We report on a new vapochromic system suitable for sensing volatile organic compounds (VOCs) based on\udpolymer films doped with 4-(diphenylamino)phthalonitrile (DPAP), a fluorescent molecular rotor sensitive\udto both solvent polarity and viscosity. Poly(methyl methacrylate) (PMMA) and polycarbonate (PC) films\udcontaining small amounts of DPAP (#0.1 wt%) were prepared and exposed to saturated atmospheres of\uddifferent VOCs. DPAP/PMMA films show a good and reversible vapochromism when exposed to VOCs\udwith high polarity index and favourable interaction with polymer matrices such as THF, CHCl3, and\udacetonitrile. Analogously, DPAP/PC films exposed to polar and highly polymer-interacting solvents, that\udis, toluene, THF, and CHCl3, show a gradual decrease and red-shift of the emission. In contrast to DPAP/\udPMMA films, an unexpected increase and further red-shift of fluorescence are observed at longer\udexposure times as a consequence of an irreversible, solvent-induced crystallization process of PC. The\udvapochromism of DPAP-doped films is rationalized on the basis of alterations of the rotor intramolecular\udmotion and polarity effects stemming from the environment, which, in concert, influence the\uddeactivation pathways of the DPAP intramolecular charge transfer state. Overall, the present results\udsupport the use of DPAP-enriched plastic films as a new chromogenic material suitable for the detection\udof VOCs.
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