Synthesis and fluorescence behavior of photoactive polyhydroquinoline derivatives: A combined experimental and DFT study

A series of biologically important substituted polyhydroquinoline derivatives were synthesized by one-pot protocol using palladium nanoparticles as an efficient catalyst. Photophysical behavior of the synthesized systems was monitored using steady state and time-resolved fluorescence techniques in a series of neat and mixed solvents as well as by time dependent density functional theory (TDDFT). An additional large Stokes-shifted fluorescence band is observed in N,N′-dimethylamino derivative over the nitro and/or methoxy substituted system and is believed to be originated due to the formation of an intramolecular charge transfer (ICT) state. The intensity of this additional fluorescence band decreases considerably in polar protic environment and also in presence of trace amount of acid, confirming the involvement of nitrogen lone-pair of electrons towards the formation of the charge transfer state.

The additional intramolecular charge transfer (ICT) fluorescence band in III appears due to the formation of pro-ICT structure only in the excited state.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of polyhydroquinoline derivatives using Pd(0) nanoparticles.
► Photophysical characterization by time-resolved fluorescence and TDDFT calculation.
► Additional ICT fluorescence in dimethylamino substituted compound only.
► Formation of ICT structure is possibly due to 1,3-H migration in the excited state.
► Correlation of ICT emission parameters and decay with solvent polarity parameter.