Poly(spirobifluorene)s Containing Nonconjugated Diphenylsulfone Moiety: Toward Blue Emission Through a Weak Charge Transfer Effect

Instead of conjugated dibenzothiophene-S,S-dioxide (DBTSO), we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-deficient unit into the main chain of poly(spirobifluorene)s (PSFs). Because of the weaker electron affinity of DPSO relative to DBTSO, the charge transfer from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be effectively prevented. Consequently, the resultant polymers containing DPSO moiety show pure blue emissions, which is different from DBTSO-based PSFs that exhibit undesired green emissions. With a single-layer device configuration, a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130 cd/m2 have been realized for the polymer PSFDPSO03. The corresponding CIE coordinates are (0.17, 0.18), nearly independent of the applied current density from 2 to 592 mA/cm2. These results indicate that tuning the electron affinity of the incorporated electron-deficient units is a very promising strategy to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability.