The high stability of merocyanine and significant slow fading speed of naphthopyran in layer-by-layer assembled films via hydrogen bonding

A photochromic polymer film has been fabricated by the layer-by-layer (LBL) self-assembly through alternating the deposition of poly(acrylic acid) bearing a naphthopyran copolymer and poly(4-vinylpyridine) in an organic solvent. The multilayer assembly process is monitored via UV-vis spectroscopy by measuring the increase in absorbance at 380 nm, and the results reveal that the multilayer films grow in a uniform way in each deposition. Atomic force microscopy (AFM) images prove that the surface of the film was relatively smooth. The photochromic properties of the naphthopyran in the LBL films are investigated and the kinetic results confirm that the colored merocyanine in the LBL films show a significant slow fading speed (critical T1/2 decoloration time increased to 64 min in the 3-bilayer film) and are more stable than those in previous reports.