Photoluminescence of methoxy and carboethoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline: Experiment and quantum-chemical simulations

The optical absorption and photoluminescence are studied in the newly synthesized methoxy (MO) and carboethoxy (CE) diphenyl-pirazoloquinoline (DPPQ)-derivatives: 6MO[DPPQ], 6MO1pMO[DPPQ], 6MO13pMO[DPPQ] and 6CE[DPPQ]. The photoemission spectra are recorded in organic solvents of different polarities and found to be highly solvatochromic. 6MO[DPPQ] and 6CE[DPPQ] show broad emission bands shifted to the red with the increase of solvent polarity, whereas the phenyl-methoxy derivatives 6MO1pMO[DPPQ] and 6MO13pMO[DPPQ] exhibit the reverse solvatochromism. The measured spectra are compared with the quantum-chemical calculations performed by means of the semiempirical methods (AM1 or PM3) in combination with geometries taken from equilibrium molecular conformation in vacuo ( T = 0  K) or molecular dynamic simulations ( T = 300  K). It is expected that conformational changes related to the phenyl-methoxy moieties play an important role in the reverse solvatochronism. The methoxy and carboethoxy [DPPQ]-derivatives emit light in the blue and green spectral range (quantum yield 0.6–0.8%).