Selective employment of electronic effects of the pentafluorosulfanyl group across linear and tripodal push–pull chromophores with two-photon absorption

Abstract

Twelve model amino-based linear D–π–A and tripodal D–(π–A)₃ chromophores bearing electron-withdrawing SF₅-group(s) at different peripheral positions were designed and prepared in a straightforward way. The influence of the position and the number of SF₅-groups was studied with the aid of single crystal X-ray analysis, thermal and electrochemical measurements, (non)linear steady-state and time resolved spectroscopies, and DFT calculations. Significant property tuning can be achieved when modulating the number and position of the (peripheral) SF₅-group(s), e.g. increase of the thermal robustness from 300 to 420 °C, the HOMO–LUMO gap is tuned through an exclusive manipulation of the LUMO, and the absorption/emission maxima can be red-shifted. The para-positioning allowing their hyperconjugation and the increasing number of the appended SF₅-groups along with a polar environment support the intramolecular charge-transfer and open a non-radiative deexcitation channel, while the two-photon absorption cross-section is generally enhanced for the para-substituted octupolar chromophores. Thus, properly placing the SF₅-group(s) along the π-conjugated backbone allows a principal tuning of the push–pull chromophore fundamental function(s).