Synthesis of Novel Silica Encapsulated Spiropyran based Thermochromic Materials

Abstract

A series of novel spiropyrans were synthesized through the condensation of substituted 3,3-dimethyl-2-methyleneindoline with differentnitro substituted o-hydroxy aromatic aldehydes. Indoles were substituted initially with a variety of alkanes and esters moieties. The substituted 3,3-dimethyl-2-methyleneindoline were reacted with nitro substituted ohydroxy aromatic aldehydes to yield the respective spiropyrans. The synthesized novel spiropyrans were encapsulated in silica nano-shells to protect them from the effect of moisture and pH. The thermochromicbehavior of novel spiropyrans was studied by UVVisible spectroscopy. The thermally induced isomerizationof spiropyrans derivatives was carried out in water/ethanol mixture. The thermal isomerization of SP (colorless form) to MC (colored form) was discontinuous process as observed through a temperature change of 5-60 °C with the UV-Visible spectrometer. The absorption process occurs reversibly regardless of the heating /cooling sequence. The spiropyran derivatives therefore have a potential application for colorimetric temperature indication.