Synthesis and Incorporation of Thienylene Vinylene Oligomers in Main-Chain Copolymers
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L.G. MADRIGAL, E. H.ELANDALOUSSI, C. W.SPANGLER Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, uchcs@ earth.oscs.montana.edu
ABSTRACT Poly [2,5-thienylene vinylene] (PTV) has been studied extensively over the past decade for both its metallic conductivity behavior upon chemical doping, as well as its interesting third order nonlinear optical properties. PTV oligomers have been synthesized by our group 1 , as well as others 2 , and the formation of polaron-like radical-cations or bipolaron-like dications by oxidative doping has been demonstrated. In this paper we describe a general synthetic approach to PTV oligomers functionalized for copolymer formation by step-growth reaction. INTRODUCTION We have recently reviewed the synthesis of thienylene polyenylene oligomers and polymers, with particular emphasis on charge-state incorporation in these materials 3 . When examining the oxidative doping of these oligomers in solution (SbCI5 / CH 2 CI 2 ), it is clear that both the neutral it - l* transition and the shift in oscillator strength upon doping is more well-defined than that observed in the fully conjugated polymer. Doping studies of the oligomers in solution, however, are complicated by the insolubility of oligomers longer than the pentaenel. Over the past few years, it has been shown that incorporation of alkyl groups (e.g. butyl) in the 3 and 4 positions of each thiophene ring greatly enhances the solubility of these compounds to the point that they can now be derivatized in the terminal axpositions with the expectation that they can be incorporated as formal repeat units in well-described copolymers. For example, we have described the incorporation of dithienyl polyene repeat units with up to ten ene units in various copolymer formulations utilizing this approach 4 , exemplified by the dithienylhexatriene incorporated polyurethane shown below: Bu Bu
BBu
S
CR2OCONH(CH 2)6NHCO
SYNTHESIS OF PTV-OLIGOMERS CONTAINING SOLUBILIZING GROUPS During the past two years we have synthesized PTV oligomers solubilized with butyl substituents from dimer through pentamer. The synthetic approach is outlined in Schemes 1 and 2. Roncali and coworkers have recently described an almost identical approach to these materials 5 . The alkyl group substitution pattern renders these materials soluble in most organic solvents. The a positions on the terminal rings of these oligomers remain reactive under Vilsmeier conditions, yielding reactive CHO groups. Reduction to terminal CH 2 OH groups thus provides functionalities that can be polymerized in a variety of step-growth condensations.
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Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
Bu
Bu B
B
,
,Br CMR 2 PBu3
OC-.-CHO +
OHO KOt-i~u
/
BuS.
Bu-- S
Bu
13DM F
SPO C
Bu"
•DF
/1
,2-DCE
Bu
CHO,/• I S. Bu
B
B
KOt-Bu
1
•+
CH 2PBu 3 ,Br
THF
Bu
Scheme 1. Synthesis of PTV-dimer and tetramer
648
Bu
BS
BuB
ICHO s
CHO
B
S
Buu
Bu
Bu.
KOt-Bu
I
"
CH2ABu,JBr THF
Bu au
i. TiC04 / Zn; ii. POC13
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