Significant impact of 3-positioned substituent on the fluorescent properties of 5-hydroxyisoquinolones

Fluorescent properties of 5-hydroxyisoquinolone-3,4,6,7,8- pentacarboxylates and their 4,6,7,8-tetracarboxylate analogs lacking a 3-positioned electron-withdrawing ester group differ substantially. The presence of an electron-withdrawing group at position 3 in the 5-hydroxyisoquinolone system was found crucial for their vibrational relaxation in the anionic forms, which highlights the importance of substitution pattern providing valuable insights for future research in this area.