Fig. 6.

Mechanochromic spiropyran based polymers that change color after stretching. a Spiropyran(SP) embedded poly(methyl acrylate) exhibits color change from yellow to red by ring opening reaction induced by applied strain. b Indolinospiropyran-poly(e-caprolactone) films turned to blue colored merocyanine form by mechanical force-induced bonds rearrangements. c Spiropyran embedded PDMS elastomer is patterned on a PDMS substrate and show a word “STOP” after a deformation

(Figure reproduced from a [50], Copyright 2009, Springer Nature; b [51], Copyright 2010, American Chemical Society; c [52], Copyright 2018)