Optical absorption and fluorescence spectra of novel annulated analogues of azafluoranthene and azulene dyes

Paper reports optical absorption and fluorescence spectra as well as basic photophysical characteristics of newly synthesized 1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-b]quinoline (DPIPQ) and 6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene (PTNA) dyes being recorded in organic solvents of different polarity. The experimental results are compared with the quantum chemical calculations performed within the semiempirical method PM3. While the solvent polarity changes from cyclohexane to acetonitrile both dyes exhibit the hypsochromic (blue) shift of the absorption spectra and the bathochromic (red) shift of the fluorescence spectra. This fact is found to be consistent with the Lippert–Mataga solvatochromic model and is explained by a specific orientation of the ground and excited state dipole moments. Quantitative evaluations of the solvatochromic shifts give quite well agreement with the experimental data only for optical absorption spectra of both dyes. In the case of the fluorescence spectra the experiment suggests much larger dipole moment of the excited state comparing to the one which follows from the semiempirical calculations. Corresponding discrepancy is especially strong for DPIPQ dye and is assumed to be related with an enhanced mixing of the lowest LE state with the lowest ICT states due to lowering of their energies in a polar solvent environment. Both dyes reveal substantial quantum yield thus 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.