Luminescence properties of soluble 2,2′,7, 7′-tetrakis(2-(9- hexyl-9H-carbazol-3-yl)-vinyl)-9, 9′-spirobifluorene-labeled dendrimers: Photoluminescence and electroluminescence

New light emitting dendrimers were synthesized by reacting 3,5-bis-(3,5-bis-benzyloxy-benzyloxy)-benzoic acid or 3,5-bis-[3,5-bis-(3,5-bis- benzyloxy-benzyloxy)-benzyloxy]-benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue-emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10, revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3, 9, and 10 showed luminances of 1021 cd m^-2 at 5 V, 916 cd m^-2 at 6 V, and 851 cd m^-2 at 6.5 V, respectively. The largest dendrimer, 10, bearing a greater number of benzyloxy dendrons, exhibited a blue-like emission with CIE 1931 chromaticity coordinates of x = 0.16 and y = 0.13, which is due to the influence of a higher shielding effect.