Hyperbranched poly(fluorenevinylene)s obtained from self-polymerization of 2,4,7-tris(bromomethyl)-9,9-dihexylfluorene

Hyperbranched poly(fluorenevinylene)s (HF0.04-HF0.17 and HF0.08-cap) were prepared from 2,4,7-tris(bromomethyl)-9,9-dihexylfluorene (A) by the Gilch reaction (the numbers represent monomer concentration in mmol/mL; cap: end-capped by benzyl bromide). The structural analysis of the hyperbranched products was obtained from their ¹H NMR spectra, from which an almost linear relationship between degree of branching (DB) and monomer concentration has been correlated. The absorption peaks blue-shifts significantly from 430 nm for linear LF0.17-cap counterpart, which was prepared from 2,7-bis(bromomethyl)- 9,9-dihexylfluorene (A′), to 372 nm for the hyperbranched poly(fluorenevinylene)s which degenerates further at higher degree of branching. However, the photoluminescence spectra of the HF films show peaks at ca. 467-468 nm, which is close to that of the LF0.17-cap film (473 nm), suggesting effective photoexcited energy transfer occurs between segments in the HF samples. The maximal luminance (2180 cd/m²) and maximal luminance efficiency (0.89 cd/A) of the electroluminescent device using end-capped hyperbranched poly(fluorenevinylene) as emitting layer (ITO/PEDOT/HF0.08-cap/Ca/ Al) are superior to those from the LF0.17-cap (1452 cd/m², 0.47 cd/A) and other hyperbranched polymers without end-capping (184-26 cd/m², 0.01-0.09 cd/A). Current results indicate that both hyperbranched structure and end-capping contribute to enhanced optoelectronic performance in the poly(fluorenevinylene)s.