Third-order nonlinear optical properties of unsymmetric pentamethine cyanine dyes possessing benzoxazolyl and benzothiazolyl groups

A series of unsymmetric pentamethine cyanine dyes featuring benzoxazolyl and benzothiazolyl groups were synthesized, the structures were characterized by 1H NMR, UV–vis absorption spectroscopy and mass spectrometry. The dyes with different anions such as chloride, tetraphenylborate and tetra(4-fluorophenyl)borate were also obtained and their solubility can be changed by the choice of the anion part. The third-order nonlinear optical properties were measured by the Z-scan technique with a picosecond laser beam at 532 nm in DMF solution. The third-order nonlinear optical susceptibilities χ(3) and the second-order hyperpolarizabilities γ' were obtained. The results reveal that these dyes exhibit strong reverse saturable absorption and nonlinear refraction.

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► A series of unsymmetric pentamethine cyanine dyes were synthesized.
► Dyes with B(C6H4F)4− anion part possess favorable solubility.
► The third-order nonlinear optical (NLO) properties of dyes were reported.