Synthesis and application of poly methyl indole-4-carboxylate with blue light blocking properties

Abstract

Blue light hazards have garnered increasing attention owing to the popularity of displays. Although melanin on the retina acts as a blue light barrier, overexposure to blue light increases the risk of visual damage. A class of methyl indole-n-carboxylate oligomers (O-MInC, n = 3, 4, 5, 6, and 7) was synthesized through solid-phase oxidative polymerization. Based on the experimental characterizations, including time-of-flight mass spectrometry, infrared spectroscopy, and density functional theory calculations of the average local ionization energy, we proposed a mechanism for the oxidative polymerization of methyl indole-4-carboxylate (MI4C). Methyl indole-4-carboxylate oligomer (O-MI4C) is composed of cyclic oligomers containing large conjugated structures that are generated by the repetition of electron deprivation, radical coupling, and dehydrogenation reactions. O-MI4C exhibits the best blue light absorption among its allotropes substituted at different positions with a cut-off absorption wavelength of 530 nm. Finally, O-MI4C was added to polymethylmethacrylate (PMMA) and Columbia resin 39 (CR-39) flakes through in situ polymerization to investigate the behavior of blue light blocking. The PMMA/O-MI4C (0.01 wt%) and CR-39/O-MI4C (0.02 wt%) can block 25% and 35% of blue light; however, they have no significant effect on green and orange lights.