Highly enhanced and stabilized blue-luminescent polyfluorene

Abstract

A new POSS (Polyhedral Oligomeric Silsesquioxane) substituted polyfluorene was syn-thesized from nickel-catalyzed Yamamoto coupling reaction. The synthesized polymers could be well characterized by $^1H-NMR$, FT-IR and elemental analysis. PFPOSSs (POSS substituted polyfluorenes) showed almost the same UV-vis absorption and PL spectra as poly(dialkylfluorene)s, both in a p-xylene solution and on a quartz film (1 wt% p-xylene spin coated, 2000 rpm, 60s). PL spectra of poly(dialkylfluorene)s showed greater aggregation/excimer emission because of the interchain aggregation tendency of poly(dialkylfluorene)s in solid states. However PL spectra of PFPOSSs on the quartz film showed reduced aggregation/excimer formation because the bulky POSS group prohibited interchain interactions. This effective isolation effect and the high thermal stability of the POSS unit also improved the thermal stability of PFPOSSs even after thermal annealing at 150℃. Of great interest is the fact that the fluorescence quantum yields $(Φ_{FL})$ of PFPOSSs were enhanced up to 100 % as the POSS ratio increased. Light-emitting diode (LED) device fabricated with ITO/PEDOT-PSS/Polymer/Ca/Al con-figuration showed very stable blue light emission with a maximum EL peak at 423 nm and highly reduced aggregation/excimer green emission.