Solvatochromism and estimation of ground and excited state dipole moments of 6-aminoquinoline

The spectral behaviour of 6AQ was investigated using fluorescence spectroscopy in several polar and nonpolar solvents. Both the absorption and fluorescence spectra displayed solvatochromism. The Stokes shift increased significantly with increasing solvent polarity and signifies a more polar excited state with pos- sible change in the excited state (ES) geometry. The involvement of pi -> pi* transition was observed. The ground state (GS) and excited state (ES) dipole moments were determined by the solvatochromic shift method using Bilot-Kawaski, Lippert-Mataga, Kawski-Chamma-Viallet, and Reichardt equations. The experimental value of GS dipole moment matches closely with the theoretical value computed using DFT/B3LYP/6-311G(d,p). The ES dipole moment is higher than the GS dipole moment. Besides, the solvatochromic study reveals that the ES of 6AQ is more polarized than the GS due to intramolecular charge transfer (ICT), possibly aided by a change in the geometry of the molecule in the ES. The influence of the non-specific and specific interactions in the photophysical properties of the titled molecule was analyzed using the Catalan scale. The study shows that 6AQ has reasonable band-gap energy and good CIE chromaticity coordinate in the blue region close to the national television standard committee system (NTSC) for the ideal blue CIE coordinate. Therefore, future research into 6AQ as a source of lighte-mitting diodes and fluorescent sensors may have potential applications in the field of optoelectronics. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the spectral behavior of 6AQ in different solvents, showing solvatochromism with increasing Stokes shift and a more polar excited state possibly due to a change in geometry and involvement of pi -> pi* transition. The dipole moments of the ground state and excited state were determined, with the excited state having a higher dipole moment possibly due to intramolecular charge transfer. The molecule exhibited reasonable band-gap energy and good blue CIE coordinates, suggesting potential applications in optoelectronics.