Spiropyran-Containing Poly(L-Glutamic Acid). Photochromic and Conformational Behaviour in Acid Conditions

Poly(L-glutamic acid) containing spiropyran groups in the side chains was found to exhibit reverse photochromism in hexafluoro-2-propanol in the presence of trifluoroacetic acid, but the polypeptide conformation was not affected by the photoisomerization of the photochromic units. When appropriate amounts of methanol were added as a cosolvent, the system responded to light giving reversible coil ← α-helix transitions whose extent depended on methanol concentration.