Octupolar derivatives functionalized with superacceptor peripheral groups: synthesis and evaluation of the electron-withdrawing ability of potent unusual groups.

Novel tripodal derivatives with a triphenylamine core and that bear "superacidifiers" (i.e., fluorinated sulfoximinyl blocks) or novel sulfiliminyl moieties as peripheral groups were synthesized. These new chromophores show strong absorption in the near-UV region and emission in the visible region. The fluorinated sulfoximinyl moieties were found to behave as potent auxochromic and electron-withdrawing (EW) groups, thus leading to redshifted absorption and emission. These moieties promote a core-to-periphery intramolecular charge transfer (ctp-ICT) transition, the energy of which was found to be correlated to their EW strength. In this study, we provide evidence of a linear correlation between the Hammett constant (σ(p)) values and the electronic gap between the ground and first excited state of the three-branched derivatives. This in turn was used to derive σ(p) values of fluorinated sulfoximinyl moieties. These EWGs show unprecedentedly high σ(p) values, up to 1.45 relative to 0.8 for NO(2). Also, by using this method, the sulfiliminyl moiety was shown to exhibit similar EW strength as NO(2) , while promoting improved transparency and solubility. Finally, the superior EW strength of the fluorinated sulfoximine peripheral moieties was shown to induce significant enhancement of the two-photon absorption responses in the red near-IR region of the three-branched derivatives relative to similar octupoles that bear more usual strong EW groups. These characteristics (improved nonlinear responses or transparency) open new routes for the design of nonlinear optical (NLO) chromophores for optical limiting or electro-optical modulation. Such building blocks could also be of interest for optoelectronic applications, including the development of solar cells.