From pirazoloquinolines to annulated analogues of azafluoranthene and azulene dyes: UV-VIS spectroscopy and quantum chemical study

Paper reports the measured optical absorption and fluorescence spectra of 4-(2-chlorophenyl)-1,3-diphenyl-1H-pyrazolo[3,4-6]quinoline (CPDPPQ), as well as 1,3-diphenyl-3H-indeno[1,2,3-de]pyrazolo[3,4-6]quinoline (DPIPQ) and 6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene (PTNA) representing cyclizated five-or seven-membered regioizomeric products of CPDPPQ, respectively. The spectra has been recorded in solvents of different polarity and compared with the results of quantum chemical calculations performed within the semiempirical method PM3. Cyclization of CPDPPQ into DPIPQ or PTNA 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 hypsochromic (blue) shift of the first absorption band and the bathochromic (red) shift of the fluorescence band. These trends have been reproduced within the semiempirical calculations and explained by nearly antiparallel orientation of the dipole moments in ground and excited states.