Solvatochromic fluorescence in an immiscible two-phase system of alcohols and hydrophobic polymers: Distinction between light alcohol and water, ink printing

Abstract

A solvatochromic dye monomer with an allyl group (ASCD) was polymerized together with methyl methacrylate (MMA) or styrene (St) to obtain hydrophobic fluorescent polymers. The wettability of the polymers to alcohols was examined by monitoring the fluorescence (FL) changes over time. On the one hand, when the ASCD-incorporated poly MMA (PMMA) film was exposed to liquid alcohols, a remarkable red-shift occurred instantly in the FL emission spectra for light alcohols such as methanol, ethanol, and propanol whereas for heavier alcohols, a blue-shift occurred first and subsequently a red-shift occurred gradually. On the other hand, the ASCD-incorporated poly St (PSt) film exhibited less significant FL change upon contact with the light alcohols owing to the relatively higher hydrophobicity. In contrast to the case of alcohols, the polymer films exhibited no FL response to water even after prolonged exposure. Particularly, the ASCD-incorporated PSt film showed a reversible and reproducible FL change during the repeated methanol and water contact cycle, indicating a high potential for use as a sensor to discriminate between light alcohol and water. Moreover, when the ASCD-incorporated PMMA was ground mechanically and added to the alcohols, the nanoparticle powder was dispersed very well in the alcohols. When the colloidal solution was deposited onto a paper as an ink, high-resolution FL images were obtained on the surface of the paper.