2-Ethylhexyl-2,4,5-trimethoxycinnamate and di-(2-ethylhexyl)-2,4,5-trimethoxybenzalmalonate as novel UVA filters

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A series of 2-ethylhexylmethoxy substituted cinnamates and benzalmalonates have been synthesized and characterized. 2-Ethylhexyl-2,4,5-trimethoxycinnamate (E8) and di-(2-ethylhexyl)-2,4,5-trimethoxybenzalmalonate (B8) show UVA absorption with high molar absorption coefficients (12000-14000 cm−1 M−1 at 350 nm). E8 undergoes trans to cis photoisomerization under UVA exposure causing the decrease in UV absorption efficiency. E8 is more photostable than butyl methoxydibenzoylmethane (BMDBM). For example, 41.64 J cm−2 UVA irradiation produces 20 ± 2% and 25 ± 2% loss in UV absorption for E8 and BMDBM, respectively. Similar irradiation produces no change in the UV absorption of B8. Both the oily liquid E8 and the yellow solid B8 can be dissolved in various organic solvents, ranging from methanol to hexane, various silicone fluids and 2-ethylhexyl-4-trimethoxycinnamate (EHMC, a widely used UVB filter). A liquid broadband filter comprising B8 and EHMC shows excellent photostability in both UVB and UVA regions.

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