Preparation and properties of photochromic bacterial cellulose nanofibrous membranes

The photochromic bacterial cellulose (BC) nanofibrous membranes containing 1',3',3'-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2'-indoline) (NO2SP) were successfully prepared by surface modification of BC nanofibers with spiropyran photochromes, and their physical and photochromic properties were characterized. The FTIR spectra indicated the interaction between BC and NO2SP which leads to the uniform dispersion of NO2SP in the nanofibrous membrane. SEM results demonstrated that the introduction of NO2SP maintains the nanofibrous network structure of BC. UV/vis spectrometry of the resulting BC-NO2SP revealed that the membranes show reversible photochromic property by changing their color from colorless to pink forming a merocyanine structure upon UV irradiation, and returning back again to colorless spiropyran structure by visible light. The contact angle of the BC-NO2SP with water was found to be reversibly regulated due to the reversible isomerization of the spiropyran moieties in BC-NO2SP. The result indicates that the surface modification with spiropyran photochromes expands new applications of BC nanofibers and such photochromic nanofibers with excellent photosensitivity have great potentials for sensitive displays, biosensors and other optical devices.