Synthesis and spectral properties of near-IR polymethine dyes derived from tris(2,2,3,3,4,4,5,5-octafluoropentyl)-9H-fluorene-2,4,7-trisulfonate

- Anionic polymethine dyes based on trisubstituted fluorene have been synthesized.
- They demonstrate strong and selective near-IR absorption.
- The new dyes have been observed to form contact ion pairs in low-polarity media.
- TDDFT-calculated spectra of the dyes correlate well with the experimental results.

A vinylogous series of anionic polymethine (cyanine) dyes has been synthesized based on tris(2,2,3,3,4,4,5,5-octafluoropentyl)-9H-fluorene-2,4,7-trisulfonate. It has been found that their longest-wavelength and most intense electronic transition has the polymethinic origin, unlike the analogous polynitrofluorene dyes. As established, the corresponding absorption band, in contrast to that of classical cyanines, remains quite intense and narrow in the near-IR spectral region even in highly polar solvents. The nature of electronic transitions and relevant molecular orbitals as well as excitation-induced electron density redistributions have been studied by the DFT and TDDFT methods at the CAM-B3LYP/6-31G(d,p) level.

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