One‐Pot Synthesis and Photophysical Studies of Styryl‐Based Benzo[f]pyrazolo[3,4‐b]quinoline and Indeno[2,1‐b]pyrazolo[4,3‐e]pyridines

Abstract

A new family of extended π‐conjugated dihydrobenzopyrazoloquinoline (DBPQ) and dihydroindenopyrazolopyridine (DIPP) molecules were synthesized, and their photophysical and electrochemical properties were studied. The DBPQ derivatives showed significantly higher molar absorption coefficients, and their absorption and emission wavelengths were red‐shifted with respect to those of the corresponding DIPP derivatives in chloroform solution. Dyes with no substitution and methoxy, nitro, and fluoro‐substituted derivatives showed poor dependence on solvent polarity. At the same time, DBPQ and DIPP derivatives with dimethylamino groups exhibited strong solvatochromism in the emission spectra. Due to the presence of a vinyl link with a cylindrical π‐cloud on the donor (dimethylamino group) molecule, they showed efficient positive solvatochromism with high quantum yields on increasing solvent polarity from non‐polar to polar solvents. Aggregation‐induced emission (AIE) properties were also investigated. AIE studies show that the emission of DBPQ and DIPP derivatives in the presence of THF/H2O mixture increased due to aggregation. However, DBPQ and DIPP derivatives were still strongly emissive in the solid state. Dimethylamino substituted derivatives exhibited acidochromism, which was caused by the addition of TFA and pTsA leading to prominent red‐shifts in the emission spectra owing to the protonation at the pyridine segment.