Synthesis and investigation of the optical and electrochemical properties of deep blue light-emitting poly[fluorene-2,7-diyl-co-dibenzothiophene-S,S-dioxide-4,6-diyl]s

Abstract

We synthesized a series of novel deep blue light-emitting polymers (PF-4,6SOs) by combining fluorene-2,7-diyl and dibenzothiophene-S,S-dioxide-4,6-diyl (4,6SO). PF-4,6SOs demonstrated excellent solubility and high thermal stability. The introduction of the 4,6SO unit into the polyfluorene (PF) backbone caused distortion of polymer chains and affected conjugation. The peak emissions of PF-4,6SOs in the toluene solution and film were approximately 416 nm and did not exceed 437 nm, displaying deep blue emission and relatively high photoluminescence quantum yields (Φ_film) of over 50% in the film. The electron-withdrawing ability of the 4,6SO unit and its impact on the conjugation of polymers resulted in the weak intramolecular charge transfer (ICT) characteristics of PF-4,6SOs. With an increase in the content of the 4,6SO unit in the polymers from 5% to 20%, the lowest unoccupied molecular orbital (LUMO) energy level decreased from −2.17 eV to −2.37 eV. This reduction is beneficial for electron injection and transfer and can improve the properties of the device. The findings of this study indicated that introducing a 4,6SO unit into the polymer backbone was an effective approach for synthesising promising deep blue light-emitting polymers.