Proximal effects of ultraviolet light absorbers and polymer matrix in the photostability of β-carotene

β-Carotene was used as a probe to investigate the protection offered by 2-ethylhexyl 4-methoxycinnamate, a photostabilizer, upon ultraviolet-A photodegradation. β-Carotene and 2-ethylhexyl 4-methoxycinnamate were arranged in two distinct macroscopic configurations (core/shell and homogenous) in solution with tandem and single cuvettes. 2-Ethylhexyl 4-methoxycinnamate was also combined with poly(methyl methacrylate) in solution to investigate the protective synergy between the photostabilizer and the polymer matrix. The choice of configuration played a more dominant role than the concentration of 2-ethylhexyl 4-methoxycinnamate in the degradation of β-carotene, with β-carotene remaining more stable in the homogeneous configuration. Changing configurations yielded different proximities of 2-ethylhexyl 4-methoxycinnamate to β-carotene; closing the proximity increased the potential close interactions (<1 nm) where transfer of excited state energy from β-carotene to 2-ethylhexyl 4-methoxycinnamate could occur resulting in increased photostability. The addition of poly(methyl methacrylate) had a negligible impact on the decay of β-carotene in both configurations.

► The proximity of β-carotene and 2-ethylhexyl 4-methoxycinnamate plays a large role in photostability. ► There is a threshold of separation of 15 nm between β-carotene and 2-ethylhexyl 4-methoxycinnamate. ► Greater photostability is achieved below the threshold distance.