Ultrafast nonlinear optical properties of cyclohexenone carboxylate derivatives and their application as organic saturable absorbers

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In order to understand the phenomenon of small molecule organic saturable absorbers, the carboxylate compounds ethyl-6-(4-benzyloxyphenyl)-4-phenyl-2-oxycyclohex-3-ene-1-carboxylate (CAR I), ethyl-6-(4-benzyloxyphenyl)-4-(4-methylphenyl)-2-oxycyclohex-3-ene-1-carboxylate (CAR II) and ethyl-6-(4-benzyloxyphenyl)-4-(4-bromophenyl)-2-oxycyclohex-3-ene-1-carboxylate (CAR III) compounds were synthesized by Michael addition reaction of chalcones with ethylacetoacetate. The UV absorption λmax values of CAR I, CAR II, CAR III were found to be 284, 296, 292 nm respectively. Similarly, the optical band gap of these carboxylate compounds were calculated using HOMO-LUMO were 3.87, 3.89, 3.8 eV correspondingly. The nonlinear absorption (NLA) coefficient, β value of these compounds were found as −3.89 × 10−12, −4.23 × 10−12, −3.71 × 10−12 m/W and nonlinear refractive (NLR) index, n2 were determined as 16.83 × 10−19, 13.87 × 10−19, 6.11 × 10−19 m2/W. Third order nonlinear susceptibility, χ(3) were found as 12.29 × 10−13, 7.8 × 10−13, 4.16 × 10−13esu. These cyclohexene carboxylate derivatives showed saturable absorption owing to higher optical band gaps. The nonlinear refractive index values have shown that these carboxylate compounds were focusing in nature. The CAR I has highest nonlinear refractive index of 16.83 × 10−19 m2/W and nonlinear susceptibility of 12.29 × 10−13esu compared to CAR II and CAR III indicating substitution by either electron donor or accepter reduce the susceptibilities.