Light-Emitting Organic Materials with Variable Charge Injection and Transport Properties

Abstract

Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron-or hole-conducting core were designed for tunable charge injection and transport properties. Representative glassy-isotropic and glassy-liquid-crystalline (i.e., noncrystalline solid) materials were synthesized and characterized; they were found to exhibit a glass transition temperature and a clearing point close to 140 and 250°C, respectively; an orientational order parameter of 0.75; a photoluminescence quantum yield up to 51%; and HOMO and LUMO energy levels intermediate between those of blue-emitting oligofluorenes and the ITO and Mg/Ag electrodes commonly used in organic light-emitting diodes, OLEDs. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.

Star Mesogens (Hekates)—Tailor‐Made Molecules for Programming Supramolecular Functionality

“…The resulting nematic LC glasses are interesting for large area nonabsorbing polarisers, optical notch filters and reflectors and for polarized fluorescent films. [65] Highly fluorescent materials were obtained from triazine and benzene derivatives [66,23,39] and benzene-1,3,5-triscarboxamides. [67] The latter forms a fluorescent gel, in which only the hydrogen-bonded assemblies of the star-molecules prevent the fast nonradiative relaxation.…”

Fluorene-Based Conjugated Oligomers for Organic Photonics and Electronics

“…Some also introduce these charge-transporting moieties as a central core with arms attached in direct conjugation [91,102] or as a central unit in the oligomer [103]. Direct conjugation with these moieties does influence their electronic and optical properties, which can be avoided by employing spiro-linked transport moieties [104], 9-position attachment of these arylamines [105], or alkyl spacers between the moieties [106,107].…”

“…Attachment of oligofluorenes through a flexible alkyl spacer on the 2 -position of the oligomer to a charge transport core allows the pendant oligomers to align into nematic films through deformation of the spacer [106]. Synthetically, this is accomplished by Suzuki coupling of the boronic acid of the oligofluorene to allyl bromide, followed by activation of the allyl group with hydroboration for Suzuki coupling to a halogen-bearing functional core.…”

“…Lastly, an interesting case is that of hybrid oligofluorene compounds [106,139], one of which is shown as the last example in Fig. 7 (compound 49).…”

“…In addition, through end-capping [93][94][95][96][97][98][99][100], substitution at the C-9 position [105], direct connection to such a core [91,102], or non-conjugated attachment through a flexible spacer [106,176], functionalization with electron-rich moieties contributes additional oxidation peaks in the CV scans. Similar non-conjugated attachment of electron-deficient moieties results in additional peaks in the reduction scans [106,176].…”