Electrochemically Based Light Emitting Devices from Sequentially Adsorbed Multilayers of a Polymeric Ruthenium (II) Comp
- PDF / 913,315 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 61 Downloads / 161 Views
Consequently, the charge density of the adsorbing
polymer and the previously adsorbed polymer are crucial in the multilayer adsorption process. Fundamentally, molecular parameters such as polymer pKa, the ionizable functional group type and the polymer molecular weight as well as polyelectrolyte solution parameters such as solution concentration, pH and ionic strength play an important role in determining the structural features of the resultant multilayers. Structural features such as the bilayer thickness and the composition of the polycation/polyanion building block and the interpenetration between the polycation/polyanion layers are key factors in determining the performance of devices. From this point of view, the layer-by-layer sequential adsorption processing technique provides a possibility to optimize device characteristics by simply controlling the thin film processing parameters as mentioned above. In this paper, we focus on light emitting devices made from sequentially adsorbed multilayers of a Ru(bpy)3 2 + polyester and poly(acrylic acid). As will be presented, by controlling the thin film processing conditions such as solution pH, we can systematically alter the bilayer thickness and the composition of the Ru(bpy)3 2 + polyester/PAA building block. This in turn has made it possible to dramatically alter and optimize the device performance. EXPERIMENT The chemical structure of the polymeric ruthenium (II) complex, Ru(bpy)3 2 + polyester 1, is shown in Scheme 1. A detailed description of the synthesis and properties of this material are described in another paper [4]. The structures of the polyelectrolytes, poly(allylamine hydrochloride) (PAH) 2 and poly(acrylic acid) (PAA) 3, used for sequential adsorption 63 Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
processing are also shown in Scheme 1. Both the PAH (MW=50 - 65K) and PAA (MW=50K, 25% aqueous solution) are commercially available.
o
+CH2-CH+ H2-NH 3+CI-
- CO(CH)CCO
2 poly(allylamine hydrochloride) PAI
N
N-Ru-NQ
C1_2
--
N
1 Ru(bpy)32+ polyester
CH2 _-CH-
3 poly(acrylic acid) PAA
Scheme 1 Chemical structures of the polyelectrolytes used for sequential adsorption processing. Solutions of the polycations and the polyanion were prepared by dissolving polymers in Millipore water to a concentration of lxl0-2 M. Solution pH was adjusted by adding hydrochloric acid HCI or sodium hydroxide NaOH. The rinsing water was prepared by adjusting the Millipore water to the same pH as that of the polyelectrolyte solutions. Prior to multilayer adsorption, the polyelectrolyte solutions were filtered through a 0.45 ntmfilter. Sequentially absorbed multi-bilayers of Ru(bpy)3+ 2 polyester and polyanion PAA were made by the automatic alternate dipping of the substrates in solutions. Each step for adsorption of the polycation or the polyanion in their solutions takes 10 minutes. Following the adsorption process, the substrate was rinsed by pH adjusted Millipore water three times. A single bilayer of PAH/PAA (pH=3.5 for both) was hand
Data Loading...
