Synthesis and Electronic Spectra of Substitutedp-Distyrylbenzenes for the Use in Light-Emitting Diodes

Abstract

Poly(p-phenylenevinylene) and its derivatives are one of the preferred groups of materials for the use as emissive layer in organic polymer light emitting diodes [1 -4]. Several groups investigated the photochemistry and particularly the photophysical behaviour of these polymers in order to establish knowledge of the fundamental properties that are responsible for the efficiencies of the devices as well as their amelioration [3 -9]. However, the fact that the parent polymer is insoluble and intractable prevents its complete characterization so that systematic investigations on structure-property relationships are almost impossible. A part of this problem can be circumvented by the investigation of model compounds. This approach, the estimation of the properties of a polymer by investigation of oligomers as model compounds is widely used, especially in the field of conjugated polymers [10 -15].Oligo(phenylenevinylene)s are useful as model compounds for the corresponding polymers and as luminescent material in Organic Light Emitting Diodes (OLEDs). Herein, the synthesis and the electronic spectra of a series of substituted distyrylbenzenes (DSBs) with a great variety of position, number, and character of substituents is reported. In order to elucidate the influence of different substitution patterns on the absorption and emission spectra, electron donors like dimethylamino and alkoxy side chains, a well as electron withdrawing groups like sulfones or nitriles and combinations of them were studied. Electron-donating ether groups have been used extensively in the field of conjugated polymers, as they reduce the band gap and allow to attach solubilising side chains. Sulfones and nitriles on the other hand, are electron withdrawing, which is especially important for a balanced charge carrier injection into the emitting material in a LED [16,17] Abstract. The influence of substitution on the absorption and Luminescence spectra of oligo(phenylenevinylene)s has been studied using distyrylbenzene (DSB) as a model compound. The degree, character, and pattern of substitution was varied systematically, altering the electronic properties of the DSB, the wavelength of the emitted light could be tuned over a for the application of metals with higher work function as cathode [18]. To allow comparison of the influences of different substitution, the basic chromophore, DSB, remains unchanged. SynthesisSeveral reactions are suitable to synthesize 1,4-distyrylbenzenes with two identical styrene units. Besides aldol-type condensations like Knoevenagel and Siegrist, Heck and Wittig-Horner reactions are most versatile. For the latter one, the starting materials are terephthaldialdehydes or 1,4-bis(halomethyl)benzenes for the central ring and benzylic halides or benzaldehydes for the lateral units.The majority of the distyrylbenzenes investigated here (6a -h) was synthesized starting with the MichaelisArbusov reaction of easily accessible 1,4-bis(chloromethyl) benzenes [19] to bisphosphonates 1a, 1b followed by PO-activated olefination ...

Novel Synthesis of Protected Thiol End-Capped Stilbenes and Oligo(phenylenevinylene)s (OPVs)

“…Other methods that are used successfully in this work include McMurry 24 and Knoevenagel , reaction procedures. Again, thioesters would have been absolutely intolerable, whereas these methods proved fully compatible with t -Bu sulfide protection.…”

Linear and Angular Distyrylpyrazines with Terminal Donor Groups: Synthesis, Solvatochromism, and Acidochromism of the Electronic Spectra

“…π -Conjugated oligomers [1] like oligo(phenylenevinylene)s [2, 3] and their heterocyclic derivatives [4–7] have attracted much interest for the application as active materials in organic light-emitting devices. The substitution of conjugated polymers [8] and oligomers with side chains of different types has been widely used to improve solubility and mechanical behaviour of these materials.…”