Transparent chromic polymer films based on natural anthocyanins are promising responsive materials, but their performance is often limited by chromophore instability, deposition-dependent heterogeneity, and poorly controlled transport kinetics. In this work, anthocyanin–poly(vinyl alcohol) (PVA) films were fabricated by spin coating and drop casting to clarify how processing-induced thickness differences affect optical density, vapor-induced chromic response, and light-aging behavior. By varying RedC dye loading from 1 to 2 wt% and changing the deposition method, film thickness was tuned from approximately 10–120 μm. Spin-coated films exhibited rapid chromic activation under acidic vapors, whereas thicker drop-cast films showed slower response, consistent with a longer vapor diffusion path through the polymer layer. Thickness-normalized absorbance analysis indicated that the stronger absorbance of drop-cast films mainly arises from optical path-length effects, although residual differences in attenuation per unit thickness remained detectable. Photostability experiments performed on spin-coated films showed loading-dependent visible chromophore retention, with the 2 wt% formulation retaining more than 90% of its visible absorbance after three months of accelerated irradiation. Overall, the results identify film thickness as a key structural parameter linking processing, optical density, and vapor-response kinetics. • Spin coating and drop casting tune RedC@PVA film thickness from 10 to 120 μm. • Thickness controls optical density through optical path-length effects. • Thin spin-coated films show faster acidic-vapor chromic activation. • 2 wt% spin-coated films retain > 90% visible absorbance after light aging. • Processing control links film thickness, vapor response, and chromophore retention.
Desiderio et al. (Wed,) studied this question.