A comparative study of symmetrical and unsymmetrical trimethine cyanine dyes bearing benzoxazolyl and benzothiazolyl groups

Six symmetrical and unsymmetrical trimethine cyanine dyes bearing benzothiazolyl and benzoxazolyl groups were synthesized. Their linear optical properties were studied. It was found that the variation of hetero atoms play an important role in the spectral properties of the dyes. Sequential replacement of the oxygen atom by the sulfur atom resulted in a change in shade from yellow to purple. In order to understand the relationship between the molecular structures and the spectral properties of these dyes, theoretical calculations were made using the Gaussian programme. Key parameters related to absorption and emission spectra were reported and discussed.

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► Symmetrical and unsymmetrical trimethine cyanine dyes were synthesized.
► The absorption and emission bands were regularly changed by the variation of the heteroatom from oxygen to sulfur.
► DFT and TD-DFT calculations were used to explain the spectral properties.