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. 2022 Mar 2;9(3):211385.
doi: 10.1098/rsos.211385. eCollection 2022 Mar.

Synthesis of novel silica encapsulated spiropyran-based thermochromic materials

Anila Iqbal  1 , Ghazala Iqbal  2 , Muhammad Naveed Umar  3 , Haroon Ur Rashid  4 , Sher Wali Khan  5
Affiliations

Synthesis of novel silica encapsulated spiropyran-based thermochromic materials

Anila Iqbal et al. R Soc Open Sci. .

Abstract

A series of novel spiropyrans were synthesized through the condensation of substituted 3,3-dimethyl-2-methyleneindoline with different nitro-substituted o-hydroxy aromatic aldehydes. Indoles were initially substituted with a variety of alkanes and esters moieties. The substituted 3,3-dimethyl-2-methyleneindoline was then reacted with nitro-substituted o-hydroxy 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 thermochromic behaviour of novel spiropyrans was studied by UV-visible spectroscopy. The thermally induced isomerization of spiropyran derivatives was carried out in a water/ethanol mixture. The thermal isomerization of spiro-heterocyclic (colourless form) to merocyanine (MC) (coloured form) was a discontinuous process and was observed in a temperature range of 5-60°C via 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.

Keywords: colorimetric; spiro-heterocycles; spiropyran; thermochromism.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Figure 1.
Figure 1.
Transformation of spiropyran.
Figure 2.
Figure 2.
Synthetic scheme for the synthesis of spiropyrans and their encapsulation.
Figure 3.
Figure 3.
XRD patterns of hollow silica mesospheres and dye encapsulated mesospheres.
Figure 4.
Figure 4.
SEM images of various encapsulated spiropyrans mesospheres. (a) SEM of SP-3E at a magnification of 30 000. (b) SEM of SP-3E at a magnification of 15 000. (c) SEM of SP-8E at a magnification of 30 000. (d) SEM of SP-8E at a magnification of 15 000. (e) SEM of SP-12E at a magnification of 30 000. (f) SEM of SP-12E at a magnification of 15 000.
Figure 5.
Figure 5.
Temperature-dependent change in absorption spectra of SP-8 (e50 μM) measured in water-MeOH (1 : 1 v/v).
See this image and copyright information in PMC

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