Chemical and Biomolecular Engineering - Research Publications
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ItemA nontoxic reversible thermochromic binary system via pi-pi stacking of sulfonephthaleins(Royal Society of Chemistry, 2019-08-14)The mechanisms of thermochromic materials are mostly based on Bragg reflection, surface plasmon absorption, molecular structure changes, conformational stretching or aggregation. Here, a simple class of dye–solvent binary systems with clear and reversible thermochromism around ambient temperatures is reported with an alternative mechanism. This system comprises commercially available sulfonephthaleins dissolved in liquid linear chain esters, acids or alcohols, which demonstrate colour changes at different temperatures when the solvents transition from solid to liquid states. The colour changing mechanism is based on π–π stacked aggregation or disaggregation of the sulfonephthalein dyes. Cell toxicity tests confirmed that the sulfonephthalein dyes are less toxic to NIH-3T3 cells than cyanidin chloride, which is the only reported nontoxic food dye affording thermochromism, while this is based on an alternative mechanism. With the choice of a nontoxic solvent, this binary system can form a nontoxic thermochromic material.
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ItemColor-Switchable Polar Polymeric Materials(American Chemical Society, 2019-08-14)Spiropyran is an important mechanophore, which has rarely been incorporated as a cross-linker in polar polymer matrices, limiting its applications in innovative mechanochromic devices. Here, three spiropyrans with two- or three-attachment positions were synthesized and covalently bonded in polar poly(hydroxyethyl acrylate) (PHEA), to achieve color-switchable materials, triggered by light and when swollen in water. The negative photochromism in the dark and mechanical activation by swelling in water were investigated. Measurements of negative photochromism were conducted in solution and cross-linked PHEA bulk polymers, with both showing color reversibility when stored in the dark or on exposure to visible light. The force of swelling in water was sufficient to induce the ring-opening reaction of spiropyran. It was found that tri-substituted spiropyran (SP3) was less influenced by the polar matrix but showed the fastest color activation during swelling. SP3 also showed accelerated ring opening to the colored state during the swelling process. Bleaching rates and color switchability were investigated under swollen and dehydrated conditions. The effect of cross-link density on the swelling activation was explored to better understand the interaction between the mechanophore and the polar environment. The results demonstrated that influences from both the polar environment and the mechanochromic nature of spiropyran had an impact on the absorption intensity, rate of change, and the decoloration rate of the materials. This study provides the opportunity to manipulate the properties of spiropyrans to afford materials with a range of color-switching properties under different stimuli.
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