Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 2, Issue 6, Pages 1594-1600Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am100050v
Keywords
mechanochromic; photochromic; spiropyran; ROP; DFT
Funding
- United States Department of Energy [DE-AC04-94-AL85000]
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A photochromic polymer exhibiting mechanochromic behavior is prepared by means of ring-opening polymerization (ROP) of epsilon-caprolactone by utilizing a difunctional indolinospiropyran as an initiator. The configuration of having the photochromic initiating species within the polymer backbone leads to a mechanochromic effect with deformation of polymer films leading to ring-opening of the Spiro C-O bond to form the colored merocyanine. Active stress monitoring by dynamic mechanical analysis (DMA) in tension mode was used to probe the effects of UV irradiation on polymer films held under constant strain. Irradiation with UV light induces a negative change in the polymer stress of approximately 50 kPa. Finally, a model of the mechanochromic effect was performed using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. A sharp increase in the relative molecular energy and the absorption wavelength as well as a drastic decrease in the spiro-oxygen atom charge occurred at a molecular elongation of >39%.
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