Light-controlled receptors for environmentally and biologically relevant anions

[Display omitted] •The advancement in anion sensors developed on photochromic platforms has been highlighted.•The photochromic molecules show excellent sensitivity and selectivity for anions.•Photochromic molecule anion complexes showing a variety of outputs have been summarized.•The photosensitive nature of the anion complex allows the light-controlled release of the anion. In the past few decades monitoring the concentration of anions has received much interest due to their role in driving biological processes at low concentrations and toxicity at elevated levels. Sensors based on photochromic molecules with positively charged spiro carbon have been used often to detect the presence of toxic and biologically important anions. Moreover, photochromic molecules can be easily modified to generate anion coordination sites. The alteration in the structure of photochromic molecules induced by anion causes a change in their optical properties, which may be used for monitoring the presence of anionic pollutants. Therefore, the review is focused on various design strategies, the effect of substituents, and the mechanism of sensing anions by sensors based on photochromic molecules reported recently in the literature. It is hoped that the review may further accelerate the development of improved anion sensors for monitoring their concentration in biological and environmental applications.