ELSEVIER Synthetic Metals 101 (1999) 96-97 Conformation studies on layers of soluble poly(pam-)phenyIenevinylenes R. ReseY, B. Tertinek”, S. Tasch”, A. Daveyb, W. Blaub, H. -H. HGrhold”, H. RostC, G. Leisinga a Institut fiir Festko”rperphysik, Teclrnische U&ersh& Grar, Petersgasse 16, A-8010 Graz, Austria b Polymer Research Centre, Physics Department, Tririity College Dublin, Dublirr 2, Ireland ’ Instit.ut fiir Organische urnd itiakrorrlolel-,ulare Chernie, Universitb? Jerza, Humboldtstrafie 10, D-07743 Jena, Germany Abstract Layers of two soluble poly(para-jphenylenevinylenes (PPV), one with octoxy (act-PPV) the oth& with 4-phenoxyphenyl sidechains (DPOP-PPV) are character&d by X-ray diffraction. The act-PP1’ layer shows wnicrystallinity while the DP-OP- PPV layer is in an anlorphous state. The crystallinity of act-PPV is about 20% The crystalline and the aulorpllous state of act-PPV show sinlilar features: i) the octoxy sidechains separate the PPV backbones to a distance 1.3...16a; ii) the PPV backbones pack close together, distances 3.8...4.5.& are observed. The antorphous state of DPOP-PPV is isotropic. No correlation between the PPV backbones could be observed. Steric hindrance, the stiffness of the phenoxy sidegroups pronlotes the anlorphous state of DPOP-PPV. Keywords: X-ray dijfraction, amorphous thin jibs, poly(pi~enylene oinylene) derivatives 1. Introduction Soluble polynlers based on the polyphenylenevinylene (PPV) backbone are promising candiatatas for industrial apphcation as rlectroactivr layers in light enlitting devices (LED) [I]. Good ii1111 processing could be achiewrl when the PPV-backbone is nlodifiecl by solubilizing side groups, i) either with flexible sidechains attached to the phenylene unit [2] or ii) with phenyl groups as substituent at the vinyl unit [3]. The packing of the polyiner chains and the orientation of the polynler chains relative to the substrate are inlportant paralueters for the perfornlance of LEDs. It has been shown that the packing of oligomers influence the luminescence properties [4] and that the electrical transport through elec- troactive layers depends strongly on the orientation of the oligonwrs relative to the substrate [5]. 2. Experimental The chentical structures of the investigated PPV based sol- uble polymers are depicted in Figure 1. The first polp- lner (act-PPV, ~fvI,(VPO)=11800g/~iiol, X,,,=421nnl [S]) is an ordered condensation copol~nler built by a sequence of two different repeat units, each containg two octoxy sidechains and all-trans double bonds. The side-groups of the second polynter (DPOP-PPV. h-I,(VPO)=2OOOOg/l~~ol, x mas=363111x1 [8]) are phenoxyphenyl groups. in contrast they are bonded at the vinylene units of the PPV-backbone to give a very voluminous and distorted structure. Layers of both polyiners are prepared on a silicon single crys- tal by casting front a toluenr solution, obtaining a thickness C8Hl76 I W-h70 act-PPV 0 0 DPOP-PPV Fig.1: Cheiuical fornwla of the copoly&ter act-PPV and of the polynler DPOP-PPV. of several /IYIL. X-ray diffraction expcrinlents were perfornwd in O/20 gtwnetry, the sawple was exposed to the prinlary bean1 of CuKn radiation at different tilt angles ,Q (Euler geonletry). The scattering contribution of the silicon siq$e crystal was substraced front the experinlental data. In case of DPOP-PPV the experinlental intensity was cor- rected for the scattering of -the substrate, polarisation and absorption The corrected intensity was transfornled to the reduced intensity function i(s), taking s as the value of the scattering vector s = F”si& [Y]. 3. Results and Discussion The experimental results for act,-PPV are depicted in Fig- ure 2. O/30 scaus in a region front B...W are shown, the 0379~6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: so379-6779(98)0 1234-x