Synthesis, photochromic properties, and bioactivity of spiropyrans with electron-donating/withdrawing substituents on indoline and [2 <i>H</i> ]-chromene rings

Photochromic molecules from the spiropyran family are renowned for their ability to undergo light-induced interconversion between a colorless spiro form and a colored merocyanine form. The photoswitching behavior of various spiropyrans has been explored earlier but the influence of electron-donating and electron-withdrawing groups on the indoline and [2<i>H</i>]-chromene rings remains unexplored. In this work, we synthesized four distinct photochromic spiropyran molecules featuring all possible combinations of electronic effects. Their photoswitching activity and switching kinetics were systematically analyzed using spectroscopic and kinetic techniques. Furthermore, the antibacterial properties of these spiropyran derivatives were evaluated to uncover potential structure-activity relationships. This study provides important insights into the design of spiropyrans with customized photochromic properties and associated bioactivity.