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

Abstract

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.

New stable colored complex of Al3+ with 1',3',3'‐trimethylspiro[2H‐1‐benzopyran‐2,2'‐indoline] (BIPS)

“…published data for SP in other solvents . Minor deviations observed are due to the specific solvation of SP by MeOH.…”

“…Our NMR data are consistent with published data for SP in other solvents. [38][39][40] Minor deviations observed are due to the specific solvation of SP by MeOH. 1 H NMR spectra of MC in SC are in accordance with the reported data for МСН +.…”

“…It is known that strong acids are able to protonate MC of SP and essentially stabilize it that way. [21][22][23] Therefore, it is of interest to compare the reactivity of Al 3+ and H + towards SP/MC. Despite its apparent simplicity, Al 3+ produces multiple hydro and aqua complexes in the presence of water and polynuclear Al III soluble compounds as well.…”

Design and Applications of Photoresponsive Hydrogels

“…This is an important consideration when evaluating possible side reactions. [70] The change from one isomer to the other is accompanied by a change in color, therefore pyranebased hydrogels possess inherent photochromic properties, which were lately shown to be tunable. These reactions are often reversible and produce no byproducts, which is desired for the design of photo responsive hydrogels.…”

“…The sensitive wavelengths for both groups can be tuned by varying the substituents. [70] The change from one isomer to the other is accompanied by a change in color, therefore pyranebased hydrogels possess inherent photochromic properties, which were lately shown to be tunable. [71,72] Their photochromic properties can be benefi cial in terms of easy indication and monitoring of the photo chemical reaction or for manufacturing sunglasslike hydrogel contact lenses.…”