The Synthesis, Condensation, and Luminescence of Stilbenoid Oligomers with Alkoxysilane End Groups
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The Synthesis, Condensation, and Luminescence of Stilbenoid Oligomers with Alkoxysilane End Groups
H. Detert, E. Sugiono Institute of Organic Chemistry, Johannes Gutenberg-University Mainz, Duesbergweg 10 – 14, 55099 Mainz, Germany
ABSTRACT
A synthetic route to highly luminescent organic semiconductors with curable alkoxysilyl groups is described. Monodisperse oligo(phenylenevinylene)s are rigidly connected to di- and triethoxysilanes via Heck reactions or via cross-metathesis. Hydrolysis of the silicic esters yields silanols condensing to linear and cyclic oligo-OPV-siloxanes or to three-dimensional networks, thus allowing the transformation of small molecules to fluorescent materials with well-defined chromophores. Transparent films are obtained by casting of soluble cyclosiloxanes and from OPV-silanetriols, the latter can be cured to insoluble networks.
INTRODUCTION
Poly(phenylenevinylene) and its derivatives are among the most intensively investigated class of organic semiconductors [1]. Oligomers serve as model compounds for the polymers but are also electronic materials in their own right [2]. An important prerequisite for potential applications of stilbenoid oligomers in light emitting diodes is their strong fluorescence. Monodisperse OPVs can be prepared in high purity and free of structural defects, a tuning of the luminescence and the electronic properties is possible upon substitution with electron withdrawing or donating groups [3]. The application of these materials is often limited by their strong tendency towards crystallization. Frequently, amorphous films can be obtained by using polymeric matrices or incorporation of the chromophores into a flexible polymer chain or as side chains [4, 5]. The hydrolysis of di- and trialkoxysilanes yields silanols condensing to linear and cyclic oligosiloxanes or to polymeric networks. The connection of stilbenoid chromophores with alkoxysilyl groups yields soluble monomers, which can be converted to film-forming siloxanes or organic-inorganic hybrid materials with highly fluorescent and well-defined conjugated units.
EXPERIMENTAL
Details of the experimental procedure for the synthesis of the alkoxy-substituted oligo(phenylenevinylene)s with terminal bromine and iodine atoms (1 - 6), their Pd-catalyzed vinylation (7 - 9) and subsequent cross-metathesis with vinyl silane 10 to yield the triethoxysilylsubstituted chromophores 12 - 14 (scheme 1) have been reported earlier [6]. Styrene 15 [7] was
C5.32.1
used for the elongation of the conjugated systems via Heck reaction to yield the OPVs 16 – 18 with diethoxymethylsilyl moieties (scheme 1). OC8H17
X = I, n = 2 - 4 Pd(OAc)2, P(oTol)3 NEt3, DMF, (100 °C, 8 h)
X H17C8O
OC8H17
Ethene (30 bar)
n
1-6 X = Br, n = 1 - 3 Pd(OAc)2, P(oTol)3 NEt3, DMF (100 °C, 3 h)
OEt Si OEt
15
7: n = 1 8: n = 2 9: n = 3
H17C8O
n
[Ru(PCy3)2CHPh]Cl2 benzene, 20 °C
Si (OEt)3 10
OC8H17
OC8H17 OEt Si n OEt
H17C8O
H17C8O
n
16: n = 1 17: n = 2 18: n = 3
OEt Si OEt OEt
12: n = 1 13: n = 2 14: n = 3
Scheme 1. Functionaliz
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