Synthesis and luminescence properties of orange-red light-emitting polymers

Abstract

A series of 2,5-dialkoxy substituted poly(1,4-phenylenevinylene) derivatives containing a rigid and bulky cyclohexyl group on the arylene ring, poly[2-(7-cyclohexylheptyloxy)-5-butoxy-1,4-phenylenevinylene] ($PBC_yH_pPV$), Poly[2-(6-cyclohexyl methoxy hexyloxy)-5-butoxy-1,4-phenylenevinylene] ($PBC_yH_xPV$), Poly[2,5-bis-(6-cyclohexylmethoxy-hexyloxy)-1,4-phenylenevinylene] ($PDC_yH_x PV$) were synthesized through Gilch polymerization route. The synthesized polymers showed good solubility in common organic solvents and good thermal stability up to 370℃. The maximum absorption peaks of the thin films made from $PBC_yH_pPV$, $PBC_yH_xPV$ and $PDC_yH_xPV$ were at 513 nm, 515 nm and 511 nm, respectively. Photoluminesence (PL) maximum emission peaks of above polymers appeared at 590 nm, 597 nm, 590 nm, respectively. The electroluminescence (EL) properties were studied through EL spectra, current-luminance-voltage characteristics. The EL maximum peaks of the synthesized polymers appeared at 585 nm, 590 nm, and 590 nm, respectively. But these polymers common to all showed another shoulder peak around 630 nm strongly. $PDC_yH_xPV$ showed the highest EL efficiency and EL power than the others due to the dilution effect by two rigid and bulky cyclohexyl groups. Novel poly(p-phenylenevinylene) derivatives with an electron-withdrawing cyanophenyl group on the polymer backbone, poly[2-(2’-ethylhexyloxy)-5-(4’-cyanophenyl)-1,4-phenylenevinylene] (PEHCNPV) and poly[2-dimethyloctyl-silyl-5-(4’-cyanophenyl)-1,4-phenylenevinylene] (PSi8CNPV), were synthesized via the Gilch polymerization. These polymers were completely soluble in common organic solvents and showed good thermal stability up to 400℃. Surprisingly, they showed very high glass transition temperatures (above 180℃), indicating that electroluminescenece (EL) devices constructed from these polymers should have good thermal stability. The presence of the electron-withdrawing cyanophenyl group lowered the HOMO and LUMO...