Comparative Evaluation of Substituent Effect on the Photochromic Properties of Spiropyrans and Spirooxazines.

Spiropyrans and spirooxazines represent an important class of photochromic compounds with a wide variety of applications. In order to effectively utilize and design these photoswitches it is desirable to understand how the substituents affect photochromic properties, and how the different structural motifs compare under identical conditions. In this work a small library of photoswitches was synthesized in order to comparatively evaluate the effect of substituent modifications and structure on photochromism. The library was designed to modify positions that were believed to have the greatest effect on C-O bond lability and therefore the photochromic properties. Herein we report a comparative analysis of the UV and visible light responses of 30 spiropyrans, spiroindolinonaphthopyrans, and spirooxazines. The influence of gadolinium(III) binding was also investigated on the library of compounds to determine its effect on photoswitching. Both assays demonstrated different trends in substituent and structural requirements for optimal photochromism.

Antioxidant Sensing by Spiropyrans: Substituent Effects and NMR Spectroscopic Studies.

The development of stimuli-responsive small molecules for probing biologically active antioxidants such as glutathione (GSH) has important ramifications in the detection of oxidative stress. An ideal sensor for biological applications should exhibit sufficient sensitivity and selectivity for detection at physiological concentrations and be reversible to allow continuous and dynamic monitoring of antioxidant levels. Designing a suitable sensor thus requires a detailed understanding of activation properties and mechanism of action. In this work, we report a new set of GSH-responsive spiropyrans and demonstrate how changes in the electronic structure of spiropyrans influence GSH sensing with high specificity versus other structurally similar and biologically relevant redox-active molecules. The sensitivity, selectivity, kinetics, binding constant, and reversibility of GSH-responsive-substituted spiropyrans were investigated using UV-vis spectroscopy and laser irradiation experiments. Detailed studies of the mechanism of interaction between spiropyrans with GSH were investigated using NMR spectroscopy. Understanding how electronic effects impact the sensing ability of spiropyrans toward antioxidants and elucidating the mechanism of the spiropyran-GSH interaction will facilitate the design of more effective sensors for detection of antioxidants in vivo.