M. Bertoldo et al. / Carbohydrate Polymers 85 (2011) 401–407
407
The new chitosan based material with covalently bound
spiropyran groups showed an interesting photochromic response.
Indeed, after UV light irradiation, the colorless material became
intensely colored either in Et2O suspension or solid film due to the
conversion of the spiropyran in the merocyanine form. The photo-
excited merocyanine form lived more than 24 h as suspension in
diethyl ether and more than two months as dry film at room tem-
perature. By contrast, the unbound spiropyran in ethanol or diethyl
ether bleached in few minutes. This very low thermal recovery of
the photo-generated open merocyanine form in the solid state can
be ascribed to chemical and physical stabilization of the open mero-
cyanine by mainly nonbonded environmental effects derived by the
embedment of the chromophore into the chitosan material. These
findings indicate a very well controlled route to provide a polysac-
charide, in particular chitosan, with a specific photoresponse to
light irradiation which is affected and modified to large extent by
chromophore–biomacromolecule nonbonded interaction.
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