Oligo(phenylenevinylene)s end-capped with phenothiazine or triphenylamine
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L4.44.1
Oligo(phenylenevinylene)s end-capped with phenothiazine or triphenylamine H. Detert, O. Sadovski Institut für Organische Chemie, Johannes Gutenberg-Universität Mainz Duesbergweg 10 – 14, 55099 Mainz, Germany
ABSTRACT Monodisperse oligo(phenylenevinylene)s end-capped with arylamines have been prepared via Horner Olefinations from bisphosphonates and arylaminobenzaldehydes. The influences of the conjugation length, different arylamine end groups, and of side chains with various electronic character on the electrical and optical properties of the chromophores are investigated. The elongation of the π-conjugated segment from 3 to 5 rings gives rise to bathochromic shifts of the electronic spectra and a slight increase of the oxidation potential. The same but more pronounced is true when the central electron donating ethers are replaced by the strong acceptor alkylsulfone. The electronic spectra of chromophores with triphenylamine and with N-alkylphenothiazines as end groups are quite similar, but the heterocyclic unit reduces the oxidation potential. The incorporation of a chromophor into a segmented copolymer has only negligible effect on the optical and electrical properties.
INTRODUCTION Aromatic oligoamines like TPD have a long tradition as hole transporting / electron blocking materials in light emitting diodes [1 – 3] and polymers based on (alkoxy-substituted) phenylenevinylene units are used widely as emissive layers in these devices [4 – 6]. Some chromophores combining hole transporting arylamines and strongly emissive arylenevinylene segments have been described, in one class, the amines are side chains on the conjugated polymer, [7, 8] a second group uses the motif of a chain of connected OPV-segments. [9 – 14] In contrast to OPVs linked via silylene or ether groups, [12, 15] the amines as connectors do not completely interrupt the conjugation along the main chain and they are able to localise and stabilise positive charges. [9, 10] It was demonstrated, that these polymers show outstanding photoconductivity and low threshold voltages when used as emissive layers in LEDs. [14] In particular amino-distyrylarenes have been investigated. [9 –17], a polymer containg phenothiazine has been described recently by Wu and Chen. [15] The synthesis, optical and electrical properties of triphenylamine- or N-alkylphenothiazine-terminated OPVs with 3 or 5 benzene rings in the conjugated system and side chains of different electronic character are reported here.
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L4.44.2
EXPERIMENTAL The synthesis of the title compounds was performed by Horner olefination of nitrogencontaining benzaldehydes 1 – 4 and substituted bisphosphonates 4, 5, 6 in figure 1. CHO
CHO H17C8
N 1 R
S
N
2
3
OHC
PO(OEt)2 n
(EtO)2OP
n
CHO
S
N
R
N S
4 n = 0, R = OC8H17 5 n = 1, R = OC
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