On the spectral properties of methyl and methoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxalines: Experiment and DFT/TDDFT calculations.

Paper reports the synthesis and spectroscopic studies of two novel 1,3-diphenyl pyrazoloquinoxaline (PQX) derivatives with 6-substituted methyl (MePQX) or methoxy (MeOPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Other photophysical constants, such as the fluorescence lifetime and quantum yield, radiationless and radiative rate constants, electronic transition dipole moments, give complete characterization of MePQX and MeOPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with the results of quantum-chemical analysis using density functional theory (DFT/TDDFT) methods based on hybrid and long range corrected (LRC) exchange-correlation (xc) functionals in combination with solvation self consistent reaction field model. Comparing to conventional hybrid xc-functionals, the DFT/TDDFT calculations using LRC xc-functionals yield considerably more accurate description of optical absorption and fluorescence emission spectra. The best description of the absorption-emission circle provides the model assuming that optical absorption takes place from preferably flat or weakly twisted molecular conformations in the ground state, as particularly is suggested by the geometrical DFT optimization, whereas the fluorescence emission would be expected from more twisted molecular conformations in the excited state.

Novel dipyrazolopyridine derivatives as deep blue emitters for polymer based organic light emitting diodes.

Paper reports synthesis and spectroscopic properties of four newly synthesized dipyrazolo[3,4-b; 3',4'-e]pyridine (DPP) derivatives. The spectroscopic studies are supplemented by quantum-chemical calculations using DFT/TDDFT/PCM method at the B3LYP/6-31+G(d,p) level of theory. The optical absorption and fluorescence emission processes appear to be weakly dependent on attached side phenyl and/or methyl groups exhibiting in cyclohexane solution the first absorption band (00' transition) in the region of 386-401 nm and the fluorescence band (0'0 transition) in the range of 412-425 nm. The electroluminescence devices (OLEDs) with an active PVK layer doped by DPP dyes have been designed. All the devices exhibit deep blue electroluminescence with the emission maximum being rather weakly dependent on the type of the fluorescent dopant. The obtained results demonstrate that a series of newly synthesized DPP dyes may be considered as perspective blue fluorescent emitters for electroluminescent applications.

DFT/TDDFT study on the electronic structure and spectral properties of diphenyl azafluoranthene derivative.

Paper reports the DFT/TDDFT study on the electronic structure and spectral properties of the five-membered annulated diphenyl azafluoranthene derivative 1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-b]quinoline (DPIPQ) by means of polarizable continuum model (PCM) and Onsager reaction field approaches at the B3LYP/6-31+G(d,p) level of theory. The results of calculations are compared with the optical absorption and fluorescence spectra as well as with the cyclic voltammetry data. The DFT/TDDFT/PCM approaches exhibit rather good quantitative agreement regarding the spectral position of the first absorption band; the discrepancy between the experiment and theory is less than 0.06 eV (linear response approach) or 0.25 eV (state specific approach). As for the fluorescence emission the TDDFT/PCM calculations underestimate the transition energy on about of 0.7-0.8 eV. Such discrepancy should be attributed to insufficient quality of the TDDFT/PCM optimization in the excited state. Ignoring the geometrical relaxation in the excited state provides considerably better agreement between the experiment and theory; discrepancy is less than 0.1-0.22 eV depending on a solvent polarity. The dominant influence on the fluorescence emission results mainly from the solvent reorganization in the excited state whereas the solute relaxation is indeed weak and may be ignored.

Synthesis and spectroscopic study of several novel annulated azulene and azafluoranthene based derivatives.

A series of cyclized five-membered annulated azafluoranthene (AAF) and seven-membered annulated azulene (AA) derivatives have been synthesized and characterized by spectroscopic methods. The optical absorption and fluorescence spectra have been recorded in organic solvents of different polarity and analyzed within the semiempirical quantum chemical model PM3. In combination with the molecular dynamics simulations it properly reproduces the overall shape of the measured absorption spectra of both AA and AAF dyes including the strongest band in the region of 250-300 nm and the broad first absorption band above 400 nm. While the solvent polarity rises all the dyes exhibit the hypsochromic shift of the first absorption band and the bathochromic shift of the fluorescence band. Such opposite solvatochromic trends appear to be consistent with the Lippert-Mataga solvatochromic model. Compared to AA compounds, both AAF dyes reveal much stronger solvatochromic shift and broadening of the fluorescence band likewise the relative decrease in quantum yield on rising solvent polarity what may be an evidence for the intramolecular charge transfer mechanism being involved into the fluorescence emission. Depending on solvent polarity AA and AAF dyes emit light in the green-yellow range of the visible spectra what may be of interest for potential luminescent or electroluminescent applications.

UV-vis spectroscopy and semiempirical quantum chemical studies on methyl derivatives of annulated analogues of azafluoranthene and azulene dyes.

Paper reports the measured optical absorption and fluorescence spectra of 4-(2-chlorophenyl)-7-methyl-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline (MCPDPPQ), as well as 6-methyl-1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-b]quinoline (MDPIPQ) and 9-methyl-6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene (MPTNA) representing cyclized five- or seven-membered regioisomeric products of MCPDPPQ, respectively. The spectra has been recorded in solvents of different polarity and compared with the results of quantum chemical calculations performed by means of the semiempirical method PM3 in combination with molecular dynamics (MD) simulations. Cyclization of MCPDPPQ into MDPIPQ or MPTNA is accompanied by a significant red shift of the first optical absorption and fluorescence bands. While the solvent polarity rises all the dyes exhibit the blue shift of the first absorption band and the red shift of the fluorescence band. These trends have been reproduced within the semiempirical calculations in combination with the Lippert-Mataga dielectric polarization model and explained by specific orientations of the dipole moments in the ground and excited states. All dyes may be considered as candidates for the luminescent or electroluminescent applications. Depending on solvent polarity they emit light in the green-yellow range of the visible spectra.