinolines and tetrahydro-β-carbolines.