LIGHT-EMITTING ELECTROCHEMICAL DEVICES FROM SEQUENTIALLY ADSORBED MULTILAYERS OF A POLYMERIC RUTHENIUM(II) COMPLEX AND VARIOUS POLYANIONS

We have fabricated light emitting devices based on sequentially adsorb ed multilayers of an electrochemiluminescent active ruthenium (II) com plex, Ru(bpy)(3)(2+) polyester, and various polyanions including a sma ll molecule Ru(II) dye, sulfonated poly(p-phenylene), sulfonated polys tyrene, poly(methacrylic acid) and poly(acrylic acid). Thicknesses per bilayer (polycation plus polyanion) ranging from 7 to 59 Angstrom wer e obtained by changing the nature of the polyanion. Our results reveal ed that the nature of the polyanion does not influence the optical tra nsitions of the Ru(II) complex. Device performance, however, was drama tically dependent on the type of polyanion used. Symmetric behavior wa s exhibited from devices fabricated with polyanions containing weakly acidic carboxylic acid groups whereas more diode-like behavior was obs erved from the devices fabricated with polyanions containing the stron gly acidic sulfonic acid group. Our best devices to date utilize poly( acrylic acid) as the polyanion and exhibit an external quantum efficie ncy of 3.2% (photons/electron) and a maximum light output of about 135 0 nW (40 cd/m(2)). (C) 1998 Elsevier Science S.A. All rights reserved.