Acid-base responsive multifunctional poly(formyl sulfide)s through a facile catalyst-free click polymerization of aldehyde-activated internal diynes and dithiols

Abstract

Acid-base equilibria play a critical role in biological processes and environmental systems. The development of innovative fluorescent polymeric materials to monitor acid-base equilibria is highly desirable. Herein, a novel catalyst-free click polymerization of aldehyde-activated internal diynes and dithiols was established, and exclusively Markovnikov poly(formyl sulfide)s (PFSs) with high molecular weights and moderate stereoregularity were produced in high yields. Because of the aromatic units and sulfur atoms in their main chains, these polymers possessed high refractive index values. By introducing the fluorene and aldehyde moieties, the resulting PFSs could act as a fluorescent sensor for sensitive hydrazine detection. Taking advantage of the reaction of the aldehyde group and hydrazine, imino-PFSs with remarkable and reversible fluorescence change through alternating fumigation with HCl and NH₃ were easily acquired and further applied in multicolor patterning, a rewritable material and quadruple-mode information encryption. Additionally, a test strip of protonated imino-polymer for the tracking of bioamines in situ generated from marine product spoilage was also demonstrated. Collectively, this work not only provides a powerful click polymerization to enrich the multiplicity of sulfur-containing materials, but also opens up enormous opportunities for these functional polysulfides in diverse applications.

Scheme 1. Catalyst-free click polymerization of aldehyde-activated internal diynes and dithiols.

Fig. 1. FT-IR spectra of 1a (A), 2a (B), model compound 3 (C) and P1a2a (D).

Fig. 2. ¹H NMR spectra of 1a (A), 2a (B), model compound 3 (C) and P1a2a (D) in CDCl₃. The solvent peaks are marked with asterisks.

Fig. 3. Wavelength-dependent refractive indices of the thin films of P1a2a–P1b2c.

Fig. 4. UV-vis absorption (A) and PL spectra (B) of P1a2aversus the concentration of hydrazine (0–350 equiv.) in THF solutions. Concentrations: 10⁻⁵ M, λ_ex = 350 nm. Insets: photographs of the probes before and after the reaction with hydrazine. (C) Plots of I/I₀ − 1 of P1a2aversus hydrazine concentration in THF solutions, where I = peak intensity and I₀ = peak intensity at hydrazine concentration = 0 M. (D) Emission intensity of P1a2a at 508 nm in the presence of hydrazine and its analogs (50 equiv. of each), λ_ex = 350 nm.

Fig. 5. (A) Absorption spectra and (C) cycling behavior (absorption at 530 nm) of imino-P1a2a film from the protonated to the deprotonated form by repeated fuming with HCl and NH₃ vapor. (B) PL spectra and (D) reversible switching of the emission between the jasper (emission at 535 nm) and salmon (emission at 645 nm) states after fuming with HCl vapor followed by NH₃ vapor. Inset photographs show the color and emission changes with the protonation and deprotonation processes.

Fig. 6. (A) Optimized structures of M and protonated analogues. (B) Calculated molecular conformation and orbital amplitude plots, along with the energy levels of the HOMOs and LUMOs of M and protonated analogues. (C) Schematic illustration of the acid and amine response mechanism via the protonation and deprotonation of imino-P1a2a.

Fig. 7. (A and B) Acid–base responsive patterns achieved by spraying imino-P1a2a solution onto filter paper. (C) Schematic illustration of writing and erasing patterns on filter paper using a mask with HCl and NH₃ vapor.

Fig. 8. Photographic images of dual-mode (A and B) and quadruple-mode (C) encryption models achieved by spraying responsive imino-P1a2a solution on filter paper. The dialog bubbles reveal the encrypted messages.

Fig. 9. Spoilage detection of marine products in sealed packages for 24 h at room temperature (experimental groups) and 4 °C (control groups) using protonated imino-P1a2a filter paper. Photographs were taken under normal illumination and UV irradiation.