New insights into the excited state of an A-D-A quadrupolar molecule strongly hydrogen bonded to molecules of methanol and hexafluoro isopropanol

Abstract

In this work, we carried out density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations to study the hydrogen-bonding dynamics of 2,5-bis(4- cyanophenyl)-1,4-bis(4-methylphenyl)-1,4-dihydropyrrolo [3,2-b] pyrrole (ADA) in strongly H-bonding liquids. ADA, is a quadrupolar A–π–D–π–A type molecule (A-D-A), where A and D are electron-accepting and electron-donating moieties. Our theoretical results are consistent with previously reported experimental data. According to our computations, the CN···HO intermolecular hydrogen bonds formed between ADA and methanol, and between ADA and hexafluoro isopropanol are tremendously strengthened in the electronically excited-state upon the photoexcitation of their hydrogen-bonded complexes. The enhancement of the intermolecular hydrogen bond motives the dispersion of holes and electrons and the asymmetry of the ADA molecules in strongly H-bonded liquids, which promotes the red shift of the CN stretching vibration and the changes in the form of the solvent ADA around. The degree of asymmetry harm is associated to the solvent proton-donating ability and the phenomenon of increased asymmetry can be prolonged to the application of different dye molecules. The lookup will help experimenters develop different dyes with excellent performance.