Red emitting phenothiazine dendrimers encapsulated 2-{2-[2-(4-dimethylaminophenyl)vinyl]-6-methylpyran-4-ylidene}malononitr ile derivatives

Abstract

New red light emitting dendrimers were synthesized by reacting 2-[2-(2-{4-[bis(6-hydroxyhexyl)amino]phenyl}vinyl)-6-methylpyran-4-ylidene]malononitrile (15) or 2-[2,6-bis(2-{4-[bis(6-hydroxyhexyl)amino]phenyl}vinyl)pyran-4-ylidene]malononitrile (16) with 3,5-bis{3,5-bis[2-(10-hexyl-10H-phenothiazin-3-yl)vinyl]benzyloxy}benzoic acid (9) by DCC catalyzed esterification. Two kinds of red emitting core dyes capable of electronic excitation via Forster energy transfer were encapsulated by phenothiazine (PTZ) dendrons. Photoluminescence (PL) studies of the dendrimers demonstrated that, at the high density of a PTZ dendron, a significantly high-energy transfer to the core is achieved as a result of the large overlap between the absorption spectrum of a core emitting dye and the PL spectrum of the PTZ dendron. The electroluminescence (EL) spectra of multilayered devices showed red emissions, similar to those observed in the PL spectra of dendrimer thin films. The multilayered devices showed a luminance of 490 cd/m(2) at 254 mA/cm(2) (11.4 V) for 17 and 210 cd/m(2) at 321 mA/cm(2) (11.7 V) for 18. The EL quantum efficiency of 18 (eta(ext) = 0.56%) increased with an increase in the density of a light-harvesting PTZ dendron. The larger dendrimer, 18 bearing a more polar emitting core exhibited a considerably pure red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.64, y = 0.34.