Photochromic property of anionic spiropyran with sulfonate-substituted indoline moiety

For fabricating photoresponsive multifunctional materials, we have developed the potassium salt of a new anionic spiropyran, 1′,3′, 3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline] -5′-sulfonate (1^-), with the sulfonate group present on the indoline moiety and whose crystal structure was revealed by single-crystal X-ray diffraction analysis. The photochromism of 1·K was demonstrated at room temperature in the KBr-diluted state, as well as in solution. The protonated spiropyran 1H shows negative photochromism.