Spectroscopic study of lactonic rhodamine B immobilised on polytetrafluoroethylene porous film

Rhodamine B (RB) is frequently used in chemical sensors, where the sensing principle depends on its structural changes to lactone (L), zwitterion (Z), and cation (C) forms in response to the local environment. Compared to the Z- and C-forms, stabilising the L-form in matrices is difficult because of the required low environmental polarity. In this study, we report a simple and easy method to stabilise the L-form of RB on the surface of a polytetrafluoroethylene porous film (p-PTFE), in which the film is dipped in an ethanol solution containing RB and dried. This phenomenon was not observed on polyethylene film and cellulose filter paper in RB solutions. Furthermore, a chemical stability test for colourless RB/p-PTFE samples was conducted by exposing these samples to a humid environment. The test result indicated that, with an increase in the environmental humidity, the equilibrium shifted from the L-form to the Z-form of RB immobilised on the p-PTFE film.

Automated summary

The study presents a simple and easy method to stabilize the lactone (L) form of Rhodamine B (RB) on the surface of a polytetrafluoroethylene porous film. The results show that the L-form of RB can be stabilized in the porous film under low polarity environment, and this phenomenon is not observed on polyethylene film and cellulose filter paper. Furthermore, a chemical stability test demonstrates that the equilibrium of RB immobilized on the porous film shifts from the L-form to the zwitterion (Z) form with an increase in environmental humidity.