Spiropyran Polymeric Microcapillary Coatings for Photodetection of Solvent Polarity

Fused silica microcapillaries were functionalized with spiropyran-polymer brushes using surface-initiated ring-opening metathesis polymerization. Based on the inherited spiropyran properties, the functionalized capillaries were successfully used to photoidentify solvents of different polarity when passing through the microcapillary in continuous flow. In the present study, six different solvents (toluene, tetrahydrofuran, acetone, acetonitrile, ethanol, and methanol) can be easily detected while passing through the modified microcapillary by simply irradiating a portion of it with UV light (365 nm). This converts the closed spiropyran moiety to the open merocyanine form, and as a consequence, the microcapillary gains a distinct color and spectral response depending on the polarity of the solvent. The rate of ring-opening of the spiropyran-polymer brushes coatings has been determined in situ in the presence of different solvents, showing that the coloration rate is also influenced by the solvent polarity and therefore can be used as an additional parameter for solvent sensing

Photoswitchable Layer-by-Layer Coatings Based on Photochromic Polynorbornenes Bearing Spiropyran Side Groups

Herein, we present the synthesis of linear photochromic norbornene polymers bearing spiropyran side groups (poly­(SP-R)) and their assembly into layer-by-layer (LbL) films on glass substrates when converted to poly­(MC-R) under UV irradiation. The LbL films were composed of bilayers of poly­(allylamine hydrochloride) (PAH) and poly­(MC-R), forming (PAH/poly­(MC-R))_<i>n</i> coatings. The merocyanine (MC) form presents a significant absorption band in the visible spectral region, which allowed tracking of the LbL deposition process by UV–vis spectroscopy, which showed a linear increase of the characteristic MC absorbance band with increasing number of bilayers. The thickness and morphology of the (PAH/poly­(MC-R))_<i>n</i> films were characterized by ellipsometry and scanning electron microscopy, respectively, with a height of ∼27.5 nm for the first bilayer and an overall height of ∼165 nm for the (PAH/poly­(MC-R))₅ multilayer film. Prolonged white light irradiation (22 h) resulted in a gradual decrease of the MC band by 90.4 ± 2.9% relative to the baseline, indicating the potential application of these films as coatings for photocontrolled delivery systems