Reversible light-induced solubility of disperse red 1 dye in a hydroxypropyl cellulose matrix

We present results on reversible light-induced solubility of disperse red 1 (DR1) dye in a hydroxypropyl cellulose (HPC) matrix. The samples were prepared by dissolution of both DR1 and HPC in acetone and left to dry overnight in air to form not totally uniform red coatings. It is observed that both heating and illumination of the samples with visible light promote the appearance of a dark red coloration inside the heated or illuminated regions. This new phenomenon is attributed to a dissolution of dye and/or disruption of DR1 aggregates. It is confirmed by visible light and FTIR spectroscopies. UV-Vis spectra evidence disappearance of a band at 400 nm, which is attributed to DR1 aggregates, upon illumination of the samples with visible light. FTIR spectra show new bands at 1600, 1508, and 1342 cm(-1) that were assigned to symmetric and asymmetric stretching modes of NO2 of the dissolved DR1. Results evidence a dye solubilization process throughout repeated trans-cis isomery induced by visible light. This process is also a new feature of the light induced molecular movements of azo-dyes and may be used in future for the photo-command of polymer properties and/or light storage. This work opens new perspectives to use natural polymers and composites in photonic applications. It also reveals the strong potential of azo-materials as light powered molecular motors.