The halogens in focus: the case of spiropyrans with an elongated conjugation chain

Spiropyrans are a promising class of organic photochromic compounds that are currently of great interest, especially in the fields of molecular electronics, chemosensing, photopharmacology and theranostics. One of the key challenges hindering the widespread practical application of these compounds involves enhancing the stability of the active form and shifting its absorption maximum toward the far-red or even near-infrared (NIR) region of the spectrum. In this study, a series of new spiropyran derivatives with elongated conjugation chains and halogen atoms was obtained. These derivatives exhibit exceptional spectral and kinetic properties, such as NIR-absorption and emission, as well as an extended lifetime of the active form. Of particular interest is the complex case of multiple electronic effects observed in these compounds, which was extensively studied by theoretical modeling. Additionally, we conducted initial photodriven toxicity studies of target compounds using bacterial lux-biosensors, which confirmed their potential as theranostic agents. The results obtained provide valuable insights into the structural factors that determine the properties of spiropyrans, contributing to the rational design of photochromic compounds for various applications.