Abstract

Abstract : Light can play important role in controlling biochemical process. Owing to their non-invasive nature, light can be utilized as a smart trigger to bring modification in biological activities of the substances. There are substances which show change in their chemical and physical properties when exposed to light radiation known as photochromic substances. The organic compounds which show photochromism include azobenzenes, diarylethenes, spiropyrans, spirooxazines, naphthopyrans, coumarins, phthalocyanine, fluorescein etc. During photochromism the molecules undergo cis-trans photoisomerism or electrocylic ring opening and closure hence showing two different absorption bands in UV-Visible light and dark. These photochromic molecules show application in molecular switches, sensors, photo imaging, fluorescence imaging of tissues and in biological studies as a diagnostic tools. The photochromic response can be triggered by using visible light, which is beneficial for medical applications. These photochromic dyes have found application in the pharmacotherapy, photodynamic therapy due to photo switchable properties. This review will focus on the application of photochromic dyes in the biomedical field not only as a diagnostic tool but also as a photoactivation controlled drug delivery system and also as a chemotherapeutic agent.